Definitions and Concepts for CAIE Physics GCSE
Topic 1: General Physics
Definitions in ​bold ​are for extended students only
1.1 Length and Time
Analogue device​:​ A measuring device that requires the user to read from a scale
to obtain the measurement.
Digital device​:​ A measuring device that displays the measurement on a display,
rather than requiring the user to read from a scale.
Distance: ​A measure of how far an object moves. It doesn’t depend on direction
and is therefore a scalar quantity.
Micrometer screw gauge​:​ ​A measuring implement used to accurately
measure very small distances.
Pendulum​:​ A pendulum is a weight suspended from a pivot so that it can swing
freely.
Volume​:​ ​The amount of space that a substance or object occupies.
1.2 Motion
Acceleration​:​ ​The rate of change of velocity. It can be calculated from the
gradient of a velocity-time graph. ​Denoted by non-zero gradient in a speed-time
graph.
Air resistance​: The resistance of an object’s motion through air. It is a form
of friction due to the air particles colliding with the object.
Average speed​: ​The average speed is calculated by dividing the distance
travelled by the time taken.
Deceleration​: Negative acceleration.
Distance–time graph​: ​A plot of how an object’s distance changes over time. ​The
gradient of the graph at any point, equals the object’s speed at that point.
Free fall​: ​Motion under the force of gravity alone.
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Linear motion:​ Motion for which the acceleration is not constant.
Speed​: ​A scalar quantity that is a measure of the rate of change of distance.
Speed–time graph​: ​A plot of how an object’s speed changes over time. ​The
gradient of the graph at any point, equals the object’s acceleration at that
point​. The area under the graph represents the distance travelled.
Terminal velocity​: Steady speed achieved by an object freely falling through
a gas or liquid.
Gravitational field​: A region where a mass will experience a non-contact
gravitational force. All matter produces a gravitational field around it, and
the greater its mass, the stronger the field.
Velocity​: A vector quantity that is a measure of the rate of change of
displacement. It is the speed in a given direction.
1.3 Mass and Weight
Balance​: ​A piece of apparatus that can compare different weights to demonstrate
which is greater. It can also be used to compare masses.
Mass​: ​Mass is a measurement of how much matter is in an object. ​It is also the
resistance that a body offers to a change in its speed or position upon the
application of a force.
Weight​: ​The force acting on an object due to gravity.​ It is equal to the product of
the object’s mass and the gravitational field strength at its location.
1.4 Density
Density​: ​The mass per unit volume of an object.
Displacement​: ​It is the object's overall change in position.​ ​Calculated by the
difference between final and initial readings.
1.5 Forces
1.5.1 Effects of Forces
Air resistance:​ ​The resistance of an object’s motion through air. It is a form of
friction due to the air particles colliding with the object.
Extension–load graphs​: ​A graph that shows how the extension of an object
varies with the load applied. For a spring, this should initially form a straight line
that passes through the origin.
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Friction​: ​A resistive contact force that acts to oppose the relative motion between
two surfaces. Some energy of the object in contact is lost as heat in the process.
Hooke’s law ​: The extension of a spring is directly proportional to the force
applied to it, up to the limit of proportionality. The constant in this
relationship is known as the spring constant.
Limit of proportionality​: The point beyond which the extension of an elastic
object is no longer directly proportional to the force applied to it.
Resultant force​: ​The single force that can replace all the individual forces acting
on an object, and have the same effect.
Spring constant:​ A measure of a spring’s stiffness. The higher the spring
constant, the smaller the extension is for a given force.
1.5.2 Turning Effect
Moment of a force​: ​The turning effect of a force, equal to the product of the
magnitude of the force and the perpendicular distance from the pivot to the line of
action of the force.
Principle of moments​:​ For an object in equilibrium, the sum of the clockwise
moments about any point on the object must equal the anticlockwise moments
about that same point.
1.5.3 Conditions for Equilibrium
Equilibrium​: ​An object in equilibrium has a zero resultant force and a zero
resultant moment.
Resultant force​: ​The single force that can replace all the individual forces acting
on an object, and have the same effect.
Turning effect​:​ It is also known as the moment of the force.
1.5.4 Centre of Mass
Centre of mass​: ​The single point through which all the mass of an object can be
said to act.
Plane lamina​:​ A body whose mass is concentrated in a single plane.
Stability​: ​A measure of the likelihood of an object toppling. An object is unstable if
the object’s line of action of weight lies outside of its base.
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1.5.5 Scalars and Vectors
Resultant vector​: ​It is​ ​the sum of two or more vectors which has its own
magnitude and direction
Scalars​:​ ​Quantities that only have a magnitude, not a direction.
Vectors​:​ ​Quantities that have both a magnitude and direction. They are
represented by an arrow, with the length representing the magnitude and the
arrowhead representing the direction.
1.6 Momentum
Conservation of momentum​:​ ​The total momentum of a system before an
event is always equal to the total momentum of the system after the event.
Impulse​: The change of a system’s momentum as a result of a force acting
over a period of time
Momentum​: The product of an object’s mass and velocity.
1.7 Energy, Work and Power
1.7.1 Energy
Chemical energy: ​A store of energy found in things such as batteries, fuels and
food.
Elastic potential (strain) energy:​ The store of energy that stretched or
compressed objects contain.
Electrical current​: ​An electric current is a flow of electric charge in a circuit.
Gravitational potential energy​: ​The store of energy that all raised matter has. ​It
is directly proportional to the mass of the object, the distance that it is
raised, and the gravitational field strength at that point.
Internal energy​: ​It is defined as the energy associated with the random,
disordered motion of molecules.
Kinetic energy: ​The store of energy that all moving matter has. ​It is directly
proportional to the object’s mass and to the square of its velocity.
Nuclear energy​: ​Non-renewable energy that is generated from the energy stored
in the nuclei of radioactive isotopes. It is released in processes known as nuclear
fission and nuclear fusion.
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Principle of conservation of energy​: ​The law that energy can be transferred,
stored or dissipated but never created or destroyed.
1.7.2 Energy Resources
Chemical energy​: ​A store of energy found in things such as batteries, fuels and
food.
Efficiency​: ​The ratio of useful output energy transfer to total energy input. It can
never exceed 1 (or 100%), due to the conservation of energy.
Geothermal energy​: ​Renewable energy generated from the conversion of the
thermal energy found below the Earth’s surface into electrical energy.
Hydroelectric power:​ Renewable energy generated by water stored at a height,
and released through a turbine. The turbine turns a generator which converts the
kinetic energy into electrical energy.
Nuclear fission​: ​It ​is a process where the nucleus of an atom is split into two or
more smaller nuclei.
Nuclear fusion​: It ​is the process of making a single heavy nucleus (part of an
atom) from two lighter nuclei​.
Renewable energy resource: ​An energy resource that can be replenished whilst
it is being used.
Solar energy​: ​Renewable energy generated by converting the energy of the sun
into electrical energy, usually by using a solar panel.
Tidal energy​: ​Renewable energy generated by trapping water when at high tide,
and then releasing it through a turbine. The turbine turns a generator which
converts the kinetic energy into electrical energy.
Wind energy​: ​Refers to the process of creating electricity using the wind.
1.7.3 Work
Work done​: ​Work is done on an object when a force causes it to move through a
distance. It is equal to the product of the distance travelled and the magnitude of
the force in the direction of motion.
1.7.4 Power
Power​: ​The rate at which energy is transferred, or the rate at which work is done.
It is calculated by dividing the work done by the time taken.
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Work done​: ​Work is done on an object when a force causes it to move through a
distance. It is equal to the product of the distance travelled and the magnitude of
the force in the direction of motion.
1.8 Pressure
Atmosphere: ​The thin layer of air surrounding the Earth, which gets less dense
with increasing altitude. The pressure also decreases with increasing altitude.
Atmospheric pressure​: ​It is the force exerted on a surface by the air above it as
gravity pulls it to Earth
Manometer​: ​A U-shaped tube of liquid that allows the pressure on a column of
liquid to be measured.
Mercury barometer​: ​A measuring device that measures changes in atmospheric
pressure.
Pressure​: ​The force acting perpendicular to a surface, per unit area.
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CIE Physics IGCSE
Topic 1: General Physics
Summary Notes
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Length and time
●
●
●
●
●
A ruler (rule) is used to measure the length of an object between 1mm and 1m.
The volume of an object of irregular shape can be measured by placing it into a measuring
cylinder full of water. This causes the water level to rise, and this rise is equal to the volume
of the object.
A micrometer screw gauge is used to measure very small distances that a rule
cannot measure.
Analogue and digital clocks and devices are used to measure time intervals.
An average value for a small distance and for a short time interval can be found by
measuring multiples (including the period of a pendulum).
Motion
●
Speed is defined as the distance traveled per unit time. If the speed of something is
changing, it is accelerating. The acceleration of free fall near to the Earth is constant.
●
𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑠𝑝𝑒𝑒𝑑 =
●
Distance is measured in mm, cm, m or km and time measured in ms, s, minutes or hours.
Remember to convert units to make sure everything is equivalent! For example if distance
𝑡𝑜𝑡𝑎𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝑡𝑜𝑡𝑎𝑙 𝑡𝑖𝑚𝑒
𝑣=
𝑑
𝑡
is in 𝑘𝑚 and time is in ℎ𝑜𝑢𝑟𝑠, then calculate
𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
1000
and 𝑡𝑖𝑚𝑒 × (60 × 60)to get everything
●
in metres and seconds.
Velocity is the speed in a given direction.
●
Acceleration is the rate of change of velocity: 𝒂𝒄𝒄𝒆𝒍𝒆𝒓𝒂𝒕𝒊𝒐𝒏 =
𝒗−𝒖
𝒕
𝒄𝒉𝒂𝒏𝒈𝒆 𝒊𝒏 𝒗𝒆𝒍𝒐𝒄𝒊𝒕𝒚
𝒕𝒊𝒎𝒆
𝒂=
In a distance-time graph:
●
●
●
●
The gradient is velocity
○ Negative gradient is returning back to the
starting point
A horizontal line means it is stationary
If the distance is zero, it is back at the starting point
A curved line means that the velocity is changing
and it is accelerating.
In a speed-time graph:
●
●
●
●
●
The gradient is acceleration
○ Negative gradient (i.e. negative
acceleration) is deceleration
If the speed is zero, it is at rest
A horizontal line means constant speed
The area under the line is the distance travelled
A curved line means that the acceleration is
changing.
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Mass and weight
Mass:
● Mass is a measure of how much matter is in an object.
● It is a property that resists change in motion.
Weight:
● Weight is a gravitational force (the effect of a gravitational field on a mass) measured in
Newtons: 𝑤𝑒𝑖𝑔ℎ𝑡 = 𝑚𝑎𝑠𝑠 × 𝑔𝑟𝑎𝑣𝑖𝑡𝑎𝑡𝑖𝑜𝑛𝑎𝑙 𝑓𝑖𝑒𝑙𝑑 𝑠𝑡𝑟𝑒𝑛𝑔𝑡ℎ = 𝑚𝑔
● The gravitational field strength on Earth is 10Nkg -1.
