ZNOTES.ORG UPDATED TO 2023-2025 SYLLABUS CAIE IGCSE PHYSICS SUMMARIZED NOTES ON THE THEORY SYLLABUS Prepared for Maryam for personal use only. CAIE IGCSE PHYSICS 1. Motion, Forces and Energy 1.1. Physical Quantities and Measurement Techniques The area of a square with sides 1 cm long is 1 square centimetre (1 cm²). Area formula: area = length × breadth. SI unit of area: square metre (m²), which is the area of a square with sides 1 m long. Volume Units and basic quantities A standard or unit must be chosen before a measurement can be made. The size of the quantity to be measured is found using an instrument with a scale marked in the unit Three basic quantities are measured in physics: length, mass, and time. Units for other quantities are based on length, mass, and time. The SI (Système International d’Unités) system is a set of units used in many countries Length Unit of length: metre (m) 1 decimetre (dm) = 10⁻¹ m 1 centimetre (cm) = 10⁻² m 1 millimetre (mm) = 10⁻³ m 1 micrometre (μm) = 10⁻⁶ m 1 nanometre (nm) = 10⁻⁹ m Multiples for large distances: 1 kilometre (km) = 10³ m 1 gigametre (Gm) = 10⁹ m Many length measurements are made with rulers/meter rule For any length less than a meter, we use a tape measure Volume is the amount of space occupied. Unit of volume: cubic metre (m³). Commonly used unit for volume: cubic centimetre (cm³). Volume of a cylinder: V = πr2 h A measuring cylinder can measure the volume of a liquid. Ensure the cylinder is upright and the eye is at bottom level of the meniscus. Time Unit of time: second (s). Time-measuring devices use oscillations. Choose a timer that is precise enough for the task (e.g., a stopwatch for the pendulum period or a millisecond timer for measuring the speed of sound). Scalars and Vectors Note: Take ± readings for accuracy Area WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Scalar quantity: has magnitude (size) only. Examples: distance, speed, time, mass, pressure, energy, temperature. Vector quantity: described by both magnitude and direction. Examples: force, gravitational field strength, electric field strength, weight, velocity, acceleration, momentum. Representing Vectors: a straight line with length indicating the magnitude and an arrow showing direction. Adding scalars: ordinary arithmetic. Adding vectors: geometrically, considering both magnitude and direction. For two vectors, FX and FY, at right angles: The magnitude of the resultant F = FX2 + FY2 Distance and displacement Distance is a length a body travels between two points. It is a scalar quantity. Displacement is similar to distance but as it is a vector quantity, direction is also considered. Distance-Time Graph Examples Angle θ between FX and F tan θ = FFXY At rest ( BC). Constant speed (AB and CD) Speed is higher when the gradient is steeper. For example, the speed of the train at CD is 2m/s, but that at AB is 1m/s. It is higher in CD, which can be seen as CD being steeper. Non-Constant Speed When speed changes, the gradient of the distance-time graph varies. Upward curve of increasing gradient: accelerating. The upward curve of decreasing gradient: decelerating. Example: 1.2. Motion WWW.ZNOTES.ORG Gradient of the tangent at T: Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS AB 40m BC = 2s = 20m/s Velocity is the distance travelled in unit time in a given direction. Ie. Velocity = Speed given in a specific direction. Speed is the distance travelled in unit time. Example: If two trains travel due north at 20 m/s, they have the same speed and velocity due north. If one travels north and the other south, their speeds are the same, but not their velocities. Key definition: Velocity is the change in displacement per unit of time. Velocity formula: in a given direction Velocity = Distance moved = Time taken Displacement T ime Speed Speed is the distance travelled by a body in unit time. When the distance travelled is (s) over a short time period (t), the speed (v) is given by: v = st Key definition: Speed is the distance travelled per unit time. General formula: distance travelled Average speed = Total Total time taken Example: If a car travels 300 km in five hours, its average speed is: Average speed = 3005 hkm = 60 km/h Velocity is the speed in a given direction. A body's velocity is uniform or constant if it moves at a steady speed in a straight line. Velocity is not uniform if the body moves in a curved path. Speed and velocity units are the same: km/h, m/s. Note: Speed is a scalar quantity and velocity a vector quantity. Displacement is a vector, unlike distance which is a scalar Acceleration When the velocity of an object changes, the object accelerates. Acceleration is defined as the change of velocity in unit time: Velocity WWW.ZNOTES.ORG Acceleration = Δv Δt Time (s) 0 1 2 3 4 5 6 Speed (m/s) 0 5 10 15 20 25 30 Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Example: If a car starts from rest and reaches a velocity of 2 m/s after 1 second, its acceleration is 2m/s2 , due north Key definition: Acceleration is the change in velocity per unit time. Example: For a steady increase of velocity from 20 m/s to 50 m/s in 5 seconds: Acceleration = (50−20),m/s = 5s 2 6m/s Acceleration is a vector, and its magnitude and direction should be stated. For motion in a straight line, the magnitude of the velocity equals the speed, and the magnitude of the acceleration equals the speed change in unit time. Example: A car accelerating on a straight road with the following speeds: The speed increases by 5 m/s every second, and the acceleration is constant at 5 m/s². Acceleration is positive if the velocity increases. Acceleration is negative if the velocity decreases (also called deceleration or retardation). The linear shape (AB) of the graph indicates constant acceleration. The speed increases by 4 m/s every second, indicating constant acceleration. Variable Acceleration Example 1: The figure shows acceleration from rest, constant speed, and deceleration. Speed-Time Graphs Speed-time graphs plot the speed of an object against time. Used to solve motion problems. Constant Speed Example: AB is a speed-time graph for an object moving with a constant speed of 25 m/s. A straight horizontal line on a speed-time graph indicates constant speed. Example 2: The figure shows changing acceleration with a curved shape. Constant Acceleration WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS First Equation If an object is moving with constant acceleration ( a ) in a straight line and its speed increases from ( u ) to ( v ) in time ( t ): Acceleration is given by: a = v−u t Rearranging gives: v = u + at Second Equation For an object moving with constant acceleration, its average speed equals half the sum of its initial and final speeds: Speed increases over time, but by a smaller amount each second, indicating decreasing acceleration. Using Gradient to Calculate Acceleration The gradient of a speed-time graph represents the acceleration. For constant speed, the gradient is zero, indicating zero acceleration. For constant acceleration, the gradient is given by: \n Y <i>2−Y </i>1 Δy Gradient = Δx = X<i>2−X</i>1 For changing acceleration, the gradient changes, indicating changing acceleration. An object accelerates if the speed increases and decelerates if the speed decreases with time. (Equation 1) Average speed = u+v 2 If (s) is the distance moved in time (t), then: Average speed = st Combining these, we get s u+v t = 2 Rearranging gives: s = (u+v) ⋅ t (Equation 2) 2 Air Resistance and Free Fall Area Under a Speed-Time Graph In the air, a coin falls faster than a small piece of paper due to air resistance. In a vacuum, both fall at the same rate. Air resistance has a greater effect on light bodies compared to heavy bodies. Air resistance is negligible for dense, heavy objects at low speeds. Acceleration of Free Fall Measures the distance travelled. The rule applies even if acceleration is not constant. The distance equals the shaded area under the graph. Equations for constant acceleration All bodies falling freely under gravity accelerate uniformly if air resistance is negligible. This uniform acceleration is called the acceleration of free fall, denoted by ( g ). The value of (g) varies slightly but is about 9.8 m/s² on average. The velocity of a free-falling body increases by about 9.8m/s every second. A ball shot upwards with a velocity of 30 m/s decelerates by about 9.8 m/s every second, reaching its highest point after 3 seconds. As an object falls, air resistance increases, reducing its acceleration. WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Mass The mass of an object is the measure of the amount of matter in it. It is a measure of the quantity of matter in an object at rest relative to an observer. The standard unit of mass is the kilogram (kg), with the gram (g) being one-thousandth of a kilogram: 1g = 10−3 kg = 0.001kg Mass is different from weight, which is a gravitational force on an object with mass. Weight When air resistance equals the object's weight, it falls at a terminal velocity. Terminal velocity depends on the object's size, shape, and weight. A small, dense object has a high terminal velocity and accelerates for a longer distance. A light object or one with a large surface area, like a raindrop or parachute, has a low terminal velocity and accelerates over a shorter distance. Following is the velocity-time graph for a falling parachutist: Explanation: Initial Phase: When the parachutist jumps out of the plane, they experience free fall. During this phase, their velocity increases steadily due to the acceleration of gravity (approximately 9.8m/s2 acting downwards. The graph slopes upwards steeply. Slowing down of Parachute: Air resistance increases significantly when the parachutist deploys their parachute. This causes a decrease in acceleration, leading to a less steep slope on the graph. The parachutist’s velocity continues to increase but at a slower rate compared to free fall. Terminal Velocity: As the parachutist continues to fall, their velocity eventually reaches a maximum constant value known as terminal velocity. At terminal velocity, the forces of gravity and air resistance (drag) balance out, resulting in zero net acceleration. On the velocity-time graph, this appears as a horizontal line where the velocity remains constant. 1.3. Mass and Weight Weight is the gravitational force acting on an object that has mass. The weight of an object can vary with location due to differences in gravitational field strength. The unit of force is the Newton (N). Weight is measured in newtons and can be determined using a spring balance. Aspect Definition Units Measurement Dependency Mass Weight Measure of the amount of matter in Gravitational force acting on an object an object with mass Kilogram (kg), gram (g) Newton (N) This can be measured using a Measured using a spring balance or balance scale Independent of location and Depends on location and gravitational gravitational field field strength Symbol in Equations m (W ), or, (Fg ) Gravitational Field Gravity acts through space, causing objects not in contact with the Earth to fall towards it. Gravitational field strength (g) is the force per unit mass and is a vector quantity with magnitude and direction. On Earth's surface, g = 9.8 N/kg or 9.8 m/s^2, representing both the acceleration due to gravity and the gravitational field strength. 