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Physics flashcards

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Topic 1: Energy

What is a system, in energy questions?: An object or group of objects. When a system changes, energy is stored differently before and after the change, but the total amount is conserved.
Three ways the energy of a system can be changed: Heating, work done by a force, and work done when a current flows.
Kinetic energy equation, with units: Ek = ½mv² Ek in J, m in kg, v in m/s.
A moving object doubles its speed. What happens to its kinetic energy?: It quadruples (× 4), because Ek depends on v².
Elastic potential energy equation, and the condition for using it: Ee = ½ke² (k spring constant in N/m, e extension in m). It applies only within the limit of proportionality.
Gravitational potential energy equation, with units: Ep = mgh Ep in J, m in kg, g in N/kg, h (height gained) in m.
Specific heat capacity: definition and equation: The energy needed to raise the temperature of 1 kg of a substance by 1 °C. ΔE = mcΔθ (J, kg, J/kg °C, °C).
Required practical 1: what is measured, and the main source of error?: The specific heat capacity of a material: an electric heater supplies a measured amount of energy and the temperature rise is recorded. Some energy is always dissipated to the surroundings, so insulate the block.
Power: definition and two equations: Power is the rate of energy transfer (or the rate of doing work). P = E/t and P = W/t. 1 W = 1 J/s.
A 0.20 kg ball is thrown up at 8.0 m/s. What is its kinetic energy at launch?: Ek = ½ × 0.20 × 8.0² = 6.4 J
Principle of conservation of energy: Energy cannot be created or destroyed, only transferred usefully, stored or dissipated.
Name the eight energy stores: Kinetic, gravitational potential, elastic potential, chemical, thermal, magnetic, electrostatic and nuclear.
Four ways energy is transferred between stores: Mechanically (by a force), electrically (by a current), by heating, and by radiation (light and sound).
What happens to “wasted” energy?: It is dissipated, usually to the thermal store of the surroundings, where it is spread out and hard to use. It is not destroyed.
Efficiency equations: efficiency = useful output energy transfer ÷ total input energy transfer efficiency = useful power output ÷ total power input No unit; × 100 for a percentage. It can never exceed 1 (100%).
Lubrication: Reduces friction between moving surfaces, so less energy is dissipated.
Thermal insulation: Reduces the rate of energy transfer by conduction.
Two properties of a wall that decide how fast a house loses energy: Its thickness (thicker → slower transfer) and the thermal conductivity of the material (lower → slower transfer).
How can the efficiency of an intended energy transfer be increased?Higher: Reduce wasted transfers: reduce friction (for example by lubrication) and reduce unwanted heating (for example by thermal insulation).
Renewable energy resource: One that is being (or can be) replenished as it is used.
Non-renewable energy resource: One that is not replenished as it is used. Supplies are finite, so it will eventually run out.
Which of the main energy resources are non-renewable?: Fossil fuels (coal, oil and gas) and nuclear fuel. Bio-fuel, wind, hydro-electricity, geothermal, the tides, the Sun and water waves are renewable.
Is renewable the same as reliable? Give an example.: No. Wind is renewable but unreliable (no output on still days). Coal is reliable but non-renewable.
Tidal power vs wave power: which is predictable, and why?: Tidal: tides happen at known times each day. Waves depend on the weather, so wave power is unreliable.
Environmental impacts of burning fossil fuels: Carbon dioxide is released, which contributes to global warming and climate change. Coal and oil also release sulfur dioxide, which causes acid rain.
Environmental impact of nuclear power: No carbon dioxide while running, but it produces radioactive waste that must be stored safely for a very long time, and there is a risk of a serious accident.
Science can identify an energy problem but not always solve it. Name the kinds of barrier.: Political, social, ethical and economic considerations (for example cost, energy security, local objections, lost jobs).