● Weights (and hence masses) can be compared using a balance.
Same object on two different planets:
● The mass is the same
● The gravitational field strength g on the two planets will be different (i.e. not 10 for both) so
the weight is different.
Acceleration in free fall is due to gravity, and is the same as g, i.e. 10𝑚𝑠 −2
Density
𝑚𝑎𝑠𝑠
𝑚
𝑉
●
The density is defined as the mass per unit volume: 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 = 𝑣𝑜𝑙𝑢𝑚𝑒
●
The density ρ is in kilograms per metre cubed, kg/m 3, the mass m is in kilograms, kg, and
the volume V is in metres cubed, m 3.
𝜌=
To find the density of a liquid:
●
Find the mass of the measuring cylinder by placing it on a balance, then fill it with the liquid
and measure the new mass. The difference in masses is the mass of the liquid.
●
The volume can be read from the cylinder and the density calculated using the equation.
To find the density of solid:
● Measure the mass of the solid by placing it on a balance.
● If the solid is regularly shaped, measure its dimensions using a ruler or other measuring
tool and then use a mathematical formula to find the volume.
● If the solid is irregularly shaped, immerse it in water and measure the volume of the water
displaced. This is the volume of the solid.
● Find the density using the equation.
The density of water is 1g/cm 3; if the density of an object is greater than this it will sink in water - if
less, it will float.
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Forces
Effects of forces
●
●
●
Newton’s first law states that an object has a constant velocity unless acted on by a
resultant force.
Newton’s second law states that 𝒇𝒐𝒓𝒄𝒆 = 𝒎𝒂𝒔𝒔 × 𝒂𝒄𝒄𝒆𝒍𝒆𝒓𝒂𝒕𝒊𝒐𝒏 𝑭 = 𝒎𝒂
Newton’s third law states that every action force has an equal and opposite reaction force.
For example, the force of the Earth’s gravity on an object is equal and opposite to the force
of the object’s gravity on the Earth.
For example, motion of a body falling in a uniform gravitational field:
● Initially, there is no air resistance and the only force acting on it is weight
● As it falls, it accelerates which increases its speed and hence air resistance
● This causes the resultant force downwards to decrease
● Therefore the acceleration decreases, so it is not speeding up as quickly
● Eventually they are equal and opposite and balance so there is no resultant force
● So there is no acceleration and the terminal velocity is reached
Friction is a force between two surfaces which impedes motion and results in heating. Air
resistance is a form of friction.
To find the resultant of two or more forces acting along the same line, they should be added
together if in the same direction and subtracted if in the opposite direction.
For an object moving in a circle, with constant speed:
● The speed is constant, but the direction is always changing
● This means the velocity is always changing
● Therefore it is accelerating and there must be a force perpendicular to its velocity
towards the centre of the circle.
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A force may produce a change in size and shape of a body. This is called deformation:
●
●
Elastic deformation:
○ The object returns to its original shape when the load has been removed, an
example being a spring being stretched under normal usage.
Plastic deformation:
○ The object does not return to its original shape when the load has been removed,
an example being a spring that has been stretched too far.
Hooke’s law states that for a spring, 𝐹 = 𝑘𝑥 where F is the force applied to the spring in 𝑁, k
is the spring constant in 𝑁𝑚−1 , and x is the extension in 𝑚.
Linear (straight line) force-extension graph:
● Elastic deformation following Hooke’s law
○ The point it stops being linear is called
the limit of proportionality. From then
on, it does not obey Hooke’s law.
● Gradient is the spring constant, k
Non-linear (curved line) force-extension graph:
● Plastic deformation not following Hooke’s law
● After the plastic region, it will fracture
Turning effect
The moment of a force is a measure of its turning effect: 𝑚𝑜𝑚𝑒𝑛𝑡 𝑜𝑓 𝑎 𝑓𝑜𝑟𝑐𝑒 = 𝑓𝑜𝑟𝑐𝑒 ×
𝑝𝑒𝑟𝑝𝑒𝑛𝑑𝑖𝑐𝑢𝑙𝑎𝑟 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑚𝑜𝑚𝑒𝑛𝑡 = 𝐹𝑑
For example, when riding a bike, pressing your foot down on the pedal causes a moment about the
pivot, turning the pedal arms.
●
●
●
The pivot point is the point which the object can rotate about.
If a force is applied in the same line as the pivot (see first example in diagram) the object
will not rotate, and will remain stationary.
If the force applied is in a different line to the pivot, it will rotate in the direction of the force.
○ If it is perpendicular to the object, then the perpendicular distance is the length of
the object (see second example in diagram).
○ If it is not perpendicular to the object, then the perpendicular distance to the pivot
must be found (see third example in diagram).
Remains stationary
Conditions for equilibrium
Rotates clockwise
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An object is in equilibrium when the sum of clockwise moments equals the sum of anticlockwise
moments (the principle of moments) and there is no resultant force.
The principle of moments can be applied to check whether something balances. An experiment
can be performed to show that there is no net moment on a body in equilibrium by pivoting
a uniform ruler at its centre and placing different masses at different distances from the
centre on either side until it balances, and showing that the clockwise and anticlockwise
moments are equal.
Centre of Mass
The centre of mass of a body is the point at which all of its mass can be considered to act. To
calculate the centre of mass of a card:
1. Hang up the card and suspend a plumb line from the same place.
2. Mark the position of the thread.
3. Repeat the above steps with the card suspended from different places.
4. Where these lines intersect is the centre of mass.
If the centre of mass is below the point of suspension of an object, it will be in stable equilibrium
(e.g. a hanging plant pot). If the centre of mass is above the point of suspension of an object, it will
be in unstable equilibrium (e.g. a pencil placed on its sharp end). If the line of action of the object’s
weight moves outside the base, there will be a resultant moment and it will topple.
Scalars and vectors
●
●
A vector has a magnitude and a direction.
A scalar has just a magnitude.
Examples:
Scalars
Vectors
Distance
Displacement
Speed
Velocity
Time
Acceleration
●
Vectors can be represented by
arrows. To determine the resultant of
two vectors graphically, they must be
placed head to tail; the line between
the start and finish is the resultant.
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Momentum
Momentum is the product of mass and velocity: 𝒎𝒐𝒎𝒆𝒏𝒕𝒖𝒎 = 𝒎𝒂𝒔𝒔 ×
𝒗𝒆𝒍𝒐𝒄𝒊𝒕𝒚 𝒑 = 𝒎𝒗
● Impulse is the product of force and time, equal to the change in momentum:
𝒊𝒎𝒑𝒖𝒍𝒔𝒆 = 𝑭𝒕 = 𝒎𝒗 − 𝒎𝒖
In a collision, the total momentum before is equal to the total momentum afterwards, known
as the principle of the conservation of momentum.
●
In elastic collisions, the total kinetic energy before is equal to the total kinetic energy after.
Example:
●
A 10kg stationary gun is loaded with a 10g bullet. It is fired, with the bullet travelling
at 𝟏𝟎𝟎𝒎𝒔−𝟏 . What is the recoil speed of the gun?
𝒕𝒐𝒕𝒂𝒍 𝒎𝒐𝒎𝒆𝒏𝒕𝒖𝒎 𝒃𝒆𝒇𝒐𝒓𝒆 = 𝟎
𝒕𝒐𝒕𝒂𝒍 𝒎𝒐𝒎𝒆𝒏𝒕𝒖𝒎 𝒃𝒆𝒇𝒐𝒓𝒆 = 𝒕𝒐𝒕𝒂𝒍 𝒎𝒐𝒎𝒆𝒏𝒕𝒖𝒎 𝒂𝒇𝒕𝒆𝒓𝒘𝒂𝒓𝒅𝒔
𝟎 = 𝟎. 𝟎𝟏 × 𝟏𝟎𝟎 + 𝟏𝟎𝒗
𝒗 = −𝟎. 𝟏𝒎𝒔−𝟏
So the recoil speed is 𝟎. 𝟏𝒎𝒔−𝟏 (-0.1ms-1 is the velocity which is a vector, so we take the
magnitude of it as we are finding the speed).
Energy, work and power
Energy transfers
Energy can be transferred between different forms including kinetic, gravitational potential,
chemical, elastic potential, nuclear and internal energy as a result of an event or process.
𝟏
●
Kinetic energy: 𝑬𝒌 = 𝒎𝒗𝟐
●
Gravitational potential energy: 𝐸𝑝 = 𝑚𝑔ℎ
𝟐
Energy can be transferred in various ways including:
● Forces e.g. when gravity accelerates an object downwards and gives it kinetic energy.
● Electrical currents e.g. when a current passes through a lamp and it emits light and heat.
● Heating e.g. when a fire is used to heat up an object.
● Waves e.g. vibrations cause waves to travel through the air as sound.
Work is done when a force moves something through a distance. The work done is equal to the
energy transferred.
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●
Work done: 𝒘𝒐𝒓𝒌 𝒅𝒐𝒏𝒆 = 𝒇𝒐𝒓𝒄𝒆 × 𝒅𝒊𝒔𝒕𝒂𝒏𝒄𝒆 𝑾 = 𝑭𝒅
Power is the rate at which energy is transferred or the rate at which work is done. For example, a
lamp with a greater power will be brighter because it transfers more energy from electrical energy
to light and heat energy in a given time.
●
Power: 𝑝𝑜𝑤𝑒𝑟 =
𝑒𝑛𝑒𝑟𝑔𝑦 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟𝑟𝑒𝑑
𝑡𝑖𝑚𝑒
𝑃=
𝐸
𝑡
Energy is always conserved. The total energy before is equal to the total energy after.
For example, when a ball is dropped, gravitational potential energy becomes kinetic energy
as it accelerates downwards. Upon impact with the floor, this kinetic energy will become
thermal energy and sound energy.
In any event or process energy tends to become more spread out among the objects and
surroundings (dissipated).
●
The efficiency is the ratio of the useful work done to the total energy supplied, often
expressed as a percentage.
𝒖𝒔𝒆𝒇𝒖𝒍 𝒆𝒏𝒆𝒓𝒈𝒚 𝒐𝒖𝒕𝒑𝒖𝒕
𝒖𝒔𝒆𝒇𝒖𝒍 𝒑𝒐𝒘𝒆𝒓 𝒐𝒖𝒕𝒑𝒖𝒕
○ Efficiency: 𝒆𝒇𝒇𝒊𝒄𝒊𝒆𝒏𝒄𝒚 = 𝒕𝒐𝒕𝒂𝒍 𝒆𝒏𝒆𝒓𝒈𝒚 𝒊𝒏𝒑𝒖𝒕 = 𝒕𝒐𝒕𝒂𝒍 𝒑𝒐𝒘𝒆𝒓 𝒊𝒏𝒑𝒖𝒕
●
The efficiency of a system can be increased by:
○ Reducing waste output (lubrication, thermal insulation, etc.)
○ Recycling waste output (e.g. absorbing thermal waste and recycling it as input
energy)
Energy sources
It is important to note that apart from geothermal, nuclear and tidal, the sun is the original
source of all energy on earth, released by nuclear fusion.
