PHYSICS Module 2: Waves, sound and light Unit 1: Transverse pulses Pulse: a single disturbance on a medium (spring or rope). Transverse pulses: the particles of the medium move perpendicularly to the direction of propagation of the pulse. Pulse length: the distance from one end of the pulse to another. Disturbance (displacement): direction and distance that the medium has moved from the rest position. Amplitude: the maximum disturbance from its equilibrium position. Unit 2: Superposition of pulses Interference: when 2+ pulses interact with each other at the same time on the same medium. The disturbance increases and after they cross, the pulse carries on unchanged. Superposition: placed on top of each other. Principle of superposition: when pulses cross the combined disturbance at any point is the sum of disturbances - Constructive disturbances: combined disturbance > individual disturbances - Destructive disturbance: combined disturbance < individual disturbance Unit 3: Transverse waves Waves: many pulses ( a succession) of pulses Transverse waves: a succession of transverse pulses Disturbance (displacement): direction and distance that the medium has moved from the rest position. Amplitude: the maximum disturbance from its equilibrium position. Crest: the highest point in a wave (max point) Trough: the lowest point in a wave (min point) Rest position: the position where the medium stop and are in a state of equilibrium Wavelength: distance between 2 crests or 2 troughs (ฦ, lambda) Phase: what a wave motion is doing at a particular time. - In phase: 2 points on a wave that move in a way that they are at similar points. - Out of phase: 2 points on a wave that move in a way that they are at similar points. Unit 4: Wave speed Frequency (f): the number of cycles of a wave per second. Measured in hertz (Hz). 1KHz= 1000Hz 1MHz=1000000 Hz Period (T): the time taken to complete a single cycle of a wave. Measured in seconds (s). F= 1 period and frequency are inversely proportional ๐ Wave speed (v): the distance travelled by a wave (or its crest) in one second. ๐. ๐ 1. v= −1 ๐๐๐ ๐ก๐๐๐๐ ๐ก๐๐๐ฃ๐๐๐๐๐ ๐๐ฆ ๐ ๐๐๐๐ ๐ก ๐๐ ๐กโ๐ ๐ค๐๐ฃ๐ ๐ก๐๐๐ ๐๐๐ก๐๐๐ฃ๐๐ 2. v= fλ Unit 5: Longitudinal waves Longitudinal wave: particles vibrate parallel to the direction of the waves propagation. Compression: where the turns or particles are close together. Compress means squeeze together. Rarefaction: where the turns or particles are further apart. (rarefy means to make it less dense). Wavelength: distance between 2 compressions or rarefactions. For other types of waves, it is the distance between 2 successive points in phase. Amplitude: maximum disturbance of a particle from its rest position. Unit 6: Longitudinal waves and sound Sound waves: longitudinal waves caused by vibration that produce regular variation in pressure. Unit 7: Sound Phenomena Sound waves pass from particle to particle. It is the slowest in gas because the particles are far apart and intermolecular forces are weak. It is faster in liquid and the fastest in solids Pitch: how high/low the sound is- depends on the frequency. The higher the frequency the lower the pitch and vice versa. Loudness: related to: - Amplitude: larger the amplitude, louder the sound. - Sensitivity of the human ear: eg, a soprano sounds louder than bass even though their voices have the same power. Tone: the distinctive sound of a musical instrument. Unit 8: Ultrasound and beyond human perception Ultrasound: frequencies higher than the range of human hearing. Ultrasound image: the high frequency gives the ultrasound a short wavelength which allows it to reflect off small objects (like a water ripple with a short wavelength). Ultrasound scans do this and transmit the waves into the next medium. A computer then uses the reflected waves to construct an image. It is less damaging than X-rays Ultrasound treatments: -Helps reduce swelling - Transmits energy to break up kidney stones Earthquake prediction: before the rocks underneath the surface move, they create vibrations which only animals can hear which causes them to behave unusually. Unit 9: The nature of