The Physics Question Bank

1. Measure the mass of the block using a balance.
2. Put the heater in one hole and a thermometer in the other, with a few drops of water to improve contact.
3. Wrap the block in insulation to reduce energy transfer to the surroundings.
4. Connect the heater to a joulemeter and power supply. Record the starting temperature.
5. Switch on and record the temperature and the energy transferred every minute for 10 minutes.
6. Calculate c using ΔE = mcΔθ (or plot temperature against energy: c = 1 ÷ (m × gradient)).

Top-level tip: say how each quantity in the equation is measured – mass, energy and temperature change.

1. Connect the lamp in series with a variable resistor, an ammeter and a power supply.
2. Connect a voltmeter in parallel across the lamp.
3. Adjust the variable resistor to change the p.d. across the lamp.
4. Record the current and p.d. for a range of at least 6 settings.
5. Reverse the connections to the power supply and repeat to get negative values.
6. Plot a graph of current against p.d.

1. Hang the spring from a clamp stand with a metre ruler clamped vertically beside it.
2. Measure the original length of the spring, reading at eye level using a pointer.
3. Hang a 100 g mass (weight about 1 N) on the spring and measure the new length.
4. Add masses one at a time, measuring the length each time.
5. Calculate extension = new length − original length; calculate weight using W = mg.
6. Plot force against extension; the gradient of the straight section is the spring constant (F = ke).

1. Set the ripple tank up with a lamp above it so the waves are projected onto paper below.
2. Switch on the vibrating bar to make waves.
3. Use a ruler to measure the distance across 10 waves and divide by 10 to find the wavelength.
4. Count the number of waves passing a point in 10 s and divide by 10 to find the frequency.
5. Calculate the speed using v = f × λ.
6. Repeat and calculate a mean (a photo with a ruler in view can make the wavelength easier to measure).

1. Place a small beaker inside a larger beaker and wrap it with one layer of newspaper.
2. Pour a measured volume of hot water (e.g. 80 cm³) into the small beaker and cover it with a lid with a hole for the thermometer.
3. Record the starting temperature and start a stopwatch.
4. Record the temperature every 3 minutes for 20 minutes.
5. Repeat with 2, 3, 4 and 5 layers, keeping the volume and starting temperature of the water the same.
6. Compare the temperature drop after 20 minutes for each thickness (or plot cooling curves).

Useful power: A = 0.85 × 2200 = 1870 W; B = 0.90 × 3000 = 2700 W.
Time to boil: A = 336 000 ÷ 1870 ≈ 180 s; B = 336 000 ÷ 2700 ≈ 124 s, so B is about a minute faster.
Energy wasted per boil: A needs 336 000 ÷ 0.85 ≈ 395 000 J input, wasting about 59 000 J; B needs 336 000 ÷ 0.90 ≈ 373 000 J, wasting about 37 000 J.
B wastes less energy each time, so it costs less to run, but it costs £15 more to buy.
Judgement: B is the better choice for a family that boils the kettle often – it is faster and cheaper to run, so the extra £15 is paid back over time.

Cost over 20 years: diesel = 0.5 + (20 × 0.15) = £3.5 million; wind = £2.0 million, so the wind farm is £1.5 million cheaper overall.
Environment: burning diesel releases carbon dioxide (a greenhouse gas, contributing to climate change) and other pollutants; wind produces no emissions when running. Wind is renewable; diesel will run out.
Reliability: diesel can generate electricity whenever it is needed; wind turbines only work when the wind speed is suitable, so the island may have times without power.
Other: turbines may cause visual and noise pollution and harm birds.
Judgement: replace it – cheaper and cleaner over 20 years – but keep the diesel generator as a backup for calm days.

Temperature drops: A (1 layer) 18 °C; B (1 layer) 9 °C; A (2 layers) 13 °C.
With the same thickness, B is the better insulator – its temperature drop is half that of A (a mean rate of cooling of 0.45 °C/min compared with 0.90 °C/min).
Doubling the thickness of A reduced the temperature drop from 18 °C to 13 °C, so thicker insulation reduces the rate of cooling.
Even with 2 layers, A is still a worse insulator than 1 layer of B.