●
Renewable energy is energy which can be replenished as quickly as it is used. Examples
include:
○ Biofuel
○ Wind
○ Hydro-electricity
○ Geothermal
○ Tidal
○ Solar
○ Water waves
It is often more costly and less reliable than non-renewable energy (e.g. the wind is
intermittent and solar energy relies on good weather).
●
Non-renewable energy is used more for large-scale energy supplies due to the large
energy output per kilogram of fuel. Examples include:
○ Fossil fuels (coal, oil, gas)
○ Nuclear fuel
It is usually cheaper than renewable energy but is becoming less popular because one day
it will run out and it is harmful for the environment (e.g. burning fossil fuels releases
greenhouse gases which cause global warming).
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Pressure
Pressure in fluids causes a net force at right angles to any surface and is measured in Pascals.
𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 =
𝑓𝑜𝑟𝑐𝑒
𝑎𝑟𝑒𝑎
𝑝=
𝐹
𝐴
For example, lying down on a bed of nails compared to a single nail:
● The force applied is the weight of your body
● The total area is either a single pin point or many points spread out over a larger area
○ So on a bed of nails, the pressure is lower as the area is greater.
Measuring pressure:
● A barometer consists of a tube filled with mercury with a vacuum at
the top. Atmospheric pressure pushes down at the sides causing
the mercury to rise. The height of the mercury is measured to find
atmospheric pressure, where 760 mm or 29.92 in of mercury
corresponds to 1 atm.
● A manometer consists of a U-tube filled with mercury and with a
gas at either end. The difference in the height of the mercury on
either side can be measured to find the pressure difference
between the two ends of the tube.
The pressure beneath a liquid surface increases with depth and density.
● It is given by 𝒑 = 𝝆𝒈𝒉
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Definitions and Concepts for CAIE Physics GCSE
Topic 2: Thermal Physics
Definitions in ​bold ​are for extended students only
2.1 Simple Kinetic Molecular Model of Matter
2.1.1 States of Matter
Gases: ​A state of matter in which the particles are spread apart and have
high kinetic energies. Any intermolecular forces acting between the particles
are very weak.
Liquids: ​A state of matter in which the particles are in contact, but can flow
over each other. Intermolecular forces act between the particles.
Solids: ​A state of matter in which the particles are tightly packed together
and can only vibrate about their fixed positions. Strong intermolecular
forces act between the particles.
2.1.2 Molecular Model
Brownian motion: ​It ​is the random motion of particles suspended in a medium
Gas temperature​: ​The temperature of a gas is directly proportional to the average
kinetic energy of its molecules.
Kinetic molecular model of matter​: States that matter is made up of particles
that are constantly moving.
Pressure of a gas​: ​The perpendicular force(rate of change of momentum) per
unit area acting on the surfaces of a container as a result of the gas particles
colliding with it.
Suspension:​ ​A state in which particles are dispersed throughout a fluid.
2.1.3 Evaporation
Evaporation: ​It​ ​is the process of changing from a liquid or solid state into vapor
due to the escape of more-energetic molecules from the surface of a liquid. ​It is
influenced by temperature, surface area and draught over a surface.
Evaporative cooling: ​It is cooling due to evaporation ​due to the escape of
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more-energetic molecules from the surface of a liquid. ​As a result, a body in
contact with an evaporating liquid also experiences a loss in temperature.
2.1.4 Pressure Changes
Molecule:​ It is a particle made up of two or more atoms that are chemically
bonded together.
Temperature​: A measure of the average kinetic energy of the particles in a
substance. An increase in temperature will result in an increase in the particles’
kinetic energies and velocities.
Volume of a gas​: It is the quantity of three-dimensional space occupied by a gas.
2.2 Thermal Properties and Temperature
2.2.1 Thermal Expansion of Solids, Liquids and Gases
Application​: ​The action of putting something into operation.
Magnitude​: ​A numerical quantity or value.
Thermal expansion​: Thermal expansion is the increase, or decrease, of the size
(length, area, or volume) of a body due to a change in temperature.
2.2.2 Measurement of Temperature
Fixed points​: ​A well-defined reproducible temperature which can be used as a
reference point.
Liquid-in-glass thermometer​: A​n instrument for measuring and indicating
temperature​ in which the thermally sensitive element is a liquid contained in a
graduated glass envelope, which uses the thermal expansion of the liquid to
measure readings.
Linearity of a thermometer​: ​It is the property in a thermometer defined as the
same distance between all degree intervals.
Measurement​: It is ​the process of associating numbers with physical quantities.
Physical property​: ​is any property that is measurable, whose value describes a
state of a physical system.
Range of a thermometer​: ​It is the difference between the maximum and
minimum temperatures that the thermometer can read.
Sensitivity of a thermometer​:​ It is defined as the increase in the length of the
mercury column per unit increase in temperature.
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Thermocouple​: ​A device for measuring temperature in which a pair of wires
of dissimilar metals (such as copper and iron) are joined and the free ends
of the wires are connected to an instrument (such as a voltmeter) that
measures the difference in potential created at the junction of the two
metals.
2.2.3 Thermal Capacity (Heat Capacity)
Change in Thermal Energy: ​The product of the mass, specific heat capacity
and temperature change of a substance.
Internal energy​: The energy stored by the atoms and molecules that make up a
system. It is equal to the sum of the total kinetic and potential energies of the
particles in the system.
Specific heat capacity​: ​The amount of energy needed to increase the
temperature of one kilogram of a given substance by one degree Celsius.
Thermal capacity​: It is defined as the amount of heat to be supplied to a given
mass of a material to produce a unit change in its temperature.
2.2.4 Melting and Boiling
Boiling​: It is the physical process that results in the transition of a substance from
a liquid to a gas state without change in temperature.
Boiling point​: ​It is the temperature at which a substance changes state from a
liquid to a gas.
Condensation​:​ The changing from vapour state to a liquid state, when a
substance is cooled. As the molecules lose heat, they lose energy and slow down.
Evaporation​: ​Is the process by which an element or compound transitions
from its liquid state to its gaseous state below the temperature at which it
boils.
Latent heat​: The energy required for a substance to change state.
Melting​: It is the physical process that results in the transition of a substance from
a solid to a liquid state without change in temperature.
Melting point​: ​It is the temperature at which a substance changes state from solid
to liquid.
Solidification​: It ​is a phase transition in which a liquid turns into a solid when its
temperature is lowered to or below its freezing point. ​As the molecules lose heat,
they lose their kinetic energy and band together.
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Specific ​latent heat of vaporisation: ​The amount of energy needed to change
the state of one kilogram of a substance from liquid state to vapour state,
whilst held at constant temperature.
Specific ​latent heat of fusion: ​The amount of energy needed to change the
state of one kilogram of a substance from solid state to liquid state, whilst
held at constant temperature.
Specific latent heat​: The amount of energy needed to change the state of
one kilogram of a substance, whilst held at constant temperature.
2.3 Thermal Processes
2.3.1 Conduction
Conduction: ​The transfer of heat energy through the vibrations of particles in a
medium.
Electron​: ​A stable subatomic particle with a charge of negative electricity,
found in all atoms
Lattice Vibration: ​is the oscillations of atoms in a solid about the equilibrium
position
Thermal conductor​: It is a material that allows energy in the form of heat, to be
transferred within the material, without any movement of the material itself.
2.3.2 Convection
Convection​: The transfer of heat energy through convection currents in a fluid.
Density​: It is a property of the substance, also known as mass per unit volume.
2.3.3 Radiation
Absorption: ​The transfer of the energy of a wave to matter as the wave passes
through it.
Electromagnetic spectrum: ​A group of transverse waves that cover a large
range of frequencies and wavelengths. The highest frequency waves in the
spectrum are gamma-rays and the lowest are radio waves.
Infrared radiation: ​A type of radiation that all objects emit and absorb. ​The hotter
an object is, the greater the infrared radiation it emits in a given time.
Medium: ​Is defined as the substance that transfers energy from one substance to
another substance.
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Reflection​: The bouncing back of a wave at a boundary.
Thermal energy: ​The store of energy that all objects with a temperature contain.
The higher the temperature, the greater its thermal energy store.
2.3.4 Consequences of Energy Transfer
Conduction: ​The transfer of heat energy through the vibrations of particles in a
medium.
Convection​: The transfer of heat energy through convection currents in a fluid.
Radiation: ​The emission of energy as electromagnetic waves or as moving
subatomic particles.
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CIE Physics IGCSE
Topic 2: Thermal Physics
Summary Notes
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Simple kinetic molecular model of matter
Molecular model
●
Solids
○
○
○
○
Molecules close together in regular pattern
Strong intermolecular forces of attraction
Molecules vibrate but can’t move about
Cannot flow, have fixed shape and cannot be
compressed
●
Liquids
○ Molecules close together in random arrangement
○ Weaker intermolecular forces of attraction than solids
○ Molecules move around each other
○ Flow, take the shape of their container and cannot be
compressed
●
Gases
○
○
○
○
Molecules far apart in random arrangement
Negligible/very weak intermolecular forces
Molecules move quickly in all directions
Flow, completely fill their container and can be
compressed
Temperature, pressure and volume
Brownian motion:
● Gas molecules move rapidly and randomly
● This is due to collisions with other gas molecules
● Massive particles may be moved by light, fast-moving molecules
The temperature of a gas is related to the average kinetic energy of the molecules. The higher the
temperature, the greater the average kinetic energy and so the faster the average speed of the
molecules.
Gases exert pressure on a container due to collisions between gas molecules and the wall. When
the molecules rebound off the walls, they change direction so their velocity and therefore
momentum changes. This means they exert a force because force is equal to the change in
momentum over time.
●
●
At a constant volume, if the temperature increases, the pressure increases because the
molecules move faster so they collide harder and more frequently with the walls.
At a constant temperature, if the volume increases, the pressure decreases because the
molecules collide less frequently with the walls.
○ For a gas at fixed mass and temperature, 𝒑𝑽 = 𝒄𝒐𝒏𝒔𝒕𝒂𝒏𝒕, where p is the
pressure in Pascals and V is the volume in m 3.
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Evaporation
●
●
●
Evaporation is the escape of molecules with higher energy from the surfaces of liquids.
After they escape, the remaining molecules have a lower average kinetic energy which
means the temperature is lower (i.e. evaporation cools the liquid).
To increase the rate of evaporation:
o Increase temperature: more higher energy molecules
o Increase surface area: more molecules at the surface
o Draught: molecules are removed before returning to the liquid
Evaporation cools a body in contact with an evaporating liquid (i.e. skin with sweat on it) because
the liquid absorbs energy from the body so that it can continue to evaporate.
Thermal properties and temperature
Thermal expansion
When something is heated, it expands because the molecules take up more space:
● When a solid is heated, the molecules vibrate more but stay in place, so the relative
order of magnitude of the expansion is small.
● When a liquid is heated, it expands for the same reason as a solid, but the
intermolecular forces are less so it expands more.
● When a gas is heated, the molecules move faster and further apart, so the relative
order of magnitude of the expansion is the greatest.