1.4. Density Definition Density (ρ) is the measure of mass per unit volume ρ= m V Standard units for density include kilograms per cubic meter (kg/m³) or grams per cubic centimeter (g/cm³). Calculation Methods WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Regular Shape: Measure mass (m) using a balance, and measure volume (V ) by direct measurement of dimensions. Irregular Shape: Measure mass (m) using a balance. Measure volume (V ) using displacement methods: Method 1: Immerse the object in a measuring cylinder filled with water, record the initial and final water levels to find volume. Liquid: To determine the mass of an empty container, add liquid, measure total mass, and subtract to find the mass of the liquid. Divide by the known volume to find density. Air: Measure the mass of a flask filled with air, then remove the air with a vacuum pump. Calculate air density by dividing the mass difference by volume measured using water displacement. Example Calculations Example 1: Calculate the density of copper given a mass 63 g of 63 g and a volume of 7 cm³ ρ = m V = 7 cm³ = 9 g/cm³ Example 2: Determine the mass of an aluminium sheet with a volume of 73 cm³ and a density of 2.7 g/cm³ m = ρ × V = 2.7 g/cm³ × 73 cm³ = 197.1 g Floating and Sinking: Method 2: Displacement Can. Fill the can until the spout. Immerse the object in the water and find the volume of water displaced. That volume of water is the volume of the object. Objects float or sink in liquids based on their density relative to the liquid's density. A higher-density object sinks in a lower-density liquid and vice versa. 1.5. Forces Force A force is a push or a pull that can change the motion, speed, or shape of an object. It can cause objects at rest to move or alter the direction of moving objects. Extension in Springs Springs follow Hooke's Law, where extension is proportional to the stretching force up to the limit of proportionality. Symbolically, extension ∝ stretching force Spring Constant The spring constant (k) measures the force needed to cause a unit extension in a spring. k = Fx , where (F ) is the force applied and (x) is the resulting extension. Load-Extension Graphs Used to graphically represent the relationship between applied force (load) and resulting extension in materials like springs. Non-linear graphs beyond the limit of proportionality indicate permanent deformation. WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Friction and Air Resistance Forces and Resultants Forces have magnitude and direction, represented by arrows in diagrams. Multiple forces acting on an object can be balanced (e.g. weight and support force) or have a resultant force. The resultant force is the single force that has the same effect as all forces acting together. A resultant force can change the velocity of an object by altering its speed or direction of motion. Forces like friction and air resistance cause objects to slow down and eventually come to rest. In their absence, objects would continue moving indefinitely with constant speed. Newton’s Second Law States that the acceleration of an object is directly proportional to the force acting on it and inversely proportional to its mass. Mathematically expressed as: F = ma where (F ) is the resultant force in newtons (N ), (m) is the mass in kilograms (kg ), and (a) is the acceleration in meters per second squared (m/s2 ). Proportional Relationships Acceleration (a) is directly proportional to the force (F ) when mass (m) is constant a∝F Acceleration (a) is inversely proportional to mass (m) when force (F ) is constant a ∝ m1 Newton’s First Law An object remains at rest or continues to move at a constant speed in a straight line unless acted upon by a resultant force. This means that no force is required to maintain constant velocity if no external forces act on the object. Units and Constant (k ) The unit of force, the newton (N ), is defined as the force that gives a 1 kg mass an acceleration of 1m/s2 k in F = kma equals 1 when m = 1kg and a = 1 m/s2 Resultant Force and Motion Resultant force (F ) causes an object to accelerate in the direction of the force. When forces are balanced, there is no acceleration, but changes in shape may occur due to internal forces within the object. Friction WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Friction is the force that opposes the motion o of one surface over another. It is essential for walking and gripping surfaces but can prevent proper movement on surfaces like ice. Types of Friction Static Friction: The frictional force that opposes the starting of motion between surfaces in contact. Kinetic Friction: The frictional force that opposes the motion of surfaces sliding past each other. Fluid Friction (Drag): Resistance encountered by an object moving through a fluid (air or liquid), increasing with speed and reducing acceleration. Effect of Force and Mass on Friction Increasing the force pressing surfaces together increases friction initially. Friction converts kinetic energy into thermal energy, causing a rise in temperature when contacting surfaces. Centripetal Force In a circular motion, an object moves in a curved path due to a force directed towards the centre of the circle. Despite constant speed, circular motion involves acceleration because velocity direction changes continuously. Acceleration towards the centre of the circle is necessary to maintain circular motion. Factors Affecting Centripetal Force Centripetal force magnitude depends on the following: Speed (v): Increasing speed increases centripetal force. Radius (r): Decreasing radius increases centripetal force. Mass (m): Increasing mass increases centripetal force. Role of Centripetal Force It ensures the object maintains a constant distance from the centre of the circle. Moment of a Force The turning effect of a force around a pivot point is called the moment of the force. It depends on both the magnitude of the force and the perpendicular distance from the pivot to the line of action of the force. Mathematically, the moment is given by: M =F ×d where d is the perpendicular distance from the pivot to the line of action of the force. The unit of moment is the Newton metre (N m). Balancing a Beam and the Law of Equilibrium Acceleration in Circular Motion WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS To balance a beam around a pivot point, the principle of moments (or law of moments) is used. The law states that for a beam in equilibrium, the sum of clockwise moments about any point equals the sum of anticlockwise moments about the same point. This principle is essential for designing and understanding the equilibrium of lever systems and other balanced structures. Conditions for Equilibrium An object is in equilibrium if: The sum of all forces acting on it equals zero (static equilibrium). The sum of all moments (clockwise and anticlockwise) around any point is zero (rotational equilibrium). Centre of Gravity The centre of gravity (or centre of mass) of an object is the point through which the entire weight of the object acts. It behaves as if all the mass were concentrated at this single point. For a uniform object, such as a ruler, the centre of gravity is at its geometric centre. The stability of an object depends on the position of its centre of gravity relative to its base. An object is stable if its centre of gravity remains over its base of support. Toppling occurs when the vertical line through the centre of gravity falls outside the base of support. Increasing the base area and lowering the centre of gravity improves stability. Types of Equilibrium Stable Equilibrium: An object returns to its original position when displaced slightly (e.g., a ball in a bowl). Unstable Equilibrium: An object moves further away from its original position when displaced slightly (e.g., a ruler balanced on its edge). Neutral Equilibrium: An object remains in its new position when displaced (e.g., a ball sitting on a flat surface). Determining the Centre of Gravity Finding the centre of gravity of an irregularly shaped lamina involves suspending the object from different points and using a plumb line to mark the vertical line through which it hangs. The centre of gravity is where these lines intersect. Momentum Momentum (p) is the product of an object's mass (m) and its velocity (v ). Mathematically, p = mv It is a vector quantity, meaning it has both magnitude and direction. The SI unit of momentum is kilogram metre per second (kgm/s) or newton second (N s). Conservation of Momentum Stability and Toppling WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS The total momentum of a closed system of objects remains constant if no external forces act on it (such as friction or air resistance). This principle is known as the conservation of momentum. Momentum is conserved in collisions (both elastic and inelastic) and explosions. For example, in a collision, the total momentum before and after the collision remains the same. pinitial = pfinal Example: A trolley of mass m1 = 3 kg moving with velocity u1 = 5 m/s collides and couples with a stationary trolley of mass m2 = 2 kg. They move off together with the same velocity (v). We need to find (v). 1. Calculate initial momentum (pinitial ): pinitial = m1 ⋅ u1 = 3 kg ⋅ 5 m/s = 15 kgm/s 2. Calculate final momentum (pfinal ): Since they move off together with velocity (v): pfinal = (m1 + m2 ) ⋅ v = (3 kg + 2 kg) ⋅ v = 5 kg ⋅ v 3. Apply conservation of momentum (pinitial = pfinal ): 15 kgm/s = 5 kg ⋅ v 4. Solve for (v): = 3 m/s v = 15 5kgm/s kg So, the velocity (v ) of the two trolleys moving together after the collision is 3 m/s 1.6. Energy, work and power Types of energy stores Chemical Energy: Energy stored in chemical bonds of substances like food, fuels (oil, gas, coal, wood). Gravitational Potential Energy: Energy an object possesses due to its position relative to a reference point (usually the Earth's surface). Elastic Strain Energy: Energy stored in an object when it is compressed, stretched, or deformed. Kinetic Energy: Energy possessed by a moving object. Electrostatic Energy: Energy stored in charged objects due to their separation in an electric field. Nuclear Energy: Energy stored in the nucleus of an atom.. Internal (Thermal) Energy: Total energy stored in the microscopic motions and interactions of particles within a substance. Impulse Impulse (J ) is the change in momentum (Δp) of an object when a force acts on it over a period of time (Δt). Mathematically, J = F Δt = Δp Impulse is also a vector quantity and has the same direction as the force causing it. Energy Transfers Mechanical Working: Transfer of energy by the action of a force, like lifting a weight. Electrical Working: Transfer of energy by an electric current, such as in batteries or electric motors. Waves (Electromagnetic and Sound): Transfer of energy through waves, like light or sound waves. Heating: Transfer of energy through thermal processes, like heating water in a boiler. Principle of Conservation of Energy Energy cannot be created or destroyed, only transformed from one form to another. Thus the total amount of energy is constant. Energy Forms Force and Momentum: Relation of force to the rate of change of momentum: (F = Δp Δt ), which is an alternative form of Newton's second law. WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Kinetic Energy (Ek ): Energy possessed by an object due to its motion. Ek = 12 mv 2 , where (m) is mass and (v) is velocity. Example Calculation: For a football of mass 0.4 kg moving at 20 m/s: Ek = 12 × 0.4 × (20)2 = 80 J Potential Energy (Ep ):Energy an object has due to its position or condition or configuration. Ep = mgh , where (m) is mass, (g ) is acceleration due to gravity, and (h) is height. Example Calculation: For a 0.1 kg mass raised vertically by 1 m: Ep = 0.1 × 9.8 × 1 = 0.98 J Energy Type Renewable or Non-renewable Fossil Fuels Non-renewable Nuclear Fuels Non-renewable Solar Energy Renewable Wind Energy Renewable Wave Energy Renewable Tidal Energy Renewable Hydroelectric Energy Renewable Geothermal Energy Renewable Biofuels Renewable Work Work (W ) is done when a force (F ) displaces a body through a distance (d) in the direction of the force. Formula: W = F ⋅ d Unit: The unit of work is the joule (J), where 1 J = 1 N ⋅ m Example Calculation If a force of 50 N is used to move a crate 3 m horizontally: W = 50 N × 3 m = 150 J If lifting a mass of 3 kg vertically by 2 m (where g ≈ 10 m/s2 ): W = 30 N × 2 m = 60 J Energy resources Advantages Disadvantages High energy density, readily available during peak demand. Limited supply, environmental pollution (CO2, SO2), finite resource. Radioactive waste disposal High energy output, low issues, potential for CO2 emissions. accidents (e.g., Chernobyl, Fukushima). Abundant, no emissions Intermittent availability, high during operation, diverse initial costs for large-scale applications. installations. Clean energy source, Visual and noise impacts, abundant