Topic 2: Electricity

Electric current: definition and equation: The rate of flow of electrical charge. Q = It (Q in C, I in A, t in s).
Equation linking potential difference, current and resistance: V = IR (V in volts, I in amperes, R in ohms).
Ohmic conductor: A conductor in which current is directly proportional to potential difference at constant temperature, so its resistance is constant.
I–V graph of a filament lamp, and why it has that shape: An S-shaped curve that flattens at both ends. As the current rises the filament gets hotter and its resistance increases.
How does a diode behave?: Current flows in one direction only. Its resistance is very high in the reverse direction.
Thermistor vs LDR: Thermistor: resistance falls as temperature rises (used in thermostats). LDR: resistance falls as light intensity rises (used for lights that switch on in the dark).
How do you connect meters to measure the resistance of a component?: Ammeter in series with the component; voltmeter in parallel across it. Then R = V ÷ I.
Required practical 3: how does the resistance of a wire depend on its length?: Resistance is directly proportional to length. Keep the temperature constant (small current, switch off between readings).
A lamp has 3.0 V across it and 0.60 A through it. What is its resistance?: R = 3.0 ÷ 0.60 = 5.0 Ω
Current and potential difference in a series circuit: The current is the same through each component. The supply pd is shared between the components.
Current and potential difference in a parallel circuit: The pd is the same across each branch. The branch currents add up to the total current.
Total resistance of resistors in series: R_total = R₁ + R₂ (adding a resistor in series increases the total resistance).
Why does adding a resistor in parallel decrease the total resistance?: It gives the charge an extra path. The total resistance of two resistors in parallel is less than the smaller one.
A 10 Ω and a 15 Ω resistor are in series with a 5.0 V supply. Find the current.: R_total = 25 Ω, so I = 5.0 ÷ 25 = 0.20 A
In a thermistor and fixed-resistor circuit, what happens to the thermistor’s share of the pd when it gets colder?: Its resistance rises, so it takes a bigger share of the supply pd.
Direct vs alternating potential difference: Direct: one direction only (cells and batteries). Alternating: keeps reversing direction (the mains).
Frequency and potential difference of the UK mains supply: Alternating current at 50 Hz and about 230 V.
Live, neutral and earth wires: colours: Live: brown. Neutral: blue. Earth: green and yellow stripes.
What does each wire do, and what is its pd?: Live: carries the alternating pd, about 230 V. Neutral: completes the circuit, at or close to 0 V. Earth: safety wire at 0 V, carries current only if there is a fault.
Why is a live wire dangerous even when the switch is open?: It is still at about 230 V and your body is at 0 V, so touching it puts a large pd across you and a current flows through you: an electric shock.
What is the danger of a connection between the live wire and earth?: It is a low-resistance path, so a very large current flows, which can cause a fire (or a shock if the path is through a person).
Two equations for electrical power: P = VI P = I²R (P in W, V in V, I in A, R in Ω)
Two equations for energy transferred electrically: E = Pt (J, W, s) E = QV (J, C, V)
What does the energy transferred by an appliance depend on?: Its power and how long it is switched on. Work is done when charge flows; motors transfer energy to kinetic stores, heaters to thermal stores.
A 1.5 kW heater is on for 2 hours. How much energy does it transfer?: E = Pt = 1500 × 7200 = 10 800 000 J (10.8 MJ)
The National Grid: A system of cables and transformers linking power stations to consumers. Step-up transformers raise the pd for transmission; step-down transformers lower it for domestic use.
Why is electricity transmitted at a high potential difference?: For the same power (P = VI), a higher pd means a lower current. A lower current means much less heating of the cables (P = I²R), so less energy is wasted.
How do two insulators become charged when rubbed together?: Electrons are transferred from one to the other. The one that gains electrons becomes negative; the one that loses them becomes equally positive.
Forces between charged objects: Like charges repel; unlike charges attract. Both are non-contact forces.
Electric field: The region around a charged object where another charged object experiences a force.
Electric field lines round an isolated charged sphere: Radial: outward for a positive sphere, inward for a negative one. The field is strongest close to the sphere.
Why does sparking happen?: Charge builds up on an object, so the pd between it and a nearby earthed object becomes large enough for electrons to jump across the gap.
Exam trap: which charged particles move when an object is charged by friction?: Only electrons. Protons and “positive charge” do not move.