Some applications and consequences of thermal expansion include:
● Railway tracks having small gaps so that they don’t buckle when they expand
● The liquid in a thermometer expands with temperature and rises up the glass
Thermal capacity
When the temperature of a body rises, its internal energy increases and its molecules vibrate
more.
● The specific heat capacity is the amount of energy required to raise the temperature
of 1kg of a substance by 1℃.
○ 𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑡ℎ𝑒𝑟𝑚𝑎𝑙 𝑒𝑛𝑒𝑟𝑔𝑦 = 𝑚𝑎𝑠𝑠 × 𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑐 ℎ𝑒𝑎𝑡 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦 ×
𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑐ℎ𝑎𝑛𝑔𝑒 ∆𝐸 = 𝑚𝑐∆𝑇where ΔE is the change in thermal energy in
J, c is the specific heat capacity in Jkg-1℃-1, m is the mass in kg and ΔT is the
change in temperature in ℃.
● The thermal capacity of a body is how much energy needs to be put in to raise its
temperature by a given amount.
○ The thermal capacity of a system is given by: 𝒕𝒉𝒆𝒓𝒎𝒂𝒍 𝒄𝒂𝒑𝒂𝒄𝒊𝒕𝒚 = 𝒎𝒄
Melting and boiling
Melting and boiling occur when energy is put in to a body without a change in temperature.
● The melting point is the temperature at which a given solid will melt when heated.
● The boiling point is the temperature at which a given liquid will turn into a gas when heated.
● Condensation is when some molecules in a gas do not have enough energy to remain as
separate molecules, so they come close together and form bonds, becoming liquid.
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●
Freezing is when the molecules in a liquid slow down enough that their attractions cause
them to arrange themselves into fixed positions, becoming solid.
Evaporation is different to boiling because it can happen at any temperature and only
occurs at the surface of the liquid.
●
●
The specific latent heat is the amount of energy needed to change the state of 1kg of
a substance.
○ Specific latent heat of fusion is the energy to melt/freeze
○ Specific latent heat of vaporization is energy to boil/condense
𝑒𝑛𝑒𝑟𝑔𝑦 = 𝑚𝑎𝑠𝑠 × 𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑙𝑎𝑡𝑒𝑛𝑡 ℎ𝑒𝑎𝑡
𝐸 = 𝑚𝑙where E is the energy needed in J, m
is the mass in kg, and l is the specific latent heat in Jkg -1.
When a body changes state, energy goes towards making the molecules more free from each
other rather than increasing their kinetic energy.
Graph showing the temperature of ice with time when
energy is put in at a constant rate:
● From A to B the ice is rising in temperature
● From B to C it is melting into water
● From C to D the water is rising in temperature
● From D to E the water is boiling into steam
● From E to F the steam is rising in temperature
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Measuring Temperature
Thermocouple:
● Contains two different metals which meet
● The temperature difference between them causes a tiny voltage which makes a
current flow; the greater the temperature difference the greater the current.
● Used for high temperatures which vary rapidly
Liquid-in-glass thermometer:
● As temperature rises or falls, the liquid expands or contracts.
● Amount of expansion can be matched to temperature on a scale.
Sensitivity, range and linearity:
● Sensitivity is the change in length per change in temperature.
○ To increase the sensitivity of a thermometer, use a bigger bulb or a narrower
bore.
● Range is the difference between maximum and minimum temperatures.
○ To increase the range of a thermometer, use a wider bore or a longer stem.
● Linearity is when a given change in temperature causes the same change in length.
Fixed points are used to calibrate thermometers. For example, the fixed points of the celsius scale
are the melting point and the boiling point of water.
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Thermal processes
Conduction
●
●
●
Thermal energy in solids and liquids can be transferred by conduction.
Non-metals are usually poor conductors known as insulators. As a non-metal is
heated up, the molecules vibrate more and cause adjacent molecules to vibrate more
also, transferring heat energy from hot parts to cooler parts.
Metals are usually good conductors. The electrons can leave the atoms and move
freely among positively charged ions. As the metal is heated, the ions and electrons
vibrate more. The free electrons collide with ions throughout the metal and transfer
heat energy from hot parts to cooler parts.
Convection
●
●
●
●
Thermal energy in fluids (liquids and gases) can be transferred by convection.
Convection occurs when molecules in a fluid with high thermal energy move to an area with
low thermal energy.
When part of a fluid is heated, it expands and becomes less dense. It therefore rises up to
less dense areas in the fluid. Denser, colder fluid falls down to take its place.
Examples of convection include water boilers and hot air balloons.
Radiation
●
●
●
Thermal energy is also transferred by infrared radiation which does not require a medium.
Infrared radiation is part of the electromagnetic spectrum.
Black bodies with a dull texture are the best absorbers and emitters of radiation. White
bodies with a shiny texture are the best reflectors of radiation.
The higher the temperature and the greater the surface area of a body the more
infrared radiation emitted.
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Definitions and Concepts for CAIE Physics GCSE
Topic 3: Properties of Waves, Including Light
and Sound
Definitions in ​bold ​are for extended students only
3.1 General Wave Properties
Amplitude: ​The maximum displacement of a wave from its undisturbed (equilibrium)
position.
Diffraction: ​It is the bending of waves around gaps or corners. ​It occurs when the size of
the aperture or obstacle is of the same order of magnitude as the wavelength of the
incident wave.
Frequency: ​The number of waves passing a given point in a second. It is the inverse of the
wave’s time period.
Longitudinal waves​: Waves with oscillations that are parallel to the direction of
travel/energy transfer.
Reflection​: The bouncing back of a wave at a boundary.
Refraction​: The changing of speed, and consequently the direction, of a wave as it changes
medium. The wavelength of the wave will also change but the frequency remains constant.
Speed of a wave: ​The speed is the distance traveled by a given point on the wave in a given
interval of time.
Transverse waves​: Waves with oscillations that are perpendicular to the direction of
travel/energy transfer.
Vibration: ​Is a mechanical phenomenon whereby oscillations occur about an equilibrium
point.
Water waves: ​They are waves propagating on the water surface.
Wave: ​A process of energy transfer through oscillations, without matter being transferred
with it.
Wavefront: ​An imaginary surface representing points of a wave that are at the same point in
their cycle.
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Wavelength: ​The distance from a point on one wave to the same point on the adjacent wave
(ie. peak to peak or trough to trough).
3.2 Light
3.2.1 Reflection of Light
Angle of incidence: ​The angle which an incident line or ray makes with a perpendicular to
the surface at the point of incidence.
Angle of reflection: ​The angle made by a reflected ray with a perpendicular to the reflecting
surface.
Optical image: ​It is the apparent reproduction of an object, formed by a lens or mirror
system from reflected, refracted, or diffracted light waves.
Plane mirror: ​It is a flat reflective surface.​ The image formed by a plane mirror is always
virtual, upright, and of the same shape and size as the object it is reflecting.
3.2.2 Refraction of Light
Critical angle: ​The angle of incidence beyond which all the wave is totally internally reflected
when it meets a boundary.
Optical fibres​:​ A thin flexible fibre with a glass core through which light signals can be
transmitted along its axis, by the process of total internal reflection.
Parallel: ​Two lines that are always the same distance apart and never meet.
Refractive Index​: ​The ratio of the speed of the wave in a vacuum to the speed of the
wave in a given medium.
Transparent: ​A material allowing light to pass through.
Total internal reflection: ​The process of all a wave being reflected when it meets a
boundary. It occurs when the angle of incidence is greater than the critical angle, and only
when going from a higher refractive index to a lower one.
3.2.3 Thin Converging Lens
Diminished: ​Made smaller or less.
Enlarged: ​Having become or been made larger.
Focal length: ​Is the distance between the centre of the lens and the principal focus.
Focus: ​Is the point where light rays originating from a point on the object converge.
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Magnifying glass​: It is a convex lens that lets the observer see a larger image of the
object under observation.
Principal focus: ​Is the point where rays of light travelling parallel to the principal axis
intersect the principal axis and converge.
Real Image​: An image produced by light-rays physically converging. Real images are ones
that can be projected onto a screen.
Single lens: ​A lens that consists of a single piece of transparent material.
Thin converging lens: ​Lens that​ ​focuses the diverging, or blurred, light rays from a distant
object by refracting (bending) the rays.
Virtual image: ​An image produced by the apparent, but not actual, divergence of
light-rays. Virtual images cannot be projected onto a screen.
3.2.4 Dispersion of Light
Dispersion: ​Is defined to be the spreading of white light into its full spectrum of wavelengths.
Glass prism: ​Is a transparent optical element with flat, polished surfaces that refract light.
Monochromatic light:​ ​Is light where the optical spectrum contains only a single optical
frequency.
Spectrum: ​Is the range of frequencies of electromagnetic radiation and their respective
wavelengths and photon energies.
3.3 Electromagnetic Spectrum
Electromagnetic spectrum: ​A group of transverse waves that cover a large range of
frequencies and wavelengths. The highest frequency waves in the spectrum are gamma-rays
and the lowest are radio waves. ​Speed of electromagnetic waves in a vacuum is 3.0 × 10​8
m/s and is approximately the same in air.
Infrared: ​Used for cooking food, thermal imaging and short range communications. It can
cause skin burns.
Microwaves:​ Used for satellite communications and for cooking food. They can cause
internal heating of body cells.
Radio Waves: ​Used for television and radio signals. ​They can be produced by
oscillations in electrical circuits, or can induce these oscillations themselves.
Vacuum​: ​Space in which there is no matter
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Wavelength:​ The distance from a point on one wave to the same point on the adjacent wave
(ie. peak to peak or trough to trough).
X-Rays: ​Used for medical imaging and security scanners. They can cause cell damage and
mutations.
3.4 Sound
Audible frequencies: ​It is a periodic vibration whose frequency is in the band audible to the
average human, the human hearing range, which is 20Hz to 20000Hz
Compressions​: ​They are regions of high pressure due to particles being close together.
Echo​:​ Is a distinct, reflected sound wave from a surface.
Loudness:​ ​A measure of the amplitude of the oscillations of a sound wave. The larger the
amplitude, the louder the sound will be.
Pitch​: ​A measure of the frequency of the oscillations of a sound wave. The higher the
frequency, the higher the pitch of the sound.
Rarefactions​: They are regions of low pressure due to particles being spread further apart.
Sound waves:​ ​The longitudinal waves responsible for sound. They are produced by
vibrating sources and they require a medium to travel through, transmitted by the vibrations
of the medium’s particles.
Speed of sound​: The speed of sound is the distance travelled per unit of time by a sound
wave as it propagates through a medium.
Ultrasound waves: ​Waves that have a frequency higher than the upper limit of human
hearing (20kHz).
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CIE Physics IGCSE
Topic 3: Waves
Summary Notes
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General wave properties
Waves transfer energy without transferring matter; particles oscillate about a fixed point.