in suitable intermittent nature of wind. locations. Renewable, predictable in Technologically challenging, coastal areas with potential environmental consistent waves. impacts. Predictable and consistent, High infrastructure costs, minimal greenhouse gas environmental impacts on emissions. marine ecosystems. Disruption of aquatic Reliable, long operational ecosystems, potential life, minimal greenhouse displacement of gas emissions. communities, limited suitable sites. to geologically active Reliable, low emissions, Limited areas, high upfront costs for constant energy source. exploration and drilling. Renewable, lower emissions compared to fossil fuels. Competition with food production, land use issues, varying energy content. How Fossil Fuels are used in Power Stations Coal: In coal-fired power stations, coal is burned in a boiler to produce heat. Natural Gas: In gas-fired power stations, natural gas is burned directly in a gas turbine. The heat generated from burning these fuels is used to boil water, creating high-pressure steam. The steam drives turbines connected to electrical generators. Turbines are designed with sets of blades (rotor) mounted on a shaft, which rotates when steam is directed onto them. As steam expands through the turbine, its energy is transferred to the rotor, causing it to spin. The spinning rotor generates electricity through electromagnetic induction in the generator. How hydroelectric power stations work They run using the kinetic energy generated from the flow of water moving downstream. This kinetic energy spin turbines which are connected to generators. These generators then produce electricity that can be used by households. How Nuclear Fuels (uranium) are used in Power Stations WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Nuclear power stations use controlled nuclear fission reactions with uranium to generate heat. This heat is used to produce steam indirectly through a heat exchanger. The steam, similar to fossil fuel stations, drives turbines connected to generators to produce electricity. The operation involves the steam passing through a turbine's fixed blades (stator) onto the rotating blades (rotor), where the expansion of steam energy is converted into rotational motion. The rotational motion of the rotor then drives the electrical generator, producing electricity for consumption. Power The power of a device is the work it does per second, or the rate at which it does work. Power also represents the rate at which energy is transferred from one store to another. Formula: work done power = time taken W P = t where W is the work done in time t P = ΔE t where ΔE is the energy transferred in time t Key definition: Power is the work done per unit time and the energy transferred per unit time. Unit of power: watt (W ), where 1 W = 1 J/s Larger units: 1 kW = 1000 W = 103 W 1 M W = 1,000,000 W = 106 W Example: If a machine does 500 J of work in 10 s, its power is: 500J 10s = 50W Work done on load = 300 J Calculate Efficiency: J Efficiency = ( 300 400 J ) × 100 = 75% Example b: Electric Drill Given: Power input to drill = 300 J/s Useful power output (excluding thermal losses) = 200 J/s Calculate Efficiency: J/s Efficiency = ( 200 300 J/s ) × 100 = 66.67% Sankey Diagrams Sankey diagrams are used to represent energy transfers and efficiencies visually. They show how input energy is divided into useful output energy and wasted energy. The width of the arrows in a Sankey diagram is proportional to the amount of energy they represent. A wide arrow represents a large amount of energy, while a narrow arrow represents a small amount. Efficiency 1.7. Pressure % Efficiency formula for energy Energy Output Efficiency (%) = ( Useful Total Energy Input ) × 100% % Efficiency formula for power Power Output Efficiency (%) = ( Useful Total Power Input ) × 100% Example a: Electric Motor Given: Pressure is the force per unit area. Formula: pressure = force area Key definition: Pressure is the force per unit area. Unit of pressure: pascal (P a), where 1 P a = 1 N /m² Greater area over which a force acts results in less pressure. Liquid Pressure Energy input = 400 J WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Pressure in a liquid increases with depth because the further down you go, the greater the weight of liquid above. Pressure at one depth acts equally in all directions. Pressure depends on the density of the liquid; the denser the liquid, the greater the pressure at any given depth. The change in pressure Δp at a depth Δh below the surface of a liquid with density ρ is determined by considering a horizontal area A. Force acting vertically downwards on area A equals the weight of the liquid column of height Δh and crosssectional area A above it. Volume of the liquid column: ΔhA Mass of the liquid column: m = ρΔhA (mass = density × volume) Weight of the liquid column: mg = ρΔhAg Force on area A: ρΔhAg Pressure due to the liquid column: pressure = force area ρΔhAg = ρgΔh A Formula: Δp = ρgΔh Δp is the change in pressure beneath the surface of the liquid at depth Δh due to the weight of a liquid of density ρ g is the gravitational field strength This pressure acts equally in all directions at depth Δh and depends only on Δh and ρ. Value will be in pascals (P a) if Δh = is in meters (m) and (ρ) is in kilograms per cubic meter (kg/m³). 2. Thermal Physics WWW.ZNOTES.ORG 2.1. Kinetic Particle Model of Matter States of Matter Matter consists of tiny particles like molecules and atoms. Matter exists as solids, liquids, or gases, each with different characteristics. Solids have a definite shape and volume, and particles are close together in fixed positions. Liquids have a definite volume and take the shape of their container. The particles are further apart and can slide over each other. Gases have no definite shape or volume, and particles move much further apart and freely. Brownian Motion Describes random motion of particles in fluids (liquids and gases) and is caused by collisions with smaller, faster-moving particles. Temperature and kinetic energy Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Particles in solids vibrate in fixed positions at room temperature. Heating solids increases particle vibrations, raising their average kinetic energy. Cooling a solid reduces particle vibrations until absolute zero (-273°C or 0 K) stops all motion. Absolute zero is the lowest possible temperature achievable. Reducing the volume of a gas increases the concentration of particles. More particles per unit volume lead to more collisions with the container walls. The pressure increases proportionally to the decrease in volume: Variations in Gas Pressure with Volume Boyle's Law states that at constant temperature, the product of pressure and volume is constant: Pressure and Kinetic Energy Gases have particles moving randomly at high speeds. Each gas particle collision with a container wall changes its momentum, creating a force. The average force per unit area on container walls remains constant at a constant temperature. Increasing temperature raises collision frequency, increasing average force and gas pressure. Effect on Pressure of a Change in Temperature (Constant Volume) Heating a gas increases the kinetic energy of its particles. Higher kinetic energy leads to more frequent and energetic collisions with the container walls. Increased collisions result in higher pressure according to a gas law: ( PV = nRT ) Effect on Pressure of a Change in Volume (Constant Temperature) (p1 V1 = p2 V2 ) Graphing pressure ( p ) against the reciprocal of volume ( V1 ) gives a straight line. Absolute Zero and Kelvin Temperature Scale: Absolute zero, at −273°C or 0 K, is the lowest possible temperature. Kelvin scale temperatures are derived by adding 273 to Celsius temperatures: (T (K) = θ(°C) + 273) In the Kelvin scale, all temperatures are always positive and directly proportional to the average kinetic energy of particles. 2.2. Thermal properties and temperature Thermal expansion of solids, liquids and gases Solids and Liquids: When heated, particles vibrate more, causing them to push apart slightly, resulting in expansion. Gases: Heating increases particle speed and collisions with container walls, which causes container expansion to maintain pressure. Applications Bimetallic Strips: Made from metals with different expansion rates (e.g., copper and iron). Used in: Fire Alarms: Bends to complete an electrical circuit when exposed to heat, triggering alarms. Thermostats: Maintains temperature by bending to break or complete electrical circuits WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Shrink-fitting: Cooling components contracts them, fitting tightly into other parts upon warming. Used in manufacturing for tight connections without fasteners. Lid Removal: Expanding metal lids with hot water loosens them from glass jars, leading to easier opening. Precautions Expansion joints are spaces left between rail tracks used in railways, and pipes to allow for thermal expansion without damage Internal Energy and Heating Internal energy increases when an object is heated. Different materials require varying amounts of heat to raise their temperatures due to differences in specific heat capacity. Specific heat capacity (c) measures the amount of heat required to raise the temperature of a substance by 1 degree Celsius per unit mass. Specific heat capacity (c) is defined as the energy required per unit mass per unit temperature increase, measured in joules per kilogram per degree Celsius (J/(kg°C) The formula relating heat energy (ΔE ), mass (m), specific heat capacity (c), and temperature change (Δθ) is: \n ΔE = mcΔθ Specific heat capacity quantifies how much heat energy is needed to raise the temperature of a substance. Materials with higher specific heat capacities require more heat energy per unit mass to achieve the same temperature change. Worked Example Calculation Given: Heat energy supplied, (ΔE = 20000, J) Mass of the substance, (m = 5, kg) Temperature change, (Δθ = 10°C) Calculate the specific heat capacity (c) of the substance. Formula: The specific heat capacity (( c )) is given by: ΔE c = mΔθ Substituting the given values: c = 20000 5×10 Calculation: c = 20000 50 c = 400J/(kg°C) Temperature and Thermal Energy Temperature is related to the average kinetic energy of particles. Thermal energy is the total energy of particles in a substance, and more particles can hold more total thermal energy even if they have lower individual particle energies. Heat Transfer and Equilibrium Heat transfers from higher to lower temperature bodies until thermal equilibrium is reached. This transfer is caused by collisions between particles, making their average kinetic energies equal. Specific Heat Capacity WWW.ZNOTES.ORG Change of State Heating can change a solid to a liquid (melting) and a liquid to a solid (freezing). Pure substances melt and freeze at specific temperatures, such as water at 0°C. Melting involves particles of a solid overcoming intermolecular forces to become a liquid. Solidification (freezing) involves the transfer of potential energy from particles to surroundings as a liquid becomes solid. Vaporisation requires substantial energy to overcome intermolecular forces in a liquid to become gas (vapour). Condensation involves gas particles losing potential energy to their surroundings as they return to a liquid state. Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Convection Evaporation Higher temperatures, larger surface areas, and wind or draughts increase the rate of evaporation. Energy is transferred to the surroundings from the liquid during evaporation, cooling the liquid. Evaporation cools the body through sweat, helping to maintain a constant temperature. Differences between boiling and evaporation Feature Temperature Process Energy Requirement Speed Throughout Liquid? Boiling Evaporation Occurs at a specific boiling Occurs at any temperature below temperature. the boiling point. Bubbles of vapour form within the Occurs at the surface of the liquid. liquid. Requires sufficient heat to reach Requires less heat and occurs due to boiling point. energetic particles escaping. Rapid compared to evaporation. Slower compared to boiling. Happens throughout the entire Happens only at the liquid's surface. volume of the liquid. Heat transfer method in fluids like liquids and gases. Transfer of thermal energy by movement of the matter itself. Convection Currents Warm fluids rise because they expand and become less dense. Cooler, denser fluids sink and replace the rising warm fluid. This movement of fluids due to temperature differences is known as a convection current. 