electromagnetic radiation Electromagnetic radiation: types of radiation that have similar properties e.g. radio waves, light and X-rays. Because we cannot see them, we use scientific models to understand them better: - Wave model: shows how the retina bends light so it forms an image. - Particle model: shows how light transfers energy to the cells in the retina. - Wave-particle duality: some aspects of EM radiation are best explained with the particle model and some with the wave model. This is the dual nature of EM radiation. Accelerating electric charge: the source of EM radiation. Electromagnetic wave: A moving electric charge has a magnetic field around it. If it accelerates, the electric and magnetic fields are disturbed. The fields then oscillate and produce electromagnetic radiation. Electric charge: property of particles that gives rise to electrical phenomena. Magnetic field: region where a magnetic/ferromagnetic material experiences a force. Electric field: region where an electric charge experiences a force. Propagation of electromagnetic waves: - Electric and magnetic fields oscillate perpendicularly with a transverse wave motion. - Because they are mutually regenerating fields, they do not need a medium with particles for propagation. Unit 10: Electromagnetic Spectrum All the frequencies of electromagnetic radiation arranged in order. Electromagnetic waves obey the wave speed relationship: ๐ = ๐λ 8 −1 c= speed of light in a vacuum, 3 x10 ๐. ๐ f= frequency λ = wavelength Penetrating ability: high frequencies can penetrate the skin and sometimes body. Higher frequencies of ultraviolet can damage the skin and eyes. Exposure to X-rays must be limited. Uses: EM radiation: Characteristics and uses Radio waves Lowest frequency; longest wavelength. TV waves High frequency radio waves. Microwaves Used in microwave ovens to transfer energy to Infrared Transfer heat. Used to detect objects/people in the absence of visible light. Visible light Our sense of sight detects visible light. Ultraviolet (UV) SA bank notes ink absorbs energy of UV light and re-emits as visible light X-rays Used to produce images of organs and bones. Gamma rays Very high energy used in medical sterilisation. (fluorescence). Used to detect fraud. Unit 11: Photons Quantisation: the quantity comes in amounts that cannot be made smaller. Quantum: an indivisible amount of a physical quantity. The photon: a quantum of electromagnetic radiation that has zero mass and travels at the speed of light. Planck’s constant: A photon’s energy increases with its frequency (proportional). Eαf E=hf E= energy of photon (joules J) f= frequency of photon (Hz) −34 h= Planck's constant. 6.63 x 10 J.s Module 5: Electricity and magnetism Unit 2: Electrostatics Electric charges: Electrostatics (static electricity) is the interaction of stationary charges Positive/negative charges: Atoms without charge have a net charge (protons +neutrons) of zero. The positive charge has more protons than electrons and vice versa. Charging by contact: Some objects transfer electrons even faster when rubbed (triboelectric charging). When 2 substances rub, one loses electrons, and one gains electrons so they are unlike and attract. Forces charges exert on each other: Like charges repel and unlike attract. Charged objects attract uncharged objects. Polarisation: When a paper and balloon rub, the charges closest to the balloon are more positive than the other side. This means the paper is polarised because it has an uneven distribution of charge. Unit 3: Conservation and quantisation of charge Charge is measured in Q (Coulomb) Principle of conservation of charge: the net charge of an isolated (no charge can exit/enter) system remains constant during a physical process. Sphere: They rest on insulated stands. When the touch the energy is added (Qnet) 1 microcoulomb: μm= 1 x 10(-6) 1 nanocoulomb: nm 1 x 10(-9) Q (charge) = n (integer) x qe (1,6 x 10 (-19)) Principle of quantisation of charge: every charge is an integer multiple of the electron charge. Unit 4: Electric circuits An electric circuit: a continuous conducting path in