Topic 3: Particle model of matter

Density equation, with units: ρ = m / V ρ in kg/m³, m in kg, V in m³.
Why is a gas much less dense than the same substance as a solid or liquid?: The same mass of particles is spread over a much bigger volume, because gas particles are far apart.
Particle arrangement and motion in a solid, a liquid and a gas: Solid: touching, regular, vibrate in place. Liquid: touching, irregular, slide past each other. Gas: far apart, random, move fast in all directions.
Why is a change of state a physical change?: Mass is conserved and, if the change is reversed, the material gets its original properties back. No new substance forms.
Required practical 5: finding the volume of an irregular solid: By displacement: measure the rise in water level in a measuring cylinder, or collect the overflow from a eureka can in a measuring cylinder.
A 0.60 kg block has a volume of 2.4 × 10⁻⁴ m³. What is its density?: ρ = 0.60 ÷ 2.4 × 10⁻⁴ = 2500 kg/m³
Sublimation: A change of state from solid straight to gas.
Internal energy: The total kinetic energy and potential energy of all the particles (atoms and molecules) that make up a system.
Two things heating a system can do: Raise its temperature (particles gain kinetic energy), or change its state (particles gain potential energy, temperature stays constant).
Specific latent heat: The energy needed to change the state of 1 kg of a substance with no change in temperature. E = mL (J, kg, J/kg).
Specific latent heat of fusion vs of vaporisation: Fusion: solid ↔ liquid. Vaporisation: liquid ↔ vapour.
What is happening on a flat section of a heating graph?: A change of state (melting or boiling). The energy supplied raises the internal energy, but the temperature stays constant. Use E = mL, not ΔE = mcΔθ.
How much energy melts 0.50 kg of ice at 0 °C? (L = 334 000 J/kg): E = mL = 0.50 × 334 000 = 167 000 J
What causes gas pressure?: Molecules in constant random motion collide with the container walls, producing a net force at right angles to the wall.
Temperature of a gas is related to…: The average kinetic energy of its molecules.
Why does the pressure of a gas rise when it is heated at constant volume?: The molecules move faster, so they hit the walls more often and with more force.
Why does the pressure of a gas fall when its volume increases at constant temperature?: The molecules move at the same speed but hit each unit area of the wall less often.
Gas at 200 kPa in 0.050 m³ is compressed to 0.020 m³ at constant temperature. New pressure?: p₁V₁ = p₂V₂, so p₂ = 200 × 0.050 ÷ 0.020 = 500 kPa
Why does a bicycle pump get warm when you use it?Higher: Work is done on the gas (work is the transfer of energy by a force). This increases the internal energy of the gas, so its temperature rises.