2.3. Transfer of thermal energy Conduction Conduction is heat transfer through matter from hot to cold without moving matter. Metals conduct heat well (e.g., copper, aluminum); insulators (wood, plastic) are poor conductors. Metals feel colder due to rapid heat transfer from the hand compared to insulators at the same temperature. Liquids and gases conduct heat slowly because the particles are further apart and need time to transfer energy to each other. Metals transfer heat via fast-moving free electrons, raising temperatures in cooler areas and lattice vibrations. Non-metals transfer heat through slower atomic or molecular vibrations, lacking free electrons. Radiation A method of thermal energy transfer which occurs without matter, even in vacuum. Emits as electromagnetic waves, travels at speed of light. Absorption and Reflection Surfaces vary in radiation absorption. Black surfaces absorb more than shiny white ones. Emission Surface Type Shiny White Dull Black WWW.ZNOTES.ORG Absorption of Radiation Poor absorber Good absorber Emission of Radiation Poor emitter Good emitter Reflectivity High Low Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Surfaces emit radiation differently when hot. Dull black surfaces emit more than shiny surfaces. All bodies emit radiation above absolute zero. Greenhouse effect Greenhouse gases trap heat similar to glass in a greenhouse. Balance between incoming solar radiation and emitted Earth radiation crucial for climate stability. Increased carbon dioxide and methane upset this balance and absorb more infrared which cannot escape. Wavelength (λ): Distance between 2 successive crests/ troughs. Frequency (f ): Number of complete waves created per second, measured in hertz (Hz). Wave speed (v): Distance moved by a crest or any point on the wave in 1 second. Amplitude (a): Height of a crest or depth of a trough from the undisturbed or mean position. Phase: Particles in ‘phase’ have the same speed and direction of vibration. Wave equation Faster vibration produces a shorter wavelength. Therefore, a higher frequency results in a smaller wavelength. Wave equation: v = fλ Wavefronts and rays Wavefront: A straight line where the wave has the same phase at all points. Ray: Line drawn at right angles to a wavefront showing the direction of travel. 3. Waves 3.1. General Properties of Waves Progressive waves carry energy from one place to another without transferring matter. Two Types of Progressive Waves Transverse waves Longitudinal waves Reflection of a wave at a plane surface WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Straight water waves (transverse waves) hit a metal strip in a ripple tank at x° angle. Angle of incidence (i) and angle of reflection (r)are both x° . Angle of incidence equals angle of reflection: (i = r) Same wavelength as reflected wave Same wave speed Straight water waves meet narrow gaps and create circular wavefronts. Diffraction can also occur at the edges of obstacles causing wave spreading. 3.2. Reflection and Refraction of Light Refraction Continuous straight waves in shallow water have shorter wavelengths than in deeper water. Waves in shallower water have a smaller speed and smaller wavelength. When waves move from shallow to dense regions, they bend towards the normal, and when they move from dense to shallow regions, they bend away from the normal. Light travels in a path called a ray. A beam is a stream of light shown by several rays. Beams can be parallel, diverging, or converging. Speed of Light The speed of light is about 1 million times faster than the speed of sound. The speed of light is 3 × 108 meters per second. Reflection of light against a plane mirror Diffraction The normal is perpendicular to the mirror at the point where the incident ray strikes. The angle of incidence (i) is between the incident ray and the normal. The angle of reflection (r) is between the reflected ray and the normal. The law of reflection states that the angle of incidence is equal to the angle of reflection. WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Light refracts due to speed change when entering a different medium. In air, light travels at 300, 000 km/s (3 × 10⁸ m/s) In glass, it slows to 200,000 km/s (2 × 10⁸ m/s) Refractive index (n) is the ratio of light speed in air to light speed in the medium. For glass: n = 300,000km/s = 32 = 1.5 200,000km/s Refractive index is the ratio of speeds of a wave in two different regions. sin(i) Experimentally it is true that n = sin(r) where (i) is the angle in air and (r) is the angle in glass. Higher refractive index means greater bending of light as it slows down more. Real and Virtual Images A real image can be produced on a screen and is formed by rays that pass through the screen. A virtual image cannot be formed on a screen. A virtual image is produced by rays that seem to come from it but do not pass through it. The image in a plane mirror is virtual. Rays from an object are reflected at the mirror and appear to come from a point behind the mirror where the rays would meet when extrapolated (extended) backward. Critical Angle When light passes from an optically denser to an optically less dense medium at small angles of incidence, there is a strong refracted ray and a weak reflected ray. Increasing the angle of incidence increases the angle of refraction. Critical angle (c) occurs when the angle of refraction is 90°. For angles of incidence greater than (c), light undergoes total internal reflection. Total internal reflection means that the light does not cross the boundary and reflects inside the denser medium. For the critical angle: sin(c) = n1 where n is the refractive index. Refractive Index 3.3. Lenses Converging and Diverging Lenses WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS A converging (or convex) lens is thickest in the center and bends light inwards. A diverging (or concave) lens is the thinnest in the center and spreads the light out. The center of a lens is its optical center (C) and the line through C at right angles to the lens is the principal axis. Draw a straight line (parallel to the principal axis). Start the line from the top of the object towards the lens. After refraction through the lens, draw this direct ray through the focal point F on the opposite side of the lens. Principal focus When a beam of light (parallel to the principal axis) passes through a converging lens, it refracts to converge at a point called the principal focus (F ). The principal focus of a converging lens is a real focus. A diverging lens has a virtual principal focus behind the lens, from which the refracted beam appears to diverge. A lens has two principal focuses, one on each side, each equidistant from the optical center (C). The distance (CF ) is the focal length (f ) of the lens. Central Ray (Ray 2): Draw a straight line from the top of the object through the optical center C of the lens. This ray will continue in the same direction without bending at all. Image formed: Ray diagrams A ray parallel to the principal axis is refracted through the principal focus (F ). A ray through the optical center (C) is undeviated (not refracted) for a thin lens. A ray through the principal focus (F ) is refracted parallel to the principal axis. The intersection of rays (in one beam) after refraction gives the location of the image. How to draw a ray diagram step-by-step Parallel Ray (Ray 1): These two will intersect on the opposite side of the lens to form the image of the object. Magnification The linear magnification (M ) is given by: image size M = object size Magnification can also be expressed as: distance of image from lens M = distance of object from lens Image properties at different object positions are shown below: WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Object Position At 2F Between 2F and F At F Between F and lens Image Position At 2F Beyond 2F At infinity On the same side of lens Image Nature Real, inverted Real, inverted Real, inverted Virtual, upright Image Size Same size Larger Infinitely large Larger When white light passes through a triangular glass prism, it separates into a band of colors known as a spectrum. This separation of colors is called dispersion and occurs because the refractive index of glass varies with the wavelength of light. White light consists of many colors with different wavelengths, and the prism separates them based on their refractive indices. The colors of the visible spectrum, from longest to shortest wavelength, are: red, orange, yellow, green, blue, indigo, and violet Red light, with the longest wavelength and lowest frequency, is refracted the least by the prism. Violet light, with the shortest wavelength and highest frequency, is refracted the most by the prism. Applications of Lenses in Vision Correction Short-Sightedness (Myopia) Cause: The eye lens focuses light in front of the retina instead of on it. This causes distant objects to appear blurry. Correction: A diverging (concave) lens is used to spread out light rays before they enter the eye, so the lens can focus them correctly on the retina. Long-Sightedness (Hypermetropia) Cause: The eye lens focuses light behind the retina. This causes nearby objects to appear blurry. Correction: A converging (convex) lens is used to focus light rays closer together before they enter the eye, so they focus correctly on the retina. 3.4. Dispersion of Light Refraction by a Prism In a triangular glass prism, a ray bends due to refraction at each surface. The bending at the first surface combines with the bending at the second surface. This combined change in direction is called the deviation. Unlike in a parallel-sided block, where the emergent (exiting) ray remains parallel to the incident ray, these bendings do not cancel out in a prism. 3.5. Electromagnetic Spectrum Light waves and Electromagnetic Spectrum Light is part of the electromagnetic spectrum, which extends beyond visible light in both directions (with greater wavelength vs. smaller wavelength) The spectrum includes gamma rays, X-rays, ultraviolet, infrared, microwaves, and radio waves. Wavelength increases from gamma rays to radio waves, while frequency increases from radio waves to gamma rays. Properties of Electromagnetic Waves Dispersion WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Electromagnetic waves travel at the speed of light in a vacuum, approximately 3 × 108 m/s. They can undergo reflection, refraction, and diffraction and are transverse waves. They follow the wave equation v = f λ, where (v ) is the speed of light, (f ) is the frequency, and (λ) is the wavelength. Higher frequency means smaller wavelength and therefore more energy carried. Radio Waves and Microwaves Radio waves are the longest-wavelength electromagnetic waves used for communication, radio and television transmission, astronomy, and radio frequency identification. Microwaves have shorter wavelengths than radiowaves and are used in telecommunications, satellite communication, radar, and microwave ovens. X-rays have smaller wavelengths than ultraviolet rays and are used in medical imaging, security screening, and industrial inspection. Gamma rays are highly penetrating (smallest wavelength and largest frequency) and used in cancer detection cancer treatment to kill cells, sterilization, and material inspection. Communication Systems Below are the differences between digital and analog signals: Aspect Digital Signals Signal Type Discrete, binary (0s and 1s) Transmission Rate Examples Higher transmission rates Digital data, internet signals, computer memory Analog Signals Continuous, varying amplitude and frequency Limited by bandwidth and signal degradation over distance Audio