Amplitude
Wavelength
Frequency
Speed
– the distance from the equilibrium position to the maximum displacement
– the distance between a point on one wave and the same point on the next wave
– the number of waves that pass a single point per second
– the distance travelled by a wave each second
●
Speed is related to frequency and wavelength
by: 𝒔𝒑𝒆𝒆𝒅 = 𝒇𝒓𝒆𝒒𝒖𝒆𝒏𝒄𝒚 × 𝒘𝒂𝒗𝒆𝒍𝒆𝒏𝒈𝒕𝒉
𝒗 = 𝒇𝝀
Types of waves:
● Transverse waves
○ Has peaks and troughs
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○ Vibrations are at right angles to the direction of
travel
○ An example is light
● Longitudinal waves
○ Consists of compressions (particles pushed together) and rarefactions
(particles moved apart)
○ Vibrations are in the same direction as the direction of travel
○ An example is sound
A wavefront is a surface containing points affected in the same way by a wave at a given time such
as crests or troughs.
Reflection:
● Waves reflect off smooth, plane surfaces rather than
getting absorbed
○ Angle of incidence = angle of reflection
● Rough surfaces scatter the light in all directions, so they
appear matte and unreflective
● Frequency, wavelength, and speed are all unchanged
Refraction:
● The speed of a wave changes when it enters a new medium
● If the wave enters a more optically dense medium, its speed
decreases and it bends towards the normal
● If the wave enters a less optically dense medium, its speed
increases and it bends away from the normal
● In all cases, the frequency stays the same but the wavelength
changes.
Diffraction:
● Waves spread out when they go around the sides of
an obstacle or through a gap
● The narrower the gap or the greater the
wavelength, the more the diffraction
● Frequency, wavelength, and speed are all unchanged
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Light
Reflection
●
When light is reflected off a plane mirror, it forms an
image with these characteristics:
○ Upright
○ Same distance from the mirror as the object
○ Same size
○ Virtual
Refraction
●
●
●
●
Refraction can be shown when light is passed through a
glass slab at an angle to its normal
When light enters a more optically dense medium, the
Denser medium
angle of incidence (the angle between the incident ray
and the normal) is greater than the angle of refraction
(the angle between the refracted ray and the normal).
The opposite is true when light enters a less optically
dense medium.
The refractive index n of a medium is defined as the ratio between the speed of light
𝑠𝑝𝑒𝑒𝑑 𝑜𝑓 𝑙𝑖𝑔ℎ𝑡 𝑖𝑛 𝑣𝑎𝑐𝑢𝑢𝑚
in a vacuum and the speed of light in the medium:𝑛 = 𝑠𝑝𝑒𝑒𝑑 𝑜𝑓 𝑙𝑖𝑔ℎ𝑡 𝑖𝑛 𝑡ℎ𝑒 𝑚𝑒𝑑𝑖𝑢𝑚
Snell's law relates the angle of incidence and the angle of refraction to the refractive
𝑠𝑖𝑛 𝑖
index by: 𝑛 = 𝑠𝑖𝑛 𝑟 where i is the angle of incidence and r is the angle of refraction.
Total internal reflection:
● At a certain angle of incidence called the critical angle, the light
will travel along the boundary between the two media.
● Total internal reflection occurs when the angle of incidence is
greater than the critical angle and the light reflects back into the
medium.
● For total internal reflection to occur, the light must also be
travelling from a more optically dense medium into a less
optically dense medium (most common example is glass to air).
● The critical angle can be related to the refractive index by:
1
𝑛=
𝑠𝑖𝑛 𝑐
Optical fibres:
● An optical fibre is a long thin rod
of glass surrounded by cladding
which uses total internal
reflection to transfer information
by light, even when bent.
● Extensive use in medicine
(endoscopes, inside-body flexible
cameras) and communications
(high speed data transfer).
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Converging lens:
● A converging lens is a transparent block which brings light rays together at a point called
the principal focus by utilising refraction.
● The focal length is the distance between the centre of the lens and the principal focus.
● The image formed by a converging lens can be either real or virtual.
○ Real images are formed when the distance of the object from the centre of the
lens is greater than the focal length. They are images where light actually
converges to a position and can be projected onto a screen.
○ Virtual images are formed when the distance of the object from the centre of
the lens is smaller than the focal length. They are images where light only
appears to have converged and they cannot be projected onto a screen.
● You can draw ray diagrams for real images (shown on the left below) and virtual images
(shown on the right below).
●
●
The image formed is enlarged/same size/diminished and upright/inverted.
○ The image on the left above is diminished and inverted.
○ The image on the right above is enlarged and upright.
Converging lenses are used in magnifying glasses and binoculars (to enlarge the image).
Dispersion
When white light is passed through a glass prism, it splits
up into its constituent colours. This happens because the
different colours travel at different speeds in the glass, so
they refract by different amounts.
● The seven colours in order of decreasing
wavelength are red, orange, yellow, green, blue,
indigo and violet (ROYGBIV).
● The greater the wavelength, the slower the speed
in glass and the greater the refractive index.
Light of a single frequency is described as monochromatic.
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Electromagnetic spectrum
Properties of electromagnetic waves:
● Transverse waves
● Do not need a medium
● All electromagnetic waves travel with the same high speed of 3.0 x 108 ms-1 in a vacuum
and approximately the same speed in air.
You need to learn the main groups of the electromagnetic spectrum in order of wavelength.
westernreservepublicmedia.org
As speed is constant for all electromagnetic waves, as wavelength decreases, frequency must
increase. The higher the frequency of an EM wave, the greater its energy.
Uses of electromagnetic waves:
● Radio waves are used for radio and television communications. They have a long
wavelength and are reflected by the ionosphere.
● Microwaves are used for satellite communication and in microwave oven. They pass
through the ionosphere and penetrate deep into food.
● Infrared radiation is used in remote controllers and infrared cameras.
● Visible light is used in fibre optics.
● Ultraviolet light is used in tanning beds.
● X-rays are used in medical imaging and in security as they can penetrate material easily.
● Gamma radiation is used in medical treatment due to its high energy.
Hazards:
● Too much exposure to ultraviolet light skin increases the risk of skin cancer.
○ Sun cream prevents over-exposure in summer.
● X-rays and gamma rays are ionising radiation that can cause mutations leading to cancer.
○ Exposure to these kinds of radiation should be minimised.
● Microwaves can cause internal heating of body tissues.
● Infrared radiation can cause skin burns.
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Sound Waves
Sound waves are longitudinal waves created by vibrating sources. A medium is needed to transmit
sound waves (such as air).
●
●
The greater the amplitude of a sound wave, the louder it is.
The greater the frequency of a sound wave, the higher its pitch.
To measure the speed of sound in air, you can make a noise at a known, large distance from a
solid wall and record the time for the echo (reflected sound) to be heard, then use speed =
distance/time, taking into account the fact that the sound had to go there and back.
The speed of sound in air is 343 ms-1, the speed of sound in water is 1493 ms-1, and the
speed of sound in steel is 5130 ms-1.
The range of audible frequencies for a healthy human ear is 20 Hz to 20000 Hz. Ultrasound is
sound with a frequency greater than 20000 Hz:
● When ultrasound reaches a boundary between two media it is partially reflected back. The
remainder of the waves continue to pass through.
● A transceiver can emit ultrasound and record the reflected waves to find the distance of
things below the surface.
● Ultrasound is used for things such as SONAR and for medical imaging without using
ionising radiation.
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Definitions and Concepts for CAIE Physics GCSE
Topic 4: Electricity and Magnetism
Definitions in bold are for extended students only
4.1 Simple Phenomena of Magnetism
Alternating current: Current flow consisting of charges that continually change
direction. These oscillations usually occur at a set frequency.
Bar magnet: Is a rectangular piece of an object that shows permanent magnetic
properties.
Demagnetisation: Process of removing magnetic qualities in a material.
Direct current: Current flow consisting of charges flowing in a single direction
only. Batteries and cells provide direct current.
Electromagnet: A solenoid with an iron core. The magnetism of an electromagnet can
be switched on and off, and the strength changed, through varying the current in the
solenoid.
Induced magnet: A material that becomes a magnet when it is placed in an
existing magnetic field, but loses its magnetism quickly once it is removed.
Induced magnetism always produces attractive forces.
Magnet : A magnet is a material or object that produces a magnetic field.
Magnetisation: Process of inducing magnetic qualities in a material.
Magnetic field: The region around a magnet in which another magnet or
magnetic material will experience a force.
Magnetic field lines: Lines that show the strength and direction of a magnetic field.
The lines point from North to South and their concentration represents the magnitude
of the field
Magnetic materials: Iron, steel, cobalt and nickel.
Non-magnetic materials: Materials which are not attracted by a magnet.
Permanent magnet: A magnet that produces its own magnetic field.
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4.2 Electrical Quantities
4.2.1 Electric Charge
Charging by induction: Is a method used to charge an object without actually
touching the object to any other charged object.
Conductor: A material that allows electrical charge to flow easily. Metals are
particularly good conductors due to the free electrons in their structures.
Coulomb: The unit of charge.
Electric charge: Is the physical property of matter that causes it to experience a
force when placed in an electromagnetic field. There are two types of electric
charges: positive and negative.
Electric field: A region in which a charge will experience a non-contact,
electric force. All charged objects have an electric field around them, and
this field is stronger the closer you are to the charge.
Electrostatic charge - The electric charge at rest on the surface of an insulated body.
Insulator: A material that doesn’t allow electrical charge to flow.
Like charges: When two charges of the same polarity meet, they will repel.
Point charge: The electric field around a point charge becomes weaker the
further away you are. The field lines for a positive charge point radially
outwards, whereas the field lines for a negative charge point radially
inwards.
Unlike charges: When two charges of opposite polarities meet, they will attract.
4.2.2 Current
Ammeter: A device connected in series with a component to measure the current that
flows through it
Analogue device: A measuring device that requires the user to read from a scale
to obtain the measurement.
Conventional current: Is defined as moving in the same direction as the
positive charge flow.
Digital device: A measuring device that displays the measurement on a display, rather
than requiring the user to read from a scale..
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Electric Current: The rate of flow of electrical charge. Its value is the same at any
position in a single closed loop. In metals, the charges that flow are electrons.
4.2.3 Electromotive Force
Electromotive force: The energy supplied by a source in driving charge
round a complete circuit. Measured in Volts.
Volt: The unit of potential difference (voltage). One volt is equal to one joule per
coulomb.
4.2.4 Potential Difference
Potential difference: The energy that is transferred per unit charge between
two points in a circuit. It is often also called a voltage and measured in volts.
Voltmeter: A device that is connected in parallel with a component to measure the
potential difference (voltage) across it.
4.2.5 Resistance
Ammeter: A device connected in series with a component to measure the current that
flows through it.
Current–voltage characteristic: Is a relationship, typically represented as a chart
or graph, between the electric current through a circuit and the corresponding
voltage, or potential difference across it.
Filament lamp: A light emitting component consisting of an enclosed metal
filament. Its resistance increases as the filament’s temperature increases.
Ohmic resistor: A resistor that functions according to Ohm's law.
Resistance: A measure of the opposition to current flow. Calculated as ratio of the p.d.
applied to the electric current which flows through it:
4.2.6 Electrical Working
Battery: Is a device that stores chemical energy and converts it to electrical
energy.