Topic 4: Atomic structure

Size of an atom and of its nucleus: Atom radius: about 1 × 10⁻¹⁰ m. Nucleus radius: less than 1/10 000 of the radius of the atom.
Atomic number vs mass number: Atomic number: protons only. Mass number: protons + neutrons.
Isotope vs ion: Isotopes of an element have different numbers of neutrons. An ion has a different number of electrons from protons (so it is charged).
How many protons, neutrons and electrons are in an atom of sodium-23 (atomic number 11)?: 11 protons, 23 − 11 = 12 neutrons, 11 electrons.
What happens to an electron when an atom absorbs or emits electromagnetic radiation?: Absorbs: the electron moves to a higher energy level (further from the nucleus). Emits: it moves to a lower energy level (closer to the nucleus).
Plum pudding model vs nuclear model: Plum pudding: a ball of positive charge with electrons embedded in it. Nuclear: mass and positive charge concentrated in a tiny nucleus, with electrons outside.
Alpha scattering: what each observation showed: Most went straight through: the atom is mostly empty space. Some were deflected: the centre is charged. Very few bounced back: the centre is tiny and holds most of the mass.
Who gave evidence for the neutron, and when, relative to the nuclear model?: James Chadwick, about 20 years after the nucleus became an accepted idea.
Alpha, beta and gamma: what each is: Alpha: 2 protons + 2 neutrons (a helium nucleus). Beta: a high-speed electron ejected from the nucleus as a neutron turns into a proton. Gamma: electromagnetic radiation from the nucleus.
Penetration and ionising power of alpha, beta and gamma: Alpha: stopped by paper, a few cm in air, most ionising. Beta: stopped by thin aluminium. Gamma: reduced by thick lead or concrete, least ionising.
Activity: The number of decays per second of a source, in becquerel (Bq).
Count-rate: The number of decays recorded each second by a detector (for example a Geiger-Muller tube).
Effect of alpha and of beta decay on mass number and atomic number: Alpha: mass number − 4, atomic number − 2. Beta: mass number unchanged, atomic number + 1. Gamma: no change to either.
Half-life: The time it takes for the number of nuclei of the isotope in a sample to halve, or for the count-rate (or activity) to fall to half its initial level.
A source has activity 800 Bq and half-life 2 days. What is its activity after 6 days?: 6 ÷ 2 = 3 half-lives: 800 → 400 → 200 → 100 Bq
Net decline as a ratio after n half-livesHigher: 1 : 2ⁿ. For example, after 4 half-lives it is 1 : 16.
Contamination vs irradiation: Contamination: radioactive atoms get on or into an object, so the hazard continues. Irradiation: the object is exposed to radiation from outside; it does not become radioactive.
Sources of background radiation: Natural: rocks and cosmic rays from space. Man-made: fallout from nuclear weapons testing and nuclear accidents.
Unit of radiation dose: The sievert (Sv). 1000 millisieverts (mSv) = 1 Sv.
Hazard of a source with a short half-life vs a long half-life: Short: very active at first but the activity falls quickly. Long: less intense, but stays hazardous for a long time.
What kind of source is chosen as a medical tracer, and why?: A gamma emitter, so the radiation can leave the body and reach the detector, with a half-life of hours: long enough to do the job, short enough to limit the dose.
Why is a beta source used to monitor the thickness of thin card?: Alpha would be stopped by the card; gamma would pass through almost unchanged, so small changes in thickness would not show.
Nuclear fission: A large unstable nucleus (such as uranium or plutonium) absorbs a neutron and splits into two smaller nuclei of roughly equal size, releasing two or three neutrons, gamma rays and energy.
Chain reaction: The neutrons released by one fission go on to cause further fissions. It is controlled in a nuclear reactor and uncontrolled in a nuclear weapon.
Nuclear fusion: Two light nuclei join to form a heavier nucleus. Some of the mass may be converted into the energy of radiation.
What usually has to happen before a uranium-235 nucleus undergoes fission?: It must absorb a neutron. Spontaneous fission is rare.
Fission vs fusion: Fission: a heavy nucleus splits. Fusion: light nuclei join.