signals, analog television, older telephone systems Infrared Radiation Detected as heat by the body; used in thermal imaging, heating, and remote controls. Also used in communication (optical fibers), electric grills, and intruder alarms. However, high-intensity infrared can cause burns and eye damage. Visible Light Red light has the longest wavelength, and violet light has the shortest. Monochromatic light consists of one color (single frequency), where frequency is more responsible than wavelength to express the colour. Visible light enables vision and is used for illumination and photography. Optical instruments like microscopes and telescopes use light properties to form images. Infrared Optical Fibers Infrared optical fibers use the principle of total internal reflection to make infrared or light travel along the fiber without much loss. Used for long-distance data transmission, offering high bandwidth and low signal loss compared to electrical transmission. Ultraviolet Radiation Shorter wavelengths than visible light; causes sunburn and skin damage. Used in fluorescent applications (e.g., security marking, water treatment, artificial skin-tanning) and sterilising water. Can be harmful in high doses. X-rays and Gamma Rays WWW.ZNOTES.ORG 3.6. Sound Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Longitudinal Waves Sound waves are longitudinal Particles in the medium (like air or water molecules) vibrate back and forth parallel to the direction of wave propagation. This creates areas of compression (where molecules are closer together) and rarefaction (where they are far apart) as the wave travels through the medium. The movement of particles transfers energy through the medium. This vibration causes the sound to be heard Compressions and Rarefactions Humans can only hear sound frequencies ranging from about 20Hz (low pitch) to 20,000Hz (high pitch). The upper limit of audibility decreases with age due to changes in the sensitivity of the ear. Audibility can also be affected by the intensity (loudness) of the sound which is determined by amplitude. Reflection of sound (Echo) Sound waves reflect off hard and flat surfaces like how light reflects off a mirror. When sound reflects, it creates an echo, which is a repetition of the original sound heard after a short delay. Sound waves are made of compressions (C ) and rarefactions (R) as they move through a medium. Compressions are regions where air molecules are densely packed together and the regions have higher pressure. Rarefactions are regions where air molecules are less densely packed and the regions have lower pressure. Speed of Sound Frequency and Wavelength Frequency (f ) of a sound wave is the number of complete wave cycles per second and is measured in Hertz (Hz ). Higher frequencies mean higher-pitch sounds, while lower frequencies mean lower-pitch sounds. Wavelength (λ) is the distance between two consecutive compressions or rarefactions in a sound wave. The speed of sound (v ) in a medium is determined by the product of its frequency and wavelength: (v = f λ). The speed of sound in air is approximately 330–350 meters per second (m/s) at room temperature. In other materials, such as water (with a speed of approx. 1500m/s) or steel (with a speed of approx. 5100 m/s), the speed of sound may vary due to differences in the density. Temperature affects the speed of sound in air and it increases with temperature because warmer air molecules move faster. Measurement of the Speed of Sound Limits of hearing WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Echo Method Stand at a known distance (like more than 300 meters) from a large wall. Clap hands or produce a sharp sound and start a stopwatch simultaneously. Wait for the distinct echo from the surface and stop the stopwatch when you hear it. Calculation: Use the formula (v = 2dt ), where (d) is the distance to the surface and (t ) is the time interval measured with the stopwatch. The pitch of the note is determined by the frequency of the sound wave (higher frequencies produce higher pitch notes). Loudness is determined by the amplitude of vibrations ( greater amplitude produces louder sounds) Quality (timbre) of a sound is its unique shape or texture, caused by the instrument's construction. Note: Twice the distance is used because the sound travels away from you and then back again, covering the entire distance two times. Direct Method Place two microphones a known distance (like 10 meters) apart. Connect microphones to an oscilloscope to detect the sound. Produce a sound source equidistant from both points and start timing when the sound is produced. Stop timing when the sound is detected at the second point. Use the formula (v = dt ), where (d) is the known distance between the two microphones and (t) is the measured time interval between detection at the two points. Ultrasound Ultrasound refers to sound waves with frequencies above the upper limit of human hearing (> 20, 000Hz ). It is used in medical imaging and industrial applications for precision and non-destructive testing. Ultrasound waves behave similarly to audible sound waves but can penetrate materials and provide detailed imaging without harmful effects. 4. Electricity and Magnetism 4.1. Simple Phenomena of Magnetism Magnetic Materials Musical Notes WWW.ZNOTES.ORG Ferromagnetic materials like iron can be made into magnets. Magnetic materials are naturally attracted to magnets even when not magnetized.. Magnetic Poles Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Magnetic poles attract magnetic materials and are found near the ends of magnets. Poles always come in pairs: north and south. Every magnet has a North Pole (N ) and a South Pole (S ). The North Pole of a magnet points towards the Earth's geographic North Pole. Law of Magnetic Poles Similar poles (N − N or S − S ) repel each other. Opposite poles (N − S ) attract each other. The attraction or repulsion decreases as poles move farther apart. Iron nails and steel paper clips can be magnetised by hanging them from a magnet. Each nail or clip magnetises the next in a chain, with unlike poles attracting each other. Removing an iron chain by pulling the top nail causes it to collapse because iron shows temporary magnetism. Steel chains do not collapse when removed because they have permanent magnetism. Soft materials (e.g. iron) are easily magnetised but lose magnetism quickly. Hard materials (e.g. steel) are harder to magnetise but remain magnetised longer. Induced Magnetism Magnetic materials can become magnetized when near a magnet. Magnetisation of Iron and Steel Magnetic and Non-magnetic Materials Magnetic materials (iron, steel, nickel, cobalt) are attracted to magnets and can be magnetised. Non-magnetic materials (e.g., aluminium, wood) are not attracted to magnets and cannot be magnetised. Magnetic Fields WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS A magnetic field is the region around a magnet where magnetic forces act. Field strength is higher where magnetic field lines are closer together and lower where they are further apart. Magnetic fields are shown using lines of force, showing the direction from North to South poles. The density of these lines indicates field strength: closer lines represent stronger magnetic fields. Electromagnets They are formed from a coil of wire through which an electrical current passes. Magnetism is temporary and can be switched on and off, unlike permanent magnets. They contain a core of soft iron that only becomes magnetised when current flows through the coil. Factors Affecting Electromagnet Strength Current Increase: Higher current in the coil results in stronger magnetism. More Turns: Increasing the number of turns in coils around the core increases magnet strength. Closer Poles: Moving the magnetic poles closer together increases electromagnet strength. 4.2. Electrical quantities Electric Charge Like/same charges (+ and + or – and – ) repel, while unlike charges (+ and –) attract. Force Between Charges The force between electric charges decreases as their separation increases. Positive charges repel other positive charges and attract negative charges. Negative charges repel other negative charges and attract positive charges. Charges, Atoms, and Electrons Atoms consist of a central nucleus with protons (positive) and electrons (negative) orbiting around it. Protons and electrons have equal but opposite charges, making atoms electrically neutral overall. Production of Charges WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Charges are produced by friction, which transfers electrons between materials. Electrons move between materials during rubbing; protons remain in the nuclei and do not move. Units of charge Charge is measured in coulombs (C ) and defined in terms of the ampere (A) The charge on an electron is (e = −1.6 × 10−19 ) C . Electrons, Insulators, and Conductors Insulators: Electrons are firmly bound to atoms; rubbing can charge them statically. Conductors: Electrons can move freely; they require insulation to hold a charge. Type Insulators Conductors Description Electrons are firmly bound to atoms; rubbing can charge them statically. Electrons can move freely; require insulation to hold a charge. Examples Plastics (polythene, cellulose acetate), Perspex, nylon Metals, carbon Electric Fields When charges are near each other, they experience a force known as the electric force. Electric field is a region where a charge feels a force due to nearby charges. Uniform electric field exists between oppositely charged parallel metal plates, shown by evenly spaced lines perpendicular to the plates. The direction of the electric field is indicated by arrows, representing the force acting on a small positive test charge (pointing away from positive charges and towards negative charges). The Ampere and the Coulomb (units of current and charge) WWW.ZNOTES.ORG Electric Current is defined as charge passing a point per unit time, symbolized as (I = Qt ). Unit of current is the ampere (A), with one milliampere ( mA) equal to one-thousandth of an ampere and is measured by an ammeter. Unit of charge is the coulomb (C ), defined as the charge passing a point when a steady current of 1 ampere flows for 1 second (1C = 1As). Charge Calculation Q=I ×t where Q is charge, I is current, and t is time in seconds. Conventional Current Conventional current flows from positive to negative terminals of a battery, opposite to electron flow. Circuit diagrams show conventional current direction with arrows, while electrons move in the opposite direction. Direct and Alternating Current Direct Current (d.c.) Alternating Current (a.c.) Electrons flow continuously in one direction. Electrons regularly change their direction of flow. Provided by batteries Produced by generators. Frequency of Alternating Current Frequency refers to the number of complete cycles per second. It is measured in Hertz (Hz ), where 1 Hz equals one cycle per second. 4.3. Voltage, Resistance and Power Electromotive Force (e.m.f .) Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Chemical actions inside a battery produce electron excess at the negative terminal and shortage at the positive terminal Battery maintains electron flow (electric current) in a connected circuit as long as chemical actions last. The battery does work when moving the charge around the circuit. Electromotive force (e.m.f .) is the electrical work done by a source in moving unit charge around a complete circuit. Electromotive force is measured in volts (V ). Potential Difference Electric current transfers energy from a battery to circuit components and surroundings. Potential difference (p.d.) is the work done by unit charge passing through a component P .d. is measured in volts. Voltage is sometimes used instead of p.d. 1 volt = 1 joule per coulomb 1 V = 1 CJ ) Formula: V = W Q or W = Q × V Resistance Electrons move more easily through some conductors when p.d. is applied. Resistance is the opposition of a conductor to current. Good conductors have low resistance while poor conductors have high resistance Ohm (Ω) is the unit of resistance. Formula: R = VI They can change current in a circuit (rheostat mode) or act as a potential divider by dividing voltage across components as desired. Resistance depends on the length, cross-sectional area, and material of the wire Resistance increases with length but decreases with a larger cross-sectional area Formula: (R ∝ Al ) I–V graphs and Ohm’s Law Metals and some alloys give I–V graphs that are straight lines through the origin, showing that I is directly proportional to V or that I ∝ V . Doubling V doubles I . Such conductors obey Ohm’s law: V = IR Ohmic or linear conductors are the conductors where resistance does not change with V . Variable Resistors Semiconductor Diode WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Diode has small resistance when connected one way and very large resistance when p.d. is reversed. It conducts electricity in one direction only, and it is a non-ohmic conductor. Filament Lamp Non-ohmic conductor at high temperatures I–V graph curve flattens as V and I increase, showing increasing resistance with increasing current and increasing temperature. An increase in temperature generally increases the resistance of metals. Thermistors' resistance is different and decreases with rising temperature. It is a non-ohmic conductor Light-dependent Resistor (LDR) Resistance of some semiconductors decreases with increased light intensity. Light-dependent resistors (LDRs) use this property to function. I–V graph for an LDR is similar to that of a thermistor LDR is also a non-ohmic conductor. Power in Electric Circuits Power defined as work done or energy transferred per time taken: P = Wt P is power in watts (W ), W is work done in joules (J ), t is time in seconds (s) For a steady current (I) in a device with a potential difference (V ) across it, the work done has a formula W =I ×t×V Substituting work done with the power P = IV multiplied by time in seconds (t), the energy transferred is: E = Pt = IV t Thermistor Example Lamp with 240 V supply and 0.25 A current Power = P = IV = 240 V × 0.25 A = 60 W 60 J of energy transferred to the lamp each second Voltage in terms of power and current WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Volt can be defined as a watt per ampere: V = PI If all energy transferred to thermal energy in a resistor of resistance R: P = V × I = IR × I = I 2 R Doubling the current produces four times the thermal energy per second P = I 2 R Larger unit for energy: kilowatt-hour (kWh) 1 kWh = 1000 Js × 3600 s = 3600000 J = 3.6 M J The cost of electricity in houses is calculated by using kWh where each kWh has a fixed price and is multiplied by the units you consume. In a parallel circuit, components are connected side by side, providing alternative paths for current flow. The total current is the sum of the currents through each branch If the total current from the source is (I0 ), and the current through each branch is I1 , I2 and I3 then I0 = I1 + I2 + I3 4.4. Electric Circuits Electrical component symbols Potential Difference (p.d.) in Series and Parallel Circuits In a series circuit, the total potential difference across the components is the sum of the individual potential differences: V0 = V1 + V2 + V3 In a parallel circuit, the potential difference across each component is the same as the potential difference across one branch: Vacross each branch = V0 Current in a Series Circuit In a series circuit, there is a single path for the current to flow. The current remains the same throughout: Current (I ) is consistent at every point in the series circuit. The reading on an ammeter will be identical no matter where it is placed in the circuit. Current in a Parallel Circuit Cells, Batteries, and Electromotive Force (e.m.f .) Cells in series increase the total e.m.f . of the battery. For example, if two 1.5 V cells are connected in series then the e.m.f .= 1.5 V + 1.5 V = 3.0 V Resistors in Series In a series circuit, the total resistance (R0 ) is the sum of the individual resistances: R0 = R1 + R2 + R3 Given resistors R1 , R2 , and R3 the total voltage (V ) across them is: V = I × R Worked Example WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS For a 4.5 V battery across resistors of 3 Ω, 4 Ω and 5 Ω in series: Combined resistance: R0 = R1 + R2 + R3 = 3 Ω + 4 Ω + 5 Ω= 12 Ω Current (I ): I = VR = 4.5V 12Ω = 0.375 A p.d. across 4 Ω resistor: V2 = I × R2 = 0.375 A × 4 Ω = 1.5 V Resistors in Parallel The combined resistance (R0 ) of resistors in parallel is given by: R10 = R11 + R12 + R13 … Two resistors R1 and R2 have resistance of R10 = R11 + R12 1 ×R 2 = R0 = R R 1 +R 2 In a thermistor, resistance decreases with increasing temperature. When it’s used in a potential divider circuit: As temperature rises, the thermistor's resistance decreases. This lowers the combined resistance of the two resistors, increasing the current if the supply voltage remains constant. The potential difference across the fixed resistor increases relative to that across the thermistor. A variable resistor can also act as a potential divider by adjusting the position of the contact, changing the output potential difference. Properties of Parallel Circuits 1. The current from the source is greater than the current in each branch. 2. The combined resistance of parallel resistors is less than that of any individual resistor. 4.5. Applications of electric circuits Increase in Resistance of a Conductor In metals, current is carried by free electrons. As the temperature of the metal increases: The atoms vibrate more, making it harder for electrons to move. This results in an increase in resistance. Potential Divider For two resistors R1 and R2 in series with a supply voltage (V ): The total current (I) is given by: I = R1 V+R2 From Ohm's Law V = IR , if resistance (R) increases while maintaining a constant current(I), the potential difference ( V ) across the conductor also increases. Variable Potential Divider WWW.ZNOTES.ORG Light-Dependent Resistor (LDR) Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS An LDR’s resistance decreases with increasing light intensity. In a circuit, as light intensity increases: The LDR’s resistance decreases, allowing more current to flow. This increase in current can light a lamp or cause other actions. A relay allows a small current to control a larger current needed to operate an appliance. In a switching circuit: If the switching circuit output is high, a small current flows through the relay, closing the mains switch. This isolates the low voltage circuit from the high voltage mains supply. Light-Emitting Diode (LED) An LED emits light when forward-biased (cathode connected to the negative terminal): Reverse bias (anode connected to the negative terminal) does not emit light and can damage the LED if the reverse voltage exceeds 5 V . A suitable resistor R (e.g. 300 Ω on a 5 V supply) is needed to limit the current. Semiconductor Diode Thermistor A thermistor's resistance decreases significantly with temperature increase. In a series circuit with a thermistor: As temperature rises, its resistance drops, decreasing the potential difference across it. This causes an increase in voltage across a series resistor, which can trigger a relay or alarm. A diode allows current to pass in only one direction: Forward-biased: current flows when the anode is connected to the positive terminal and the cathode to the negative terminal. Reverse-biased: the diode does not conduct and has high resistance. 4.6. Electrical safety Dangers of Electricity Relays WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Damaged Insulation: Exposes wires, increasing shock and fire risk. Overheated Cables: Can lead to fire. Damp Conditions: Increase shock severity due to reduced resistance. Excess Current: From overloaded plugs, extension leads, and multiple sockets. Electric Shock: Current flows from an electric circuit through a person's body to earth. Dry Skin: Resistance ~10,000 Ω and current around 24 mA (it is safe). Wet Skin: Resistance ~1,000 Ω and current ~240 mA (can be deadly). Larger currents are more dangerous. Longer exposure increases risk. Reducing Risk Turn off power before repairs. Use earth pin and cord grips. Keep appliances dry and away from water. Avoid trailing cables and damage, especially with cutting tools. First Aid for Electric Shock Switch off the power if the person is still in contact with the equipment. Call for medical assistance. Causes of fires Flammable materials near hot appliances or wiring. Overheated wiring produces excessive current and can lead to fire. Preventive Measures: Match fuse rating to appliance. Do not overload sockets or use too many adapters. Use thick wires for high-power appliances. House Circuits Live and Neutral Wires: Both supply electricity and the neutral is earthed. Earth Wire: Provides safety by connecting metal cases to earth. Switches and Fuses Switches and fuses are in the live wire to prevent shocks. Fuse breaks the circuit if the current exceeds safe levels. Circuit Breakers Electromagnetism breaks the circuit when current exceeds a preset level. Advantages: Faster operation and can be reset. Earthing Prevents shock by providing a path for fault currents. Earth pin connects appliance metal cases to earth, preventing them from becoming live. Double Insulation Appliances with two layers of insulation don’t need an earth wire. 4.7. Electromagnetic induction Process of generating electricity from a changing magnetic field. Electromagnetic Induction Experiments WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Straight Wire and U-shaped Magnet Wire held still between magnet pole leads to no induced current. Moving wire vertically (up or down) between poles induces current because of changing magnetic flux (cutting magnetic field lines) Upward movement: current flows in one direction. Downward movement: current flows in the opposite direction. Deflection on meter is temporary and occurs only while wire is moving. Inserting magnet into coil (solenoid) induces current in one direction. A solenoid is a coil of wire wound in a helical shape that generates a magnetic field when an electric current passes through it. Removing magnet from solenoid induces current in the opposite direction. No current is induced when magnet is stationary inside solenoid. Current direction reverses with the direction of magnet movement. This also works if the solenoid is moved instead of the magnet. Factors Affecting Induced e.m.f . Bar Magnet and Coil (solenoid) Faster movement of magnet or coil increases induced e.m.f. More turns in the coil increase the induced e.m.f. Stronger magnets increase the induced e.m.f. e.m.f . is directly proportional to the rate at which the conductor cuts through magnetic field lines. Direction of Induced e.m.f . (Lenz’s Law) Induced e.m.f . always opposes the change causing it. If a magnet approaches a coil, the induced current generates a magnetic field that opposes the motion. If a magnet is withdrawn, the coil’s induced current generates a field that attracts the magnet. Magnetic Fields WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Straight Wire: When current flows through a vertical wire, iron filings around it form circles. Meaning that around a straight wire, there are circular magnetic field lines. Field direction changes with current direction (upwards or downwards through the wire) Use right-hand grip rule: direction of thumb (upwards or downwards) indicates magnetic field direction by the remaining fingers (clockwise or anti-clockwise). Variation of Magnetic Field Strength Magnetic field strength decreases with distance from the wire. Field lines spread out as distance increases. Increasing current strengthens the magnetic field and lines become closer together. Reversing current direction reverses the direction of the magnetic field. 