which electricity flows. Consists of: - Energy source: a source containing chemical potential energy which supplies the rest of the circuit - Connecting wires: are made of a conducting metal in which little energy is lost - Resistance: it opposes the flow and transfers electricity out of the circuit. Additional components: - A switch: controls the flow of current - Insulators: insulators prevent short circuits It follows the principle of conservation of charge as it remains the same throughout the circuit - Series: components are connected in a way that there is a single path for current. Switches control the entire circuit. - Parallel: components are connected in a may that there are 1+ paths for current. Switches control only a single part. Unit 5: Emf and potential difference Why charges flow: Electricity flows to where the potential energy is less and as they do they transfer energy. Potential difference (voltage): “energy per coulomb” or the energy 1Q loses/gains when passing through a battery/resistor. It is the change in electrical potential energy per unit charge between 2 points. (the voltage between 2 points. V= potential difference (Volts) W= energy transfer (Joules) Q= charge (Coulombs) The voltmeter: always connect in parallel. Connect the negative of the battery to the terminal and the positive to the largest range. The voltmeter uses current so small it does n0t affect the circuit. Emf: the voltage measured when no current is flowing (there is no resistor) Terminal potential difference: the voltage measured when the current is flowing (there is a resistor). It is less than emf. Unit 6: Current The rate (how much per second) of the flow of charge I= electric current (ampere) Q= charge (coulombs โณt= time taken (seconds) The ammeter: Connect in series. Negative ammeter to the negative battery. Positive battery to the largest range. Never connect in parallel- high current causes damage. Current direction: From the positive terminal to the negative. Sometimes called conventional current direction. Why a battery goes flat: when all the current has been transferred. A high current circuit uses energy faster than a low current one. Unit 7: Resistance The opposition to the flow of current. Factors: material type, size of resistance material, the temperature of the resistor. Transfer of energy: when charges move through resistance, they collide with its particles and transfer kinetic energy causing vibration. This causes heat. Measuring resistance: resistance is the ratio of potential difference to current(V: I). It is measured in ohms โฆ. Resistance increases while current decreases, so they are inversely proportional. Unit 8: Resistors in series Current in series: Remains the same unless more resistors are added (will reduce) Voltage: the sum of all the volts. Resistors that divide the voltage are called voltage dividers. Vs= Vโ+ Vโ + Vโ Resistors: equivalent resistance in series is Rโ + Rโ + Rโ Unit 9: Resistors in parallel Current and voltage: -Voltage in parallel is equal - Sum of current through resistor= total current - Resistors in parallel are called current dividers because Ip=Iโ+Iโ - In parallel, more pathways for current are opened. The resistance decreases and the current increases. Resistors: V/Rp = V/Rโ + V/Rโ . Remove common factor Module 7: Mechanics Unit 1: Vectors and Scalars Physical quantities: a measurable quantity of something found in nature. Types: - Scalars: Physical quantities consisting of size only. Can be added/subtracted like ordinary numbers. Negative scalars often represent less eg 10C and -10C - Vectors: Physical quantities with both magnitude and direction. Negative and positive vectors have the same value but opposite directions. Right and up is positive. Down and left is negative. Vector diagram: Properties of vectors: -They are only equal if they have the same magnitude and direction - Only vectors of the same kind can be added, no scalars. - Multiplication by a scalar changes the magnitude of the vector Resultant: has the same effect of 2+ vector quantities Unit 2: Position Motion: change in position of a body with