Topic 5: Forces

Scalar vs vector: Scalar: magnitude only. Vector: magnitude and direction, shown by an arrow whose length represents the size.
Contact forces: examples: Friction, air resistance, tension and normal contact force.
Non-contact forces: examples: Gravitational, electrostatic and magnetic forces.
Weight equation, and where weight acts: W = mg (W in N, m in kg, g in N/kg). Weight acts at the object’s centre of mass and is measured with a newtonmeter.
Mass vs weight: Mass: in kg, the same everywhere. Weight: a force in N, which depends on the gravitational field strength.
Find the resultant of 45 N to the right and 60 N to the left.: 60 − 45 = 15 N to the left
Resolving forces and scale diagramsHigher: A single force can be resolved into two components at right angles. If an object is in equilibrium, the force arrows drawn tip-to-tail make a closed triangle.
Work done equation, with units: W = Fs W in J, F in N, s (distance moved along the line of action of the force) in m.
How many newton-metres is one joule?: 1 J = 1 N m: one joule of work is done when a force of one newton causes a displacement of one metre.
What happens when work is done against friction?: Energy is transferred to the thermal store, so the temperature of the object rises.
A 25 N force moves an object 4.0 m along its line of action. Work done?: W = 25 × 4.0 = 100 J
Why does stretching, bending or compressing an object need more than one force?: With only one force acting, the object would simply accelerate instead of changing shape.
Elastic vs inelastic deformation: Elastic: the object returns to its original shape when the forces are removed. Inelastic: it does not.
Force–extension equation, and when it applies: F = ke (F in N, k in N/m, e in m). It applies up to the limit of proportionality, where extension is directly proportional to force.
Required practical 6: how do you find a spring constant from the results?: Extension = stretched length − original length (in m). In the linear region, k = F ÷ e, or the gradient of the force–extension graph.
A spring (k = 25 N/m) is stretched 0.20 m. Force and energy stored?: F = 25 × 0.20 = 5.0 N Ee = ½ × 25 × 0.20² = 0.50 J
Work done stretching a spring: Equals the elastic potential energy stored, provided the spring is not inelastically deformed.
Moment of a force: equation: M = Fd M in N m, F in N, d = perpendicular distance from the pivot to the line of action of the force, in m.
Condition for a balanced object (principle of moments): Total clockwise moment about a pivot = total anticlockwise moment about that pivot.
Calculate the moment of a 30 N force acting 0.40 m from a pivot.: M = 30 × 0.40 = 12 N m
What do levers and gears do?: They transmit the rotational effects of forces. A small gear driving a larger gear gives a bigger moment, but the larger gear turns more slowly.
Pressure at a surface: equation and units: p = F / A p in Pa, F (force normal to the surface) in N, A in m².
In which direction does the pressure in a fluid act on a surface?: At right angles (normal) to the surface.
Why does atmospheric pressure decrease with height?: The atmosphere gets less dense with height, and there is less air above a surface, so the weight of air above it is smaller.
Pressure due to a column of liquidHigher: p = hρg (h height of the column in m, ρ density in kg/m³, g in N/kg). Pressure increases with depth and with the density of the liquid.
Pressure due to 5.0 m of water? (ρ = 1000 kg/m³, g = 9.8 N/kg)Higher: p = 5.0 × 1000 × 9.8 = 49 000 Pa
What causes upthrust, and when does an object float?Higher: The pressure on the bottom surface is greater than on the top, giving a resultant upward force. An object floats if the upthrust equals its weight before it is fully submerged (its density is less than the fluid’s).
Distance vs displacement; speed vs velocity: Distance and speed are scalars. Displacement and velocity are vectors: they include a direction.
Typical speeds: walking, running, cycling, sound in air: Walking ~1.5 m/s, running ~3 m/s, cycling ~6 m/s, sound in air ~330 m/s.
Acceleration equation, and the equation-sheet equation without time: a = Δv / t (m/s²) v² − u² = 2as
A car accelerates from rest at 2.5 m/s² over 80 m. Final velocity?: v² = 0 + 2 × 2.5 × 80 = 400, so v = 20 m/s
What does the gradient of a distance–time graph and of a velocity–time graph give?: Distance–time: speed. Velocity–time: acceleration.
What does the area under a velocity–time graph give?Higher: The distance travelled (displacement).
Terminal velocity: The steady velocity reached when the resistive force (drag) equals the weight, so the resultant force is zero.
Newton’s first law: If the resultant force on an object is zero, its velocity does not change: it stays at rest or keeps moving at the same speed in the same direction.
Newton’s second law: Acceleration is proportional to the resultant force and inversely proportional to mass: F = ma.
Newton’s third law pair vs balanced forces: A third-law pair acts on two different objects and is the same type of force. Balanced forces act on one object.
Inertia and inertial massHigher: Inertia: the tendency of an object to stay at rest or in uniform motion. Inertial mass = force ÷ acceleration: a measure of how hard it is to change its velocity.
Stopping distance: Stopping distance = thinking distance + braking distance. Typical reaction times are 0.2–0.9 s.
Thinking vs braking distance: what affects each?: Thinking: the driver’s reaction time (tiredness, drugs, alcohol, distractions) and speed. Braking: speed, wet or icy roads, worn brakes or tyres.
Speed doubles (same reaction time and deceleration). Effect on thinking and braking distance?: Thinking distance doubles; braking distance quadruples.
Why does an object moving in a circle at constant speed have a changing velocity?Higher: Its direction is always changing, and velocity is a vector, so the velocity changes (it is accelerating).
Momentum equation, with unitsHigher: p = mv p in kg m/s, m in kg, v in m/s.
Conservation of momentumHigher: In a closed system, the total momentum before an event is equal to the total momentum after it.
Calculate the momentum of a 0.060 kg ball at 25 m/s.Higher: p = 0.060 × 25 = 1.5 kg m/s
A 2.0 kg trolley at 3.0 m/s hits a stationary 1.0 kg trolley and they move off together. Their velocity?Higher: Momentum before = 2.0 × 3.0 = 6.0 kg m/s. After: 3.0 kg × v = 6.0, so v = 2.0 m/s.
Force and change in momentumHigher: F = mΔv / Δt: force equals the rate of change of momentum.
How do air bags, seat belts and crash mats reduce injury?Higher: They increase the time taken for the change in momentum, so the rate of change of momentum, and so the force, is smaller.