4.8. Applications of electromagnetic effects Relay Solenoid A long cylindrical coil produces a magnetic field similar to a bar magnet. End A behaves like the north pole, and end B behaves like the south pole. Right-hand grip rule: grip solenoid in current direction, thumb points to the north pole. Magnetic field inside the solenoid is stronger and denser compared to outside. A relay is a switch that operates using an electromagnet. It allows one circuit to control another When current flows through the coil, it magnetizes the soft iron core. The magnetized core attracts the L-shaped iron armature. The armature rocks on its pivot and closes contacts in another circuit. Components Coil: Creates the magnetic field. Soft Iron Core: Magnetized by the coil, attracts the armature. L-shaped Iron Armature: Moves to close or open contacts. Contacts: Switches the second circuit on or off. Reed Switch WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS A reed switch uses magnetic fields to control a circuit. Operated by current flowing through a coil, which magnetizes reeds of magnetic material. Current flows: Reeds become magnetized, attract each other, and close the circuit. Current stops: Reeds lose magnetization, separate, and open the circuit. A device that produces sound by ringing is an electric bell Pressing the bell push completes the circuit. Current flows through electromagnet coils, magnetizing them. Electromagnet attracts a soft iron bar (armature), causing the hammer to hit the gong. The circuit breaks at contact screw point Electromagnet loses magnetism, armature returns to its original position. The springy metal strip reconnects the circuit, and the cycle repeats as long as the bell push is pressed. Loudspeaker It converts electrical signals into sound waves. Varying currents pass through a coil placed in a magnetic field. Magnetic fields interact, causing the coil to vibrate. A paper cone attached to the coil moves with it. Vibrations create sound waves in the surrounding air. Components Coil: Receives electrical signals and vibrates. Magnet: Provides the magnetic field for interaction. Paper Cone: Moves with the coil to produce sound. 4.9. Motors and generators Simple d.c. Electric Motor Electric Bell WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Components Rectangular coil: Fixed up on an axle that can rotate. C-shaped magnet: Provides the magnetic field. Split-ring commutator: A copper ring split into two halves, connected to the ends of the coil. It rotates with the coil. Brushes: Carbon blocks pressed against the commutator to supply current continuously. Fleming’s Left Hand Rule is used for the d.c. motor The a.c Generator Components Operation When direct current (d.c.) flows through the coil, a force acts on the coil due to the interaction with the magnetic field. This force creates a turning effect, causing the coil to rotate. The split-ring commutator reverses the direction of current in the coil as it rotates, making sure there is continuous rotation by maintaining the direction of force. Rectangular coil: Positioned between the poles of a Cshaped magnet. Slip rings: Connected to the ends of the coil, rotate with the coil. Carbon brushes: Press against the slip rings to conduct current. Operation WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS As the coil rotates in the magnetic field, it cuts through the field lines, inducing an electromotive force (e.m.f .) The e.m.f . varies as the coil moves Vertical Position: No e.m.f . as the coil cuts the least number of field lines. Horizontal Position: Maximum e.m.f . as the coil cuts the most field lines. The direction of e.m.f . reverses as the coil continues to rotate, producing alternating current (a.c.) in the circuit. The frequency of the a.c. is determined by the rotation speed of the coil. For example, a coil rotating twice per second generates an a.c. with a frequency of 2 Hz. This occurs when current changes in one coil, inducing a voltage in a neighboring coil. Magnetic field lines from the primary cut through the secondary coil, inducing voltage. Induced voltage increases with a soft iron rod or complete iron ring core due to increased magnetic field lines. Fleming’s Right Hand Rule is used for the a.c. generator. Transformer Equation The alternating voltage applied to the primary induces an alternating voltage in the secondary. V N Relationship given by Vps = Nps Vp and Vs the primary and secondary voltages. Np and Ns are the primary and secondary turns. Step-up transformer: More turns are on secondary (Vs > Vp ). Step-down transformer: fewer turns on secondary, ( Vs < Vp ). 4.10. Transformers The transformer changes alternating voltage to different values. Consists of primary and secondary coils on a soft iron core. Coils can be wound on top of each other or separate limbs. Mutual Induction Worked Example A transformer steps down the mains supply from 230V to 10V. N 23 Turns ratio: Nps = 230V 10V = 1 If the secondary has 80 turns, the primary has 80 × 23= 182 turns. Energy Losses WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS If V s stepped up, current I is stepped down proportionally. Ideal transformer (100% efficient): Ip Vp = Is Vs Ip and Is are primary and secondary currents. If V is doubled, I is halved. 5. Nuclear Physics 5.1. Nuclear model of the atom Current atomic model The nucleus of an atom consists of protons and neutrons. Three basic particles in an atom include protons, neutrons, and electrons. Proton = a hydrogen atom minus an electron charge +1, mass about 2000 times that of an electron. Neutron: Uncharged and with a mass almost equal to that of a proton. Relative charges: Proton = +1 and neutron = 0 while electron = -1. Protons and neutrons are located in the nucleus and are together called nucleons. Electrons orbit a positively charged nucleus. Mostly empty space between the orbits and the nucleus. Scattering experiments by Ernest Rutherford α-particles directed at thin gold foil. Observations of α-particles: Particle Proton Neutron Electron Most α-particles Observation Description Passed through the gold foil without deflection. Some α-particles Deflected at small angles. Approximately 1 in 8000 αparticles Deflected back towards the source at large angles. Proof of atomic model Atom is mostly empty space. Presence of a dense, positively charged nucleus which repels the α-particles Nucleus is very small and dense compared to the rest of the atom. Rutherford’s nuclear model Positive charge and most mass are concentrated in a small, dense nucleus. Electrons orbit the nucleus at a large distance away. Nucleus and electrons occupy about one-millionmillionth of the atom’s volume. Relative Mass 1 1 1 1840 Relative Charge +1 0 -1 Location In nucleus In nucleus Outside nucleus In a neutral atom the number of protons equals the number of electrons. Atomic number (Z ): Number of protons in the nucleus (it also equals the number of electrons). Mass number (A): Total number of nucleons (protons + neutrons) in the nucleus. Relationship: Number of neutrons = A − Z . Nuclide notation: Atom X is represented as A Z X , where A is the nucleon number and Z is the proton number. Relative charge: Product of proton number (Z ) and the charge of a proton. Relative mass: Total mass of neutrons and protons; approximately A times the mass of a proton. Isotopes The nucleus WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Forms of the same element with the same number of protons but different number of neutrons. 37 Example: Chlorine has isotopes 35 17 Cl and 17 Cl while 1 2 Hydrogen has isotopes 1 H , deuterium 1 H , and tritium 3H . 1 Reactors use controlled chain reactions to produce energy. Control rods absorb neutrons to regulate the reaction. Graphite moderates neutrons to slow down fission. Isotopes have identical chemical properties but different physical properties. Nuclides Radioactive isotopes are called radioisotopes or radionuclides and have unstable nuclei. Nuclear Energy Einstein’s equation: E = mc2 , where E is energy, m is mass, and c is the speed of light. Mass loss in nuclear reactions results in energy release. Nuclear reactions involve large energy changes compared to other physical and chemical changes. Nuclear fission Uranium-235 is an isotope that undergoes fission when struck by neutrons. Fission breaks the nucleus into smaller radioactive nuclei, releasing additional neutrons and energy. Mass loss is converted into kinetic energy of fission products. Neutrons from fission can trigger further fission reactions. Nuclear Reactor 5.2. Types of Radioactivity Natural Background Radiation Radiation sources include: Cosmic rays (high-energy particles from the Sun) are mostly absorbed by the atmosphere, but some reach the Earth's surface. Radon gas present in the air. Granite rocks in homes, particularly in Scotland, emit radioactive radon gas that can accumulate in poorly ventilated areas. Radioactive potassium-40 is present in food and absorbed by our bodies. Various radioisotopes are used in medical procedures. Radiation from nuclear power stations and fallout from nuclear bomb testing Ionising Effect of Radiation The ability of radiation to make atoms lose or gain electrons and become charged. A charged electroscope discharges when a lighted match or a radium source is brought near the cap. Electroscope Discharge: Neutral Atom → Positive Ion + Electron WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS A lighted match knocks electrons out of air molecules, creating positive ions. Radiation causes ionisation by neutralising the charge on the electroscope. Ionisation: Neutral Atom + Electron → Negative Ion Geiger–Müller (GM) Tube The ionising effect of radiation is used to detect radiation. Radiation entering a GM tube creates argon ions and electrons, which then cause more ionisation. Alpha, Beta, and Gamma Radiation Alpha Particles (α) The nucleus with two protons and two neutrons Stopped by thick paper; range in air is a few centimetres. The high ionising power of alpha particles is due to their increased mass (compared to gamma and beta), so it's more likely to ionise an atom Deflected by electric and magnetic fields. Represented as helium ions with a double positive charge. Beta Particles (β ) fast-moving electron Stopped by a few millimetres of aluminium; range in air is several metres. Lower ionising power than alpha particles. Deflected by electric and magnetic fields. Streams of high-energy electrons. Gamma Radiation (γ ) Electromagnetic radiation having high frequency Most penetrating Stopped only by many centimetres of lead. Least ionising power. Not deflected by electric and magnetic fields. Electromagnetic radiation. Type of Radiation Alpha (α) Mass Charge Penetrating Power High (Helium nucleus) +2 Beta (β) Low (electron) -1 Gamma (γ ) None (electromagnetic wave) 0 Low (stopped by paper) Moderate (stopped by few mm of aluminum) High (stopped by several cm of lead) Ionising Power High Moderate Low Particle Tracks Cloud chambers reveal the tracks of particles based on the ionisation they produce. Alpha Particles: Straight, thick tracks. Beta Particles: Thin, straight or twisted tracks. Gamma Rays: Eject electrons which then produce tracks similar to β particles. Electric deflection The positive alpha particles are heavier and slowly deflect towards the negative plate. The negative beta particles are lighter and quickly deflect towards the positive plate. The neutral electromagnetic gamma radiation remains undeflected. Magnetic deflection WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Alpha particles follow the rule of positive conventional current. Fleming’s left-hand rule is used with the middle finger pointing in the direction of alpha particles. Beta particles are shown in the direction opposite to the middle finger, as they represent electron flow, which is the opposite of conventional current. Gamma radiation is not deflected. In β-decay, a neutron changes into a proton and an electron. The proton remains in the nucleus, while the electron is emitted as a β-particle. The nucleon number stays the same, but the proton number increases by 1. Example: Radioactive carbon 14 6 C decays into nitrogen ( 14 N) by β-emission. 