GCSE Physics quiz

Energy and electricity: a 2 kg trolley moves at 3 m/s. What is its kinetic energy?

• A. 3 J
• B. 9 J
• C. 12 J
• D. 18 J

Kinetic energy = ½ × mass × speed² = 0.5 × 2 × 3² = 0.5 × 2 × 9 = 9 J. Choosing 18 J means the half was forgotten.

A 4 kg box is lifted 5 m. Using g = 10 N/kg, how much gravitational potential energy does it gain?

• A. 20 J
• B. 40 J
• C. 200 J
• D. 1 000 J

Gravitational potential energy = mass × g × height = 4 × 10 × 5 = 200 J.

A motor transfers 3 600 J of energy in 60 s. What is its power?

• A. 60 W
• B. 216 000 W
• C. 3 540 W
• D. 0.017 W

Power = energy ÷ time = 3 600 ÷ 60 = 60 W. Multiplying instead of dividing gives 216 000, which is a common slip.

A device takes in 120 J of energy and transfers 30 J usefully. What is its efficiency?

• A. 25%
• B. 40%
• C. 75%
• D. 4%

Efficiency = useful output ÷ total input = 30 ÷ 120 = 0.25, which is 25%.

A current of 3 A flows through a 4 Ω resistor. What is the potential difference across it?

• A. 0.75 V
• B. 1.3 V
• C. 7 V
• D. 12 V

Potential difference = current × resistance = 3 × 4 = 12 V.

Two resistors of 2 Ω and 6 Ω are connected in series. What is the total resistance?

• A. 1.5 Ω
• B. 4 Ω
• C. 8 Ω
• D. 12 Ω

In series, resistances add: 2 + 6 = 8 Ω.

Two lamps are connected in parallel to a 6 V cell. Treat the cell as ideal. Which statement is correct?

• A. Each lamp has 6 V across it
• B. 6 V is shared between the two lamps
• C. Current is the same in both lamps whatever their resistances
• D. Total resistance is larger than either lamp’s resistance

Each branch of a parallel circuit is connected directly across the cell, so each has the full 6 V. Splitting the voltage describes a series circuit.

A 2 kW kettle is on for 3 minutes. How much energy does it transfer?

• A. 6 000 J
• B. 120 000 J
• C. 360 000 J
• D. 11 J

Convert first: 2 kW = 2 000 W and 3 minutes = 180 s. Energy = power × time = 2 000 × 180 = 360 000 J. Using 3 for the time gives the 6 000 J trap.

A metal block has a mass of 240 g and a volume of 30 cm³. What is its density?

• A. 0.125 g/cm³
• B. 8 g/cm³
• C. 210 g/cm³
• D. 7 200 g/cm³

Density = mass ÷ volume = 240 ÷ 30 = 8 g/cm³. Dividing the other way gives 0.125.

How much energy is needed to raise the temperature of 2 kg of water by 10 °C? The specific heat capacity of water is 4 200 J/kg °C.

• A. 8 400 J
• B. 84 000 J
• C. 840 J
• D. 420 000 J

Energy = mass × specific heat capacity × temperature change = 2 × 4 200 × 10 = 84 000 J.

A current of 5 A flows for 20 s. How much charge flows?

• A. 4 C
• B. 25 C
• C. 100 C
• D. 0.25 C

Charge = current × time = 5 × 20 = 100 C.

Ice at 0 °C is heated and melts, and its temperature stays at 0 °C while it melts. Why?

• A. No energy is being transferred to it
• B. Particles have stopped moving
• C. Thermometer is not accurate during melting
• D. Energy supplied is used to change the arrangement of the particles, not to raise their average kinetic energy

During a change of state the energy supplied goes into overcoming the forces holding the particles in place, so the temperature stays constant until the change is complete.

Which statement describes isotopes of an element?

• A. Same number of neutrons, different number of protons
• B. Same number of protons, different number of neutrons
• C. Same mass number, different atomic number
• D. Same number of electrons, different number of protons

Isotopes are atoms of the same element, so they have the same number of protons, but they differ in the number of neutrons.

A carbon-14 nucleus has 6 protons. How many neutrons does it have?

• A. 6
• B. 8
• C. 14
• D. 20

Neutrons = mass number − atomic number = 14 − 6 = 8.

A sample has an activity of 80 Bq and a half-life of 3 hours. What is its activity after 9 hours?

• A. 40 Bq
• B. 27 Bq
• C. 20 Bq
• D. 10 Bq

9 hours is 3 half-lives. 80 → 40 → 20 → 10 Bq.

Which type of radiation is the most strongly ionising but the least penetrating?

• A. Alpha
• B. Beta
• C. Gamma
• D. They are all equal

Alpha particles are large and heavily charged, so they ionise strongly but have