The temperature of the gas increases, so the particles gain kinetic energy and move faster on average. The particles hit the walls of the can more often and with more force in each collision. This means there is a greater force per unit area on the walls, so the pressure increases. (The volume stays the same because the can is sealed.)

The energy supplied breaks the bonds between the particles, so their potential energy increases. The temperature doesn’t change, so the kinetic energy of the particles stays the same. So the internal energy (total kinetic + potential energy) increases.

The same number of particles are in a smaller volume, so they are closer together. The particles collide with the walls more often (the speed of the particles doesn’t change because the temperature is constant). This gives a larger total force on a smaller area, so the pressure increases.

Common mistake: saying the particles move faster – they don’t, because the temperature is constant.

A current flows through the coil, which is in a magnetic field. The current flows in opposite directions on each side of the coil, so the forces on the two sides act in opposite directions (motor effect), making the coil rotate. The split-ring commutator reverses the direction of the current every half turn, so the forces keep acting to turn the coil the same way.

The alternating current flows through a coil that is in the magnetic field of a permanent magnet. There is a force on the coil (motor effect). Because the current keeps changing direction, the force keeps changing direction, so the coil and the cone attached to it vibrate. The vibrating cone creates pressure variations (compressions and rarefactions) in the air – a sound wave.

An alternating current in the primary coil produces a changing magnetic field in the iron core. The iron core carries this changing field to the secondary coil, where it induces an alternating p.d. across the secondary coil. The secondary coil has fewer turns than the primary coil, so the output p.d. is smaller than the input p.d. (Vₚ/Vₛ = nₚ/nₛ).

1. At first, her weight is greater than air resistance, so there is a downward resultant force and she accelerates.
2. As her speed increases, air resistance increases, so the resultant force decreases and her acceleration decreases.
3. Air resistance becomes equal to her weight; the resultant force is zero, so she falls at a constant speed – terminal velocity.
4. When the parachute opens, air resistance increases suddenly and becomes greater than her weight, so there is an upward resultant force and she decelerates.
5. As she slows down, air resistance decreases until it equals her weight again.
6. She reaches a new, lower terminal velocity, which is slow enough to land safely.

The crumple zone crushes during the collision, which increases the time taken for the car and passengers to stop. The change in momentum is the same, but it happens over a longer time, so the rate of change of momentum is smaller. Force = rate of change of momentum, so the force on the passengers is smaller, reducing injuries. (Equivalently: a longer stopping time means a smaller deceleration, so F = ma is smaller.)

Rolling down the ramp, the gravitational potential energy store decreases and the kinetic energy store increases. Going up the hill, kinetic energy is transferred back to the gravitational potential energy store, so the car slows down. Throughout, work done against friction and air resistance transfers some energy to the thermal store of the surroundings (dissipated). So the car can’t get back to its original height, and eventually stops.

Stopping distance = thinking distance + braking distance.
Thinking distance: tiredness increases the driver’s reaction time, and at a higher speed the car travels further during that time (s = vt), so thinking distance increases. At night the hazard may be seen later.
Braking distance: the car has more kinetic energy at a higher speed (Eₖ = ½mv²), so the brakes must do more work to stop it. The wet road reduces the friction between the tyres and the road, so the braking force is smaller and the car takes a greater distance to stop – it may also skid.
Both parts increase, so the total stopping distance is much greater.

The source emits beta radiation only. Subtracting background: no absorber 400, paper 395. Paper hardly reduces the count-rate, so there is no alpha (alpha would be stopped by paper). The aluminium reduces the count-rate to background level (22 − 20 = 2), so the radiation is stopped by a few mm of aluminium – beta. There is no gamma, because gamma would pass through the aluminium and the count-rate would stay above background.

1. A nebula (cloud of dust and gas) is pulled together by gravity to form a protostar.
2. The temperature rises until hydrogen nuclei fuse to form helium: it becomes a main sequence star.
3. It stays stable because the outward pressure from fusion balances the inward force of gravity.
4. When the hydrogen begins to run out, it becomes a red super giant, fusing helium and heavier nuclei to form elements up to iron.
5. It explodes as a supernova, forming elements heavier than iron and scattering the elements through the universe.
6. What remains becomes a neutron star, or a black hole if the star is massive enough.