7 14 0 The equation for this decay is: 14 6 C →7 N +−1 e Gamma Emission (γ-emission) After α- or β-decay, some nuclei are left in an excited or energetic state. Rearrangement of protons and neutrons releases energy in the form of γ-emissions. γ-emissions are high-energy electromagnetic waves with no mass or charge. Nuclear Stability 5.3. Radioactive decay and half-life Radioactive Decay Radioactive decay is the emission of an α-particle or a βparticle from an unstable nucleus. This changes the nucleus into that of a different element until a stable element is formed. These changes are spontaneous and random Alpha Decay (α-decay) An α-particle is a helium nucleus with two protons and two neutrons. When an atom undergoes α-decay, its nucleon number decreases by 4 and its proton number decreases by 2. Example: When radium (226 88 Ra) emits and alpha particle, 222 it becomes radon (86 Rn). 222 4 The equation for this decay is: 226 88 Ra →86 Rn +2 He Stability of a nucleus depends on the number of protons (Z ) and neutrons (N ). Stable nuclides fall within a specific stability level called the stability line. For light nuclides, N = Z . For heavier nuclides, N > Z . Unstable nuclides decay to move towards the stability line. Nuclides above the stability line decay by β-emission to decrease the N Z ratio. Nuclides below the stability line decay by beta emission (β+) to increase the N Z ratio. Nuclei with more than 82 protons usually decay by αemission. Half-Life Beta Decay (β-decay) WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS The half-life of an isotope is the time taken for half the nuclei in a sample to decay. It is a measure of the rate at which a radioactive substance decays. Each isotope has its own special half-life. It can be from fractions of a second to millions of years. A decay curve plots the activity of a sample over time, showing the exponential decrease in activity. The activity decreases by half in each half-life period from the previous half-life period. Example: If a sample's activity is 80 decays per second, it will reduce to 40 in one half-life, then to 20 in the next, and so on. Radioactive decay is random and unpredictable; the exact time when a particular nucleus will decay cannot be determined. The overall decay rate of a sample follows a predictable pattern, called its half-life. Exposure to small doses of radiation is not damaging, but large doses are harmful to health. Nuclear radiation's ionising effect damages cells and tissues, it can lead to gene mutations. Damage can cause cell death and cancers. α-particles are less dangerous unless the source is ingested or inhaled. β- and γ-radiation can cause radiation burns, eye cataracts, and cancer. Radiation hazard signs warn of the presence of radioactive material. Safety Precautions 5.4. Safety precautions Dangers of Nuclear Radiation Minimize exposure time to radiation. Keep a large distance between the radiation source and individuals. Use shielding materials that absorb radiation to protect people. In industry, sources are handled with long tongs and transported in thick lead containers. Workers are protected by lead and concrete walls and wear radiation dose badges. Radiation dose badges track the amount of radiation exposure over a period, typically one month. The badge has windows that allow different types of radiation to expose photographic film, indicating exposure levels when developed. 6. Space Physics 6.1. The Earth and the solar system WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Motion of the Earth The Earth spins on its axis, causing day and night. One complete rotation takes 24 hours. Day is for the half of the Earth facing the Sun and night for the half facing away. Waning (where the moon's illumination decreases) phases follow, leading to the last quarter and old crescent Rising and setting of the Sun Earth's rotation causes the Sun to appear to move east to west daily. Rises exactly in the east and sets exactly in the west at equinoxes. In northern hemisphere summer, rises north of east and sets north of west. In winter, rises and sets south of these points. The seasons Caused by Earth's motion around the Sun (365 days) and tilt of its axis. Motion of the Moon Moon is a satellite of Earth, orbiting approximately every month Average distance from Earth is about 400,000 km. Revolves on its axis, always showing the same side to Earth Reflects sunlight, has no atmosphere, weaker gravitational field (one-sixth of Earth) Phases of the Moon Moon's appearance changes during its monthly orbit New Moon: Moon between Sun and Earth, unlit side faces Earth Crescent appears and increases until the first quarter (half of the Moon visible) Full Moon: Moon opposite Earth from the Sun, fully visible WWW.ZNOTES.ORG Orbital speed Average orbital speed: u = 2πr T r is the average radius of the orbit. T is the orbital period (time for one orbit) The Moon travels in a circular path around the Earth Distance traveled in one orbit is the circumference of the circle, 2πr Time taken for one orbit is T Speed is distance divided by time, so orbital speed is 2πr T The Solar System It contains: The sun as a star Eight planets in elliptical orbits (slightly oval orbits) Dwarf planets and asteroids orbiting the Sun Moons orbiting many planets Smaller bodies like comets and natural satellites Inner Planets Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Mercury, Venus, Earth, Mars Small, similar size Solid and rocky with layered structures High density Formed close to the Sun where it was too hot for gases to condense, allowing only metals and silicates to form solid bodies In the early Solar System, the Sun's heat caused lighter gases to evaporate, leaving only heavy elements like iron and silicon to form solid planets. Dust embedded in ice made from water and methane Orbits the Sun in highly elliptical paths Develop a bright long tail when approaching the Sun due to radiation pressure Outer Planets Jupiter, Saturn, Uranus, Neptune Much larger and colder Mainly consist of gases, low density Many moons and rings of icy materials Formed in cooler regions where gases could condense, capturing even the lightest elements In the outer regions of the Solar System, lower temperatures allowed gases like hydrogen and helium to remain in solid or liquid forms, leading to the formation of gas giants with thick atmospheres. Elliptical Orbits Planets, dwarf planets, and comets orbit the Sun in an ellipse Sun is at one focus of the ellipse, not the center Comets have highly elliptical orbits, while planets' orbits are more circular Origin of the Solar System Asteroids Pieces of rock of various sizes, mostly between Mars and Jupiter Orbit around the Sun Similar density to inner planets Burn up in Earth's atmosphere as meteors Formed from gravitational attraction pulling together clouds of hydrogen gas and dust (nebulae) Solar System formed about 4500 million years ago Planets formed from the disc of matter left over from the nebula that formed the Sun Inner planets formed from materials with high melting temperatures like metals and silicates Outer planets formed from light molecules that existed in solid icy forms, growing large enough to capture hydrogen Comets Travel Times WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Distance from the Sun to Earth: approximately 150 million km (1.5 × 108 km) Speed of light: 300,000 kilometers per second (km/s) Using the formula for time: Time = Distance Speed Substitute the values: 8 Time = 1.5×10 300,000 Calculate the time: 8 seconds ≈ 500 seconds Time ≈ 1.5×10 300,000 Convert the time from seconds to minutes: Time ≈ 500 60 ≈ 8.33 minutes Hot and dense enough for hydrogen to fuse into helium. Fusion process releases energy, maintaining high core temperatures. Some core energy moves to outer layers, which emit electromagnetic radiation. Light-years Distance light travels in a vacuum in one year. 1 light-year = 9.5 × 10¹² km = 9.5 × 10¹⁵ m Galaxies Large collections of stars, gas, and dust. It takes light from the sun around 8 minutes to reach the Earth. 6.2. The sun Medium-sized star composed mainly of hydrogen and helium. Emits energy in the infrared, visible, and ultraviolet regions of the electromagnetic spectrum. Source of Energy Energy from nuclear reactions in the core. Hydrogen undergoes nuclear fusion to form helium, releasing energy. Energy from the core heats outer layers, causing them to glow and emit radiation. 6.3. Origin and life cycle of stars Formation Interstellar clouds of dust and gas collapse under gravitational attraction. A protostar forms as mass increases and core temperature rises. Hydrogen fuses into helium when the core is hot enough, resulting in a star. Star Types Large mass: Blue or white stars. Smaller mass: Yellow or red dwarfs (e.g., the Sun). Life Cycle of Stars Stable Phase Forces of gravity inward balance with thermal pressure outward. Stable phase lasts up to 10 billion years. Hydrogen converts to helium in the core. Red Giant/Red Supergiant As hydrogen depletes, the star becomes unstable. Core collapses; outer layers expand and cool. Star turns into a red giant (or red supergiant if massive). Helium fuses into carbon in the core. Low Mass Stars Nuclear Reactions in Stars Stars like the Sun are powered by nuclear fusion. Core conditions End Stage Core collapses into a white dwarf after all helium is used. Outer layers expelled, forming a planetary nebula. White dwarf cools into a black dwarf over about a billion years. High Mass Stars (more than 8 times the Sun’s mass) WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS End Stage Use hydrogen rapidly, with a shorter stable phase (about 100 million years). After helium fusion, core collapses into a red supergiant. Fusion of carbon into heavier elements occurs until iron forms. Supernova explosion releases energy and heavy elements into space. Neutron Star: Dense core, may act as a pulsar. Black Hole: Extremely dense core with gravitational field so strong that even light cannot escape; identified by X-ray radiation from nearby material. Occurs when a source of waves (e.g., sound or light) moves relative to an observer. Approaching Source: Waves are compressed, resulting in a higher frequency and pitch (blue shift for light). Receding Source: Waves are stretched, resulting in a lower frequency and pitch (red shift for light). Speed of Recession 6.4. The universe Milky Way Approximately 100,000 light-years in diameter. Contains around 800 billion or more stars. A spiral galaxy with a central bulge and spiral arms. Redshift The phenomenon where light from distant galaxies shifts towards the red end of the spectrum (longer wavelength). Light emitted from stars in distant galaxies appears redder compared to light from closer galaxies. Doppler Effect The speed at which distant galaxies are moving away can be calculated from the amount of redshift observed. Some of the most distant galaxies are receding at speeds up to one-third the speed of light. The observed redshift supports the idea that the Universe is expanding, which is consistent with the Big Bang theory. Big Bang Theory Initial State: Proposes that the Universe began from an extremely hot and dense state around 14 billion years ago. Expansion: The Universe has been expanding ever since the Big Bang. Microwave Background Radiation This radiation is a remnant from the Big Bang and fills the entire Universe. The radiation has been redshifted into the microwave region due to the expansion of the Universe. Provides strong evidence for the Big Bang theory and insights into the early Universe. Age of the Universe WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE PHYSICS Hubble’s Law: The relationship between the speed of recession (v ) and the distance (d) of galaxies is given by: v = H0 × d Hubble Constant (H0 ): H0 = vd H0 measures the rate of the Universe's expansion. A higher value indicates a faster rate of expansion. H0 is estimated to be approximately 2.2 × 10−18 s−1 Age Estimation: The age of the Universe is approximately: Age of the Universe ≈ H10 Detailed Calculation Age of the Universe ≈ 2.2×101−18 s−1 ≈ 4.5 × 1017 s 4.5×1017 s Age of the Universe ≈ 3.2×10 7 s/year ≈ 1.4 × 1010 years ≈ 14 billion years WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Maryam at Homeschooled on 07/02/25. CAIE IGCSE Physics © ZNotes Education Ltd. & ZNotes Foundation 2024. All rights reserved. This version was created by Maryam on Fri Feb 07 2025 for strictly personal use only. 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