Power: The rate at which an appliance transfers energy. For a circuit component, it
is equal to the product of the current passing through it and the potential
difference across it.
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4.3 Electric Circuits
4.3.1 Circuit Diagrams
Circuit diagram: Is a graphical representation of an electrical circuit.
Diode: A component that only allows current to flow through in the forward
direction. They have very large resistances in the reverse direction.
Electric heater: Is an electrical device that converts an electric current into heat.
Filament lamp: A light emitting component consisting of an enclosed metal filament.
Its resistance increases as the filament’s temperature increases.
Fixed resistors: Are the resistors whose resistance does not change with the
change in voltage or temperature.
Fuse: A safety device consisting of a thin metal filament that melts and cuts off the
power supply if there is a surge in current. Fuses are connected to the live wire.
Galvanometer: Is an electromechanical instrument used for detecting and
indicating an electric current.
Light dependent resistor (LDR): A light sensitive component whose resistance
decreases as its temperature increases.
Relay: Is a special type of switch turned on and off by an electromagnet.
Switch: Is a device used for making and breaking electric current through the
circuit.
Thermistor: A temperature dependent component, whose resistance increases
as its temperature decreases.
Transformer: An iron core with a primary and secondary coil of wire wound around
opposite ends. Transformers can change the magnitude of an alternating voltage.
Variable resistor: Is a resistor of which the electric resistance value can be
adjusted.
4.3.2 Series and Parallel Circuits
Parallel: Components connected in parallel have the same potential difference
across each component. The current from the source is larger than the current in
each branch and the total current is equal to the sum of the currents flowing
through each component.
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Resistors in parallel: The total resistance is less than the lowest individual
resistance.
Resistors in series: The total resistance is equal to the sum of the resistances of
the individual resistors.
Series: Components connected in series have the same current passing through
each component but share the total potential difference (voltage) of the power
supply. The sum of the potential difference across the components in a
series circuit is equal to the total potential difference across the supply.
4.3.3 Action and use of Circuit Components
Input transducers: Is a device that takes a form of physical energy and converts
it into a signal which can be read.
Light dependent resistor (LDR): A light sensitive component whose resistance
decreases as its temperature increases.
Rectifier: Is an electrical device that converts alternating current (AC) to
direct current (DC).
Relay: Is a special type of switch turned on and off by an electromagnet.
Switch: Is a device used for making and breaking electric current through the circuit.
Thermistor: A temperature dependent component, whose resistance increases as its
temperature decreases.
Variable potential divider: Is a simple circuit that uses resistors(or thermistors /
LDRs) to supply a variable potential difference.
4.4 Digital Electronics
Analogue: They are electronic systems with a continuously variable signal.
AND gate: Is a logic gate that implements logical conjunction.
Digital: A waveform that switches representing the two states of low and
high.
NAND gate: Is a logical gate which is the opposite of an AND logic gate.
NOR gate: Is a logical gate which is the opposite of an OR logic gate.
NOT gate: Is a logic gate which implements logical negation.
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OR gate: Is a logic gate that implements logical disjunction.
Truth table: Is a mathematical table used in logic which sets out the
functional values of logical expressions on each of their functional
arguments.
4.5 Dangers of Electricity
Circuit breaker: A safety device that cuts off the power supply if a surge of current
passes through it. Circuit breakers can be reset and are quicker acting than fuses.
Earthing: The removal of excess charge by providing a low resistance path for
electrons to flow through.
Fuse: A safety device consisting of a thin metal filament that melts and cuts off the
power supply if there is a surge in current. Fuses are connected to the live wire.
Insulator: A material that doesn’t allow electrical charge to flow.
4.6 Electromagnetic Effects
4.6.1 Electromagnetic Induction
Conductor: A material that allows electrical charge to flow easily. Metals are
particularly good conductors due to the free electrons in their structures.
Electromagnetic induction: Is the production of an electromotive force across an
electrical conductor in a changing magnetic field. The direction of an induced e.m.f.
opposes the change causing it
Induced current: The current induced in a conducting loop that is exposed to a
changing magnetic field
Magnetic field: The region around a magnet in which another magnet or magnetic
material will experience a non-contact force.
4.6.2 a.c. Generator
Alternating current: Current flow consisting of charges that continually change
direction. These oscillations usually occur at a set frequency.
Direct current: Current flow consisting of charges flowing in a single direction only.
Batteries and cells provide direct current.
Generator effect: When there is relative motion between an electrical
conductor and a magnetic field, a potential difference will be induced across
the ends of the conductor. A current will flow if this conductor is part of a
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complete circuit.
Rotating-coil generator: A device consisting of a coil, which when spun in a
magnetic field, induces a current in the coil.
Slip ring: Is an electromechanical device that allows the transmission of
power and electrical signals from a stationary to a rotating structure.
4.6.3 Transformer
High-voltage transmission: Electricity is transported along them at very high voltages
to reduce the energy loss and make the transportation more efficient.
Step-Down transformer: A transformer that has a smaller potential difference in the
secondary coil than in the primary coil. This is a result of the secondary coil having
fewer turns.
Step-Up transformer: A transformer that has a larger potential difference in the
secondary coil than in the primary coil. This is a result of the secondary coil having
more turns.
Transformer: An iron core with a primary and secondary coil of wire wound around
opposite ends. Transformers can change the magnitude of an alternating voltage.
Turns ratio: The number of turns in the primary coil of a transformer over the number
of turns in the secondary coil. This is equal to the voltage ratio for a 100% efficient
transformer.
Voltage ratio: The voltage across the primary coil of a transformer over the voltage
across the secondary coil.
4.6.4 The Magnetic Effect of a Current
Magnetic field: The region around a magnet in which another magnet or magnetic
material will experience a non-contact force. The direction of a magnetic field line at
a point is the direction of the force on the N pole of a magnet at that point.
Relay: Is a special type of switch turned on and off by an electromagnet.
Solenoid: A wire wrapped into the shape of a coil, that has a strong and uniform
magnetic field inside of it. The solenoid’s magnetic field strength can be increased by
adding an iron core.
4.6.5 Force on a Current-Carrying Conductor
Beam of charged particles: Is a spatially localized group of electrically
charged particles that have approximately the same position, kinetic energy,
and direction.
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Charged particle: Is a particle with an electric charge.
Conductor: A material that allows electrical charge to flow easily. Metals are
particularly good conductors due to the free electrons in their structures.
4.6.6 d.c. Motor
Electric motor: A current-carrying coil of wire in a magnetic field. The two sides of the
coil that are perpendicular to the magnetic field experience forces in opposite
directions, causing rotation.The effect is increased by increasing the number of turns
on the coil, increasing the current, or increasing the strength of the magnetic field
Split-ring commutator: Device used to reverse the direction of the current in
the coil each half turn. This allows the motor coil to rotate continuously in
one direction.
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CIE Physics IGCSE
Topic 4: Electricity and Magnetism
Summary Notes
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Simple phenomena of magnetism
Magnetic forces are due to interactions between magnetic fields. In a magnet, like poles repel
and opposite poles attract.
●
●
Magnetic materials are materials that are attracted to magnets
and can be magnetised (e.g. iron, steel, cobalt, nickel)
Non-magnetic materials are materials that are not attracted to
magnets and cannot be magnetised (e.g. glass, plastic)
Induced magnetism:
● Magnetic materials can be magnetised by induced magnetism:
○ They can be magnetised by stroking them with a
magnet, hammering them in a magnetic field, or putting
them inside a coil with a direct current through it.
○ They can be demagnetised by hammering them,
heating them or putting them inside a coil with an
alternating current through it.
● Magnetic materials that can be permanently magnetised are
described as magnetically hard (e.g. steel). Magnetic materials that are only temporarily
magnetised are described as magnetically soft (e.g. soft iron).
Permanent magnets vs electromagnets:
● Permanent magnets are a hard-magnetic material that has been permanently magnetised
whereas electromagnets consist of a coil of wire wrapped around a magnetically soft core
and can be turned on and off.
● Permanent magnets are more useful when they do not need to be turned off such as a
fridge magnet, whereas electromagnets have the ability to be turned on and off so they can
be used for situations such as moving scrap metal.
Magnetic fields:
● Field lines around a bar magnet point from north to south
● The direction of a magnetic field line shows the
direction of the force on a north pole at that point.
● Field strength decreases with distance from the magnet
● Plotting compasses are small compasses which show the
direction and shape of a magnetic field.
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Electrical quantities
Electric charge
Charge is measured in coulombs. There are positive and negative charges; unlike charges
attract and like charges repel.
● Charging a body involves the addition or removal of electrons.
● Conductors allow electrons to flow through them whereas insulators impede the flow of
electrons.
○ Conductors such as metals are used as wires in circuits.
○ When two insulators are rubbed together, electrons move from one to the other and
they become charged. For example, when a rod is rubbed with a cloth, electrons are
transferred from the rod onto the cloth and the rod becomes positively charged.
● Charge can be detected using a gold leaf electroscope.
○ If a positively charged rod is brought close to the
disc on top of the electroscope, electrons are
attracted to the top of the disc, away from the
bottom of the metal stem and the gold leaf. The
gold leaf will then be repelled from the metal stem
because they both become positively charged.
○ If someone then touches the disc, electrons
flow from the ground into the disc as they are
attracted to the rod, and the electroscope now
contains a net negative charge. This is called
charging by induction.
Charges create electric fields (regions in which an electric charge experiences a force); the
direction of an electric field at a point is the direction of the force on a positive charge at
that point.
● Electric field lines point away from positive charges and
towards negative charges.
○ The field lines around a charged conducting
sphere are as if the charge was concentrated at
the centre of the sphere.
○ The field lines between two charged plates go in
straight lines from the positive plate to the
negative plate and are equally spaced apart.
Current
Current I is measured in amps and is the rate of flow of charge at a point in the circuit.
● The current is given by I=Q/t.
● It is measured with an ammeter placed in series.
● In metals, current is due to a flow of electrons. Because electrons are negatively
charged, conventional current (which is the rate of flow of positive charge) is in the
opposite direction to the flow of electrons.
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Electromotive force
The electromotive force (e.m.f) of an electrical source of energy is measured in volts and is the
energy supplied by the source per unit charge in driving the charge round a complete
circuit.
Potential difference
Potential difference V is measured in volts (1 V = 1 JC-1) and is the work done per unit charge in
moving between two points in a circuit.
● It is measured with a voltmeter placed in parallel across the component.
● The higher the potential difference, the greater the current.
Resistance
The resistance of a component is given by the potential difference across it divided by the current
through it. The greater the resistance, the harder it is for current to flow through the component.
● As the length of a resistor increases, the resistance increases.
○ The resistance is directly proportional to the length.
● As the diameter of a resistor increases, the resistance decreases.
○ The resistance is inversely proportional to the cross-sectional area.
In an ohmic conductor, the current is directly proportional to the voltage (i.e. it has constant
resistance). In a non-ohmic conductor (such as a filament lamp), the resistance changes as the
voltage and current change.