Topic 6: Waves

Transverse vs longitudinal waves: Transverse: oscillations perpendicular to the direction of energy transfer (ripples, EM waves). Longitudinal: oscillations parallel to it, with compressions and rarefactions (sound in air).
Amplitude vs wave height: Amplitude is the maximum displacement from the undisturbed position: half the crest-to-trough height.
Wavelength and frequency: Wavelength: distance from a point on one wave to the equivalent point on the next wave. Frequency: number of waves passing a point each second, in Hz.
Wave speed equation, and period equation: v = fλ (m/s, Hz, m) T = 1/f (T in s)
Evidence that a wave moves but the medium does not travel with it: A floating object bobs up and down on ripples but stays in place; air particles vibrate about fixed positions as sound passes.
A wave has speed 12 m/s and frequency 4.0 Hz. Find its wavelength.: λ = v / f = 12 / 4.0 = 3.0 m
Specular vs diffuse reflection: Specular: from a smooth surface, in a single direction. Diffuse: from a rough surface, scattered in many directions.
Range of normal human hearingHigher: 20 Hz to 20 kHz.
UltrasoundHigher: Sound above 20 kHz. It is partly reflected at boundaries between media, and the echo time gives the distance. Used for medical and industrial imaging.
P-waves vs S-wavesHigher: P-waves: longitudinal, travel through solids and liquids. S-waves: transverse, cannot pass through liquids, so the S-wave shadow shows part of the Earth’s core is liquid.
A sonar pulse (1500 m/s) returns after 0.20 s. How deep is the water?Higher: 1500 × 0.20 = 300 m there and back, so the depth is 150 m.
Order of the electromagnetic spectrum, long wavelength to short: Radio, microwave, infrared, visible, ultraviolet, X-ray, gamma.
Properties shared by all electromagnetic waves: Transverse; all travel at the same speed in a vacuum (or air); transfer energy from source to absorber; form a continuous spectrum.
One use each: radio, microwaves, infrared, visible light: Radio: television and radio. Microwaves: satellite communications, cooking. Infrared: electric heaters, infrared cameras. Visible: fibre optic communications.
Hazards of ultraviolet, X-rays and gamma rays: Ultraviolet: premature skin ageing and increased risk of skin cancer. X-rays and gamma: ionising radiation that can cause gene mutation and cancer.
A radio wave has frequency 200 MHz. What is its wavelength? (c = 3.0 × 10⁸ m/s): λ = 3.0 × 10⁸ ÷ 2.0 × 10⁸ = 1.5 m
What causes refraction, and how does a wave front diagram show it?Higher: A change in wave speed. The part of the wave front that enters the slower medium first slows first, so the wave front turns and the fronts get closer together.
How are radio waves produced and detected?Higher: Oscillations in electrical circuits produce them. When absorbed, they can induce an alternating current with the same frequency as the radio wave.
Convex vs concave lens: Convex: parallel rays converge at the principal focus; image can be real or virtual. Concave: parallel rays spread out as if from the principal focus; image always virtual.
Magnification equation: magnification = image height ÷ object height. It is a ratio, so it has no units (use the same units for both heights).
What colour does a blue object appear in red light?: Black. It reflects only blue light, and there is no blue in red light, so all the light is absorbed.
Required practical 10: how do you compare infrared emission from different surfaces?: Fill a Leslie cube with hot water and hold an infrared detector at the same distance from each face. Matt black emits most; shiny silver emits least.
Which objects emit and absorb infrared radiation?: All bodies, at any temperature. The hotter the body, the more infrared radiation it emits in a given time.
Perfect black body: An object that absorbs all the radiation incident on it, reflecting and transmitting none. It is also the best possible emitter.
What does the temperature of a body change about the radiation it emits?: Both the intensity and the wavelength distribution of the emitted radiation depend on the temperature.
A body stays at a constant temperature. What is true about its radiation?Higher: It absorbs radiation at the same rate as it emits radiation.
A body absorbs radiation faster than it emits it. What happens?Higher: Its temperature increases.
What does the temperature of the Earth depend on?Higher: The rates at which light and infrared radiation are absorbed and emitted by the Earth and its atmosphere, and the radiation reflected back into space.