respect to time Frames of reference: reference points (eg axes) that show the definition of an object’s position. A position is plotted relative to the reference point. One dimensional motion: is along a straight line in a direction (vector). On the Cartesian plane, x is horizontal and y is vertical. Unit 3: Distance and displacement Distance: the length of a path on which an object moves to position (scalar; metres). Formula: final position + initial position Displacement: magnitude and direction of a straight line from its initial to the final position (vector; ๐ซx). Formula: ๐ซx= xf -xi Unit 4: Speed and Velocity Average speed: distance/ time= m.s๏นฃ¹ (scalar) Average velocity: displacement/ time= โฝ (vector) Average time: ๐ซt= 1/f (frequency; Hz) Converting units: (km.hr-1) ÷ 3.6= (m.s-1) Unit 5: Average acceleration Acceleration = velocity/ time= m.s-2 (vector). It means speed is increasing. Deceleration means decreasing speed. We could determine whether it is +/- (direction) by: - The positive direction of the frame of reference - The change in velocity. Acceleration of a trolley on a slope: -When speeding up ฤ and โฝ are in the same direction and have the same magnitude/ sign. - When slowing down the direction, magnitude, and sign change. โฝ is decreasing. - Acceleration needs velocity to show direction. Unit 6: Instantaneous velocity and speed Uniform: constant in the course of time. ๐ฃ๐๐๐ก๐๐๐๐ ๐โ๐๐๐๐ Gradient: the slope of a graph. โ๐๐๐๐ง๐๐๐ก๐๐ ๐โ๐๐๐๐ ๐๐๐ ๐๐๐๐๐๐๐๐๐ก Instantaneous velocity: ๐๐๐๐๐๐๐ก๐๐ ๐๐๐๐ ๐ก๐๐๐ ; vector; is the gradient of the tangent (the line that touches the curve at a single point) Instantaneous speed: of the same magnitude as instantaneous velocity; scalar. Unit 7: Investigate uniform acceleration The acceleration at a particular moment Unit 8-9: Graphs of motion See textbook for examples. Unit 10: Equations of motion Kinematic equations of motion: used instead of drawing graphs. Conditions: - Acceleration must be uniform - Motion must be in 1D (straight line motion) Δ๐ฅ = ๐ฃ0โ๐ก + 21โ๐๐ก2 ๐ฃ = ๐ฃ0โ + ๐๐ก Δ๐ฅ = (๐ฃ+๐ฃ0โโ )๐ก 2 Δ๐ฅ = ๐ฃ0โ๐ก + 2 1โ ๐๐ก 2 Unit 11: Equations of motion and road safety Braking distance: the shortest distance it takes for a vehicle’s brakes to bring it to a stop. Average ๐= -6๐. ๐ −2 Reaction time: more or less 0.75s, even more when under the influence of drugs/alcohol. Thinking distance: 1.5s Stopping distance: braking distance + thinking distance Unit 12: Different kinds of energy Potential energy: energy an object has because of its position, state or shape. Types: electrical, chemical, and radiated potential energy Gravity: a force of attraction that bodies possess because of their mass. gravitational field: region where an object experiences a force of gravity. Gravitational potential energy: the energy an object has because of its position in a gravitational field relative to a reference point. (Ep) Ep(joules) = m(kg) X g(9.8m.s2) X h (m) Kinetic energy: energy an object has because of its motion. Energy is a scalar quantity. Unit 13: Conservation of energy Law of conservation of energy: energy is never created or destroyed but only transferred from one form to another. Mechanical energy Em: the sum of kinetic and gravitational potential energy of an object. Principle of conservation of mechanical energy: in the absence of air resistance and friction the mechanical energy of an object in earth's gravitational field is constant (conserved ) When the mechanical energy is conserved M1= M2 - mechanical energy is conserved as long as no energy is transferred out of the system. - relevant variables = velocity and height - the path a body takes can be ignored. F O R M U L A S: Qnet= Qโ +Qโ + Qโ Energy of each sphere (Q)= Qnet ÷ 2 Q=nqe V=W÷Q I= Q÷โณt V=IR I=V÷R R= V÷I Series: Equivalent resistance: Rs= Rโ + Rโ + Rโ Total voltage: Vs= Vโ+ Vโ + Vโ Parallel: Total current: Ip=Iโ+Iโ Equivalent resistance: 1/Rp= 1/Rโ + 1/Rโ Resultant: FR= Fโ+Fโ Displacement: ๐ซx= xf -xi Distance: final position+ initial position Average speed: D/t= m.s๏นฃ¹ Average velocity:๐ซx/๐ซt = โฝ Average acceleration: ฤ=โฝ/๐ซt= m.s -2