As the current increases through a filament lamp, so does the temperature. This means
electrons and ions vibrate more and collide more, increasing resistance.
Electrical working
●
●
●
Energy is transferred from chemical energy in the battery to electrical energy used by circuit
components and then to the surroundings.
The power of a component is given by P=IV.
By using V=IR, this can be shown to be equivalent to P=I2R and P=V2/R.
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Electric circuits
Series:
● Components are connected end to end in one loop
● The same current flows through every component
● The potential difference is shared across each component (i.e. the sum of the p.d.s across
the components is equal to the total p.d. across the supply).
● The total resistance is the sum of the resistances of each component RT = R1 + R2 + …
● The combined e.m.f. of several sources in series is the sum of the individual e.m.f.s
Parallel
● Components are connected to the power supply in separate branches
● The current is shared between each branch (i.e. the sum of the currents in the separate
branches is equal to the current through the source)
● The potential difference is the same across every branch
● The total resistance of two resistors in parallel is less than the resistance of either resistor
𝟏
𝟏
𝟏
by itself, and is given by 𝑹 = 𝑹 + 𝑹
●
𝑻
𝟏
𝟐
Connecting lamps in parallel is advantageous because if one breaks, current can still pass
through the rest.
A potential divider circuit divides the source voltage
into smaller parts.
● The voltage across a certain component is
𝑅
given by𝑉𝑜𝑢𝑡 = 𝑉𝑖𝑛 × 𝑅 where Vin is the
𝑇
source voltage, R is the resistance of the
component and RT is the total resistance.
A thermistor is a resistor whose resistance decreases
as the temperature increases.
A light dependent resistor is a resistor whose
resistance decreases as light intensity increases.
A relay is an electromagnetically operated switch.
When a small current passes through the
electromagnet, it switches on and attracts an iron
arm. This arm rotates about a pivot and pushes the
contacts in another circuit together.
● They are used to switch on a circuit with a
high current using a circuit with a small
current.
The above three components can be used in
conjunction to operate light-sensitive switches
and temperature-operated alarms.
Diodes only allow current to flow in one
direction, because they have a very high
resistance in the other direction. They can be
used as a rectifier (i.e. convert AC into DC).
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Digital electronics
●
●
Analogue signals vary continuously in amplitude, frequency or both.
Digital signals are a series of pulses with two states, a high state and a low state.
Digital signals carry more information per second and maintain their quality better
over longer distances compared to analogue signals.
○ All signals get weaker as they travel longer distances and need to be
amplified so they can be returned to the original. Noise in analogue signals is
amplified too when the signal is amplified, so the quality is reduced. However,
in digital signals, the noise is normally a lower amplitude than the high/low
states used, so it can be ignored.
Logic gates:
NOT gate
AND gate
OR gate
NAND gate
NOR gate
If the input is
one state, the
output will be
the other state.
If both of the
inputs are high,
the output will
be high;
otherwise the
output will be
low.
If either of the
inputs is high,
the output will
be high;
otherwise the
output will be
low.
If both of the
outputs are
high, the output
will be low;
otherwise the
output will be
high.
If either of the
inputs is high,
the output will
be low;
otherwise the
output will be
high.
The symbols for the logic gates are shown in the diagram on the page above. Truth tables
show the corresponding output of one or more gates given all possible inputs.
Dangers of electricity
Hazards:
●
●
●
Damaged insulation – contact with the wire due to gaps in the insulation can cause an
electric shock or pose a fire hazard by creating a short circuit.
Overheating of cables – high currents passing through thin wire conductors cause the wires
to heat up to very high temperatures which could melt the insulation and cause a fire.
Damp conditions – water can conduct a current so wet electrical equipment can cause an
electric shock.
Fuses:
●
●
A fuse is a thin piece of wire which overheats and melts if the current is too high, protecting
the circuit.
Fuses have a current rating which should be slightly higher than the current used by the
device in the circuit. The most common are 3A, 5A and 13A.
Circuit breakers:
●
●
Circuit breakers consist of an automatic electromagnet switch which which breaks the
circuit if the current rises over a certain value.
This is better than a fuse as it can be reset and used again, and they operate faster.
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Earthing metal cases:
●
●
Earth wires creates a safe route for current to flow through in the case of a short circuit,
preventing electric shocks.
Earth wires have a very low resistance so a strong current surges through them which
breaks the fuse and disconnects the appliance.
Electromagnetic effects
Electromagnetic induction
●
●
●
●
●
When a wire moves across a magnetic field, an e.m.f. is
induced in it. If it is part of a complete circuit, this causes a
current to flow.
The induced current flows in such a direction that it
opposes the change that produced it.
The induced e.m.f. can be increased by moving the wire
more quickly, using a stronger magnetic field, or increasing the length of the wire.
The direction of the e.m.f. is determined by Fleming’s right hand rule as shown in the
diagram.
An e.m.f. is also induced if a changing magnetic field links with a conductor. For example,
when a magnet is moved into a coil, the magnetic field through the coil changes and an
e.m.f. is induced in it. The more quickly the magnetic field changes, the greater the e.m.f.
AC generator
●
●
●
●
●
In a direct current, the current only flows in one direction whereas in an alternating current,
the current continuously changes direction.
An AC generator consists of a coil of wire between two permanent magnets. They
generate AC current because a slip ring commutator is used.
As the coil rotates, the magnetic field through the coil changes, which induces an
e.m.f. in the coil.
The magnitude of the e.m.f. is maximum
when the coil is horizontal as the field
lines are cut the fastest, and zero when
vertical as no field lines are being cut.
The e.m.f. can be increased by increasing
the number of turns on the coil,
increasing the area of the coil, using a
stronger magnet or increasing the speed
of rotation.
Transformer
●
●
A transformer consists of two coils wrapped around a soft iron core and is used to
transform voltages.
An alternating current in the primary coil creates a changing magnetic field; this
changing magnetic field links with the secondary coil and induces an alternating
e.m.f. in it.
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●
●
●
●
A step up transformer has more turns on the secondary which means the voltage of the
secondary is greater than that of the primary. A step down transformer has fewer turns on
the secondary which means the voltage of the secondary is less than that of the primary.
𝑁𝑝𝑟𝑖𝑚𝑎𝑟𝑦
𝑉
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑜𝑖𝑙𝑠 𝑜𝑛 𝑝𝑟𝑖𝑚𝑎𝑟𝑦
𝑝𝑑 𝑜𝑓 𝑝𝑟𝑖𝑚𝑎𝑟𝑦
=
= 𝑝𝑟𝑖𝑚𝑎𝑟𝑦
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑜𝑖𝑙𝑠 𝑜𝑛 𝑠𝑒𝑐𝑜𝑛𝑑𝑎𝑟𝑦
𝑝𝑑 𝑜𝑓 𝑠𝑒𝑐𝑜𝑛𝑑𝑎𝑟𝑦
𝑁𝑠𝑒𝑐𝑜𝑛𝑑𝑎𝑟𝑦
𝑉𝑠𝑒𝑐𝑜𝑛𝑑𝑎𝑟𝑦
For a 100% efficient transformer, because the power used is constant, 𝐼𝑝 𝑉𝑝 = 𝐼𝑠 𝑉𝑠
Transformers are used to step up the voltage in power lines which reduces power loss.
This is because a higher voltage means a smaller current and the loss of power due
to P=I2R will be lower.
The magnetic effect of a current
●
●
●
●
The right hand grip rule determines the
direction of the magnetic field produced by a
current carrying wire.
The magnetic field created by a solenoid is
like the field produced by a bar magnet.
Increasing the current through the wire
increases the strength of the magnetic
field, and reversing the direction of the
current through the wire reverses the
direction of the magnetic field.
The magnetic effect of current is used in
relays.
Force on a current-carrying conductor
●
●
●
A force acts on a current-carrying conductor in a
magnetic field. Fleming’s left hand rule shows the
relative directions of the force, field, and current.
○ If a current-carrying wire is fixed in place
between two magnets which rest on a balance,
the wire will exert an equal and opposite force
on the magnets and the reading will change,
showing that a force is acting.
If the current is reversed or the magnetic field is
reversed, the force will be reversed.
A force is also exerted on charged particles moving
in a magnetic field (because moving charged particles are current). If a beam of
charged particles moves through a magnetic field, it will be deflected, showing that
there is a force.
DC motors
●
●
●
DC motors consist of a coil of wire in between two permanent magnets.
Current flows through the wire and it experiences a turning effect due to the forces exerted
on it in the magnetic field. The turning effect can be increased by:
○ increasing the current
○ using a stronger magnetic field
○ increasing the number of turns on the coil.
A split ring commutator is used to ensure that the direction that the current flows in
the coil reverses every half turn.
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Definitions and Concepts for CAIE Physics GCSE
Topic 5: Atomic Physics
Definitions in ​bold ​are for extended students only
5.1 The Nuclear Atom
5.1.1 Atomic Model
Alpha particle: ​A positively charged particle consisting of two protons and two
neutrons. They are highly ionising, but can be stopped by a few centimetres of
air.
Atom: ​The smallest component of an element having the chemical properties of
the element, consisting of a nucleus containing combinations of neutrons and
protons and one or more electrons bound to the nucleus by electrical attraction.
Electrons: ​A negatively charged constituent of the atom, that are found in different
energy levels, around the nucleus.
5.1.2 Nucleus
Isotopes: ​Atoms with the same number of protons but different numbers of neutrons.
The atomic number is the same, but the mass number is different.
Nuclear fission: ​The splitting of a large and unstable nucleus into two smaller
and more stable nuclei to produce energy. This is the method currently used in
nuclear power stations.
Nuclear fusion:​ ​The joining of two small, light nuclei to form a larger, heavier
one and release energy. It cannot happen at low pressures and temperatures
since in these conditions the electrostatic repulsion of protons in the
nucleus cannot be overcome.
Nucleon number: ​The number of protons and neutrons in an atom.
Nucleus: ​Is a collection of particles called protons, which are positively charged,
and neutrons, which are electrically neutral.
Nuclide: ​Refers to an atom with a distinct number of protons and neutrons in its
nucleus.
Nuclide notation​: Is a shorthand method of showing information about atoms.
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Proton number: ​The number of protons found in an atom of a specific element. Each
element has a different proton number.
5.2 Radioactivity
5.2.1 Detection of Radioactivity
Background radiation: ​Radiation that is found in small quantities all around us and
originates from natural sources such as rocks and cosmic rays, as well as from
man-made sources such as nuclear weapons testing and accidents.
Beta particle: ​A high speed electron that a nucleus emits when a neutron converts
into a proton. ​They are ionising but can be stopped by a thin sheet of aluminium.
Gamma ray:​ Electromagnetic radiation emitted from a nucleus. They have a very high
penetrating power and require several centimetre of lead to absorb them.
5.2.2 Characteristics of the three kinds of Emission
Ionisation​: The process in which an electron is given enough energy to
break away from an atom.
Random nature of radioactive decay: ​You cannot predict which nuclei in a
radioactive sample will decay next, or when the next decay will occur - it is a random
process.