Topic 7: Magnetism and electromagnetism

Magnetic pole: The place on a magnet where the magnetic forces are strongest.
Permanent vs induced magnet: Permanent: produces its own magnetic field all the time; can attract or repel. Induced: becomes a magnet only when placed in a magnetic field, loses most or all of it quickly when removed, and always attracts.
Magnetic field, and the direction of field lines: The region around a magnet where a force acts on another magnet or a magnetic material. Field lines point from the north pole to the south pole.
The four magnetic materials: Iron, steel, cobalt and nickel.
What evidence does a compass give about the Earth’s core?: A compass needle lines up with a magnetic field wherever it is, which shows the Earth has a magnetic field, produced by its magnetic core.
Where is a magnet’s field strongest, and how do field lines show it?: At the poles. The closer together the field lines, the stronger the field.
Magnetic field around a straight current-carrying wire: Concentric circles around the wire. Stronger with a larger current; weaker further from the wire. Direction from the right-hand grip rule.
Field of a solenoid, and how to make it stronger: Strong and uniform inside, shaped like a bar magnet’s outside. Adding an iron core makes it stronger: this is an electromagnet.
Motor effectHigher: A conductor carrying a current in a magnetic field and the magnet producing the field exert a force on each other.
Fleming’s left-hand ruleHigher: First finger = Field; seCond finger = Current; thuMb = Motion (force). Used to find the direction of the force on a wire.
Force on a wire in a magnetic field: equationHigher: F = BIl (F in N, B magnetic flux density in T, I in A, l length in the field in m), for a wire at right angles to the field. The force is zero if the wire is parallel to the field.
A 0.30 m wire carries 2.5 A at right angles to a 0.40 T field. Force?Higher: F = 0.40 × 2.5 × 0.30 = 0.30 N
How does an electric motor keep turning?Higher: Current flows in opposite directions in the two sides of the coil, so the forces on them are in opposite directions and the coil rotates. A split-ring commutator keeps it turning one way.
How does a loudspeaker work?Higher: Alternating current in a coil in a permanent magnet’s field produces a force that reverses as the current reverses, so the cone vibrates and makes pressure variations: sound.
Generator effectHigher: A potential difference is induced across a conductor that moves relative to a magnetic field, or that is in a changing field. In a complete circuit it drives an induced current.
Direction of the field from an induced currentHigher: It opposes the change that induced it.
Three ways to increase the potential difference induced by moving a magnet in a coilHigher: Move it faster, use a stronger magnet, use more turns on the coil.
Alternator vs dynamoHigher: Alternator: slip rings, gives ac (the output graph crosses the axis). Dynamo: split-ring commutator, gives dc (the graph stays on one side).
MicrophoneHigher: Sound moves a diaphragm and coil in a magnet’s field, inducing a pd, so the current varies like the sound (generator effect).
How does a transformer work?Higher: Alternating current in the primary coil makes a changing magnetic field in the iron core. This changing field passes through the secondary coil and induces an alternating pd across it.
Transformer equationsHigher: Vp / Vs = np / ns Vs × Is = Vp × Ip (for a 100% efficient transformer).
A transformer has 200 primary and 50 secondary turns; Vp = 240 V. Find Vs.Higher: Vs = 240 × 50 ÷ 200 = 60 V. Fewer secondary turns, so it is a step-down transformer.
Why is the core of a transformer made of iron?Higher: Iron is easily magnetised.