5.2.3 Radioactive Decay
Radioactive decay: ​The random process involving unstable nuclei emitting radiation
to become more stable. During α- or β-decay the nucleus changes to that of a different
element.
5.2.4 Half-Life
Half life: ​The time it takes for the number of unstable nuclei of an isotope in a
sample to halve, or the time it takes for the initial count rate of a sample of the
isotope to halve. It is different for different isotopes.
5.2.5 Safety Precautions
Ionising radiation: ​Radiation that can cause cell mutations, damage cells and tissues,
and lead to cancers.
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CIE Physics IGCSE
Topic 5: Atomic Physics
Summary Notes
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The nuclear atom
An atom consists of:
● A positively charged nucleus made of:
○ Positive protons
○ Neutral neutrons
● Surrounded by negatively charged electrons which orbit the nucleus
The radius of the nucleus is a lot smaller than the radius of the entire atom. Almost all the mass of
the atoms lies in the nucleus.
Particle
Proton
Neutron
Electron
Relative Mass
1
1
0.0005
Relative Charge
+1
0
-1
Atoms of the same element have the same number of protons. Isotopes are forms of an element’s
atom with the same number of protons but a different number of neutrons.
For a given nuclide 𝑍𝐴 𝑋 :
● X is the symbol of the element
● A is the nucleon number (number of neutrons and protons)
● Z is the proton number (number of protons)
Alpha particle scattering:
● An early model of the atom proposed by JJ Thomson
was the plum pudding model - that the atom consisted
of a cloud of positive charge with negatively charged
electrons dotted around inside it.
● In Rutherford’s scattering experiment, he aimed a beam
of alpha particles at a thin gold foil. He concluded that:
○ The atom was composed primarily of empty space
because most alpha particles passed straight through.
○ It had a nucleus which was massive and contained most
of the mass of the atom because it deflected some alpha
particles straight back.
○ The nucleus was positively charged because it repelled
the positively charged alpha particles.
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Nuclear fission:
● The process of splitting a nucleus is called nuclear fission
● Uranium-235 is a commonly used isotope as the fuel in nuclear reactors
● When a Uranium-235 nucleus absorbs a neutron, it splits into two daughter nuclei
and 2 or 3 neutrons, releasing energy in the process
● The neutrons then can induce further fission events in a chain reaction
Nuclear fusion:
● The process of fusing two nuclei to form a larger nucleus is called nuclear fusion
● Energy is released during this process
● Nuclear fusion is how the sun and other stars release energy
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Radioactivity
Radioactive decay is the spontaneous transformation of an unstable nucleus into a more stable
one by the release of radiation. It is a random process which means one cannot know what
nucleus will decay and when it will decay because it is down to chance.
Decay processes:
●
Alpha:
○ A heavy nucleus emits an alpha particle (helium nucleus).
○ The nucleus changes to that of a different element according to the following
𝐴
○
●
𝐴−4
𝑌+
4
𝛼
○
Beta:
○ A neutron turns into a proton and emits a beta particle (electron)
○ The nucleus changes to that of a different element according to the following
𝐴
●
𝑋→
equation:
𝑍
𝑍−2
2
They are highly ionising and weakly penetrating. They are stopped by a sheet of
paper.
They are slightly deflected by electric and magnetic fields.
𝑋→
𝐴
𝑌+
0
𝑒−
equation:
𝑍
𝑍+1
−1
○ They are moderately ionising and moderately penetrating. They are stopped by a
thin sheet of aluminium.
○ They are greatly deflected by electric and magnetic fields.
Gamma:
○ After a previous decay, a nuclei with excess energy emits a gamma particle.
○ Gamma particles are a form of electromagnetic radiation.
○ They are lowly ionising and highly penetrating. They are stopped by many
centimetres of lead.
○ They are not deflected by electric and magnetic fields.
Some ways of detecting radiation include:
● Photographic film:
○ The more radiation absorbed by the film, the darker it gets (the film is initially white).
○ They are worn as badges by people who work with radiation, to check how much
exposure they have had.
● Geiger-Muller tube:
○ A Geiger-Muller tube is a tube which can detect radiation.
○ Each time it absorbs radiation, it transmits an electrical pulse to the machine, which
produces a clicking sound. The greater the frequency of clicks, the more radiation
present.
● Cloud chamber:
○ A cloud chamber is a small container full of water vapour.
○ Alpha particles create short, broad tracks while beta particles produce long, wispy
tracks.
Weak radiation that can be detected from external sources is called background radiation. Sources
of background radiation include:
● Cosmic rays
● Radiation from underground rocks
● Nuclear fallout
● Medical rays
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●
●
●
The half-life of an isotope is
the time taken for half the
nuclei to decay, or the time
taken for the activity to
halve.
In the graph, the count rate
drops from 80 to 40 counts
per minute in 2 days, which
means the half-life is
around 2 days.
Background radiation
has to be subtracted
before attempting to
perform half-life
calculations
Uses of radioactivity:
● Smoke detectors
○ Long half life alpha emitters are used in smoke detectors.
○ Alpha particles cause a current in the alarm.
○ If smoke enters the detector, some of the alpha particles are absorbed and the
current drops, triggering the alarm.
● Thickness monitoring
○ Long half life beta emitters can be used for thickness monitoring of metal
sheets.
○ A source and receiver are placed on either side of the sheet during its
production. If there is a drop or rise in the number of beta particles detected,
then the thickness of the sheet has changed and needs to be adjusted.
● Sterilisation of equipment
○ Gamma emitters are used to kill bacteria or parasites on equipment so it is
safe for operations.
● Diagnosis and treatment
○ Short half life gamma emitters such as technetium-99m are used as tracers in
medicine as they concentrate in certain parts of the body.
■ The half life must be long enough for diagnostic procedures to be
performed, but short enough to not remain radioactive for too long.
○ Other gamma emitters such as cobalt-60 can be used to destroy tumours with
a high dose of radiation.
Exposure to radiation can destroy living cell membranes by ionisation, causing the cells to die, or
damage DNA which causes mutations that could lead to cancer.
Safety measures include:
● Minimising the time of exposure to radiation. For example, radioactive tracers with a short
half life should be used.
● Keeping as big a distance from the radioactive source as possible. They should be handled
using tongs and held far away from people.
● Using shielding against radiation, such as the concrete shielding around a nuclear reactor.
Radioactive sources must also be kept in a lead-lined box.
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iGCSE CIE Physics 0625 (2020 Syllabus) Formula List
General
Average speed (ms-1) = distance (m)
time (s)
Average velocity (ms-1) = displacement (m)
time (s)
v=s
t
Period of a pendulum (s) =
T=
total time (s)
number of swings
t
number
Acceleration (ms-2) = final velocity (ms-1) – initial velocity (ms-1)
time (s)
a = v-u
t
Weight (N) = mass (kg) × gravitational field strength (ms-2)
Note: Earth’s gravitational field strength = 10 ms-2
F = mg
Force (N) = mass (kg) × acceleration (ms-2)
F = ma
-3
Density (kgm ) = mass (kg)
volume (m3)
ρ=M
V
Hooke’s law: Force (N) = constant (Nm-1) × extension (m)
F = kx
Pressure (Pa) = force (N)
area (m2)
P=F
A
Fluid Pressure (Pa) = density (kgm-3) × gravitational field strength (ms-2 or Nkg-1) × height (m) P = ρgh
Work (J) = force (N) × distance moved (m)
ΔE = Fd
Power (W) = work (J)
time (s)
P = ΔE
t
Kinetic Energy (J) = ½ × mass (kg) × velocity2 (ms-1)
KE = ½mv2
Gravitational potential energy (J)
= mass (kg) × gravitational field strength (ms-2 or Nkg-1) × height (m)
GPE = mgh
Efficiency (%) = useful power output (W) × 100
total power input (W)
Efficiency = Pout
Pin
Efficiency (%) = useful energy output (J) × 100
total energy input (J)
Efficiency = Eout
Ein
Moment (Nm) = force (N) × perpendicular distance from pivot (m)
M = Fd
Sum of clockwise moments (Nm) = sum of anticlockwise moments (Nm)
F1d1 = F2d2
-1
-1
Momentum (kgms ) = mass (kg) × velocity (ms )
p = mv
-1
Force (N) = change in momentum (kgms )
time (s)
F = Δp
t
Impulse (kgms-1 or Ns) = change in momentum (kgms-1)
2
Ft = mv -mu
-1
Centripetal Force (N) = mass (kg) × velocity (ms )
radius (m)
F = mv2
r
Orbital Period (s) = 2 × π × radius (m)
velocity (ms-1)
T = 2πr
v
Thermal
Boyle’s Law for changes in gas pressure at constant temperature :
pressure1 (Pa) × volume1 (m3) = pressure2 (Pa)× volume2 (m3)
or
pressure (Pa) × volume (m3) = constant
P1V1 = P2V2
or
PV = constant
Energy (J) = mass (kg) × specific heat capacity (Jkg-1°C-1) × temperature change (°C)
E = mcΔT
-1
-1
-1
Thermal capacity (J°C ) = mass (kg) × specific heat capacity (Jkg °C )
-1
Energy transferred (J) = mass (kg) × specific latent heat (Jkg )
-1
Expansion (m) = linear expansivity (°C ) × original length (m) × temperature rise (°C)
C = mc
E = ml
Expansion = αlΔT
Electricity
Current (A) = charge (C)
time (s)
I=Q
t
Voltage (V) = energy transferred (J)
charge (C)
V=E
Q
Voltage (V) = current (A) × resistance (Ω)
V = IR
Power (W) = current (A) × voltage (V)
P = IV
2
Power (W) = current (A) × resistance (Ω)
P = I2R
Energy transferred (J) = current (A) × voltage (V) × time (s)
ΔE = IVt
Energy transferred (J) = power (W) × time (s)
ΔE = Pt
Resistors in series: Total Resistance (Ω) = sum of individual resistors (Ω)
RTOTAL = R1+R2+R3+...Rn
Resistors in parallel:
1
total resistance (Ω)
=
1
sum of individual resistors (Ω)
Resistance (Ω) = resistivity (Ωm) × length (m)
area (m2)
Note: since wires have a circular cross section, area = π × radius 2
R = ρl
A
Transformers: voltage in secondary coil (V) = turns on secondary coil
voltage in primary coil (V)
turns on primary coil
Vs = Ns
Vp Np
Transformers: voltage in primary coil (V) = current in secondary coil (A)
voltage in secondary coil (V) current in primary coil (A)
Vp = Is
Vs Ip
Waves
Wave speed (ms-1) = frequency (Hz) × wavelength (m)
c = fλ
Frequency (Hz) = 1
Period (s)
F=1
T
Refractive index = sine of the angle of incidence, i
sine of the angle of refraction, r
n = sini
sinr
Refractive index = speed of light in vacuum
speed of light in material
n = cv
cm
Refractive index =
n= 1
sinc
1‌‌
sine of critical angle
Nuclear
Radioactive alpha decay:
Radioactive beta decay:
Radioactive gamma decay:
Energy (J) = mass defect (kg) × speed of light2 (ms-1)
Compiled by J.Wilson January 2020
E = mc2