Topic 8: Space physics

What is in our solar system?: One star (the Sun), eight planets, dwarf planets, and natural satellites (moons) that orbit planets. It is a small part of the Milky Way galaxy.
How did the Sun form and start to shine?: Gravity pulled a cloud of dust and gas (a nebula) together. It became hot and dense enough for nuclear fusion of light nuclei, which releases energy.
Why is a main sequence star stable?: The inward pull of gravity is balanced by the outward pressure from the energy released by fusion, so the star is in equilibrium.
Life cycle of a star about the size of the Sun: Nebula → protostar → main sequence star → red giant → white dwarf → black dwarf.
Life cycle of a star much more massive than the Sun: Nebula → protostar → main sequence star → red super giant → supernova → neutron star or black hole.
Where are elements heavier than iron produced?: In a supernova, which also distributes the elements throughout the universe. Fusion in stars makes elements up to iron.
What keeps planets and satellites in their orbits?: Gravity, which provides the force towards the centre of the orbit.
A satellite in a stable orbit changes speed. What must happen to its orbit?Higher: The radius must change: a faster speed needs a smaller orbit; a slower speed, a larger one.
Why is a body in a circular orbit accelerating, though its speed is constant?Higher: Its direction changes all the time, so its velocity changes. The resultant force (gravity) acts towards the centre.
Red-shift: The observed increase in the wavelength of light from most distant galaxies.
What pattern does red-shift show?: The further away a galaxy is, the faster it is moving away from us and the bigger its red-shift.
How does red-shift support the Big Bang theory?: Distant galaxies are moving away, faster the further they are, so the universe is expanding. Traced back, it must have begun from a very small region that was extremely hot and dense.
What have observations of supernovae since 1998 suggested?: Distant galaxies are receding ever faster: the expansion of the universe is accelerating.
Name two things about the universe that are still not understood.: Dark mass (dark matter) and dark energy.
A line at 500 nm in the lab is seen at 515 nm from a galaxy. Percentage increase in wavelength?: 15 ÷ 500 × 100 = 3.0%

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Written for AQA GCSE Physics (8463), syllabus 8463 (For first teaching 2016). 42 cards cover Higher tier content only; Foundation students can hide them with “Foundation only”.

Cards by Marlbridge Academic Team; 33 restate definitions from the 8463 revision notes. This deck was reviewed by Iftikhar Azeemi on 2026-11-05. Report an error.

All 8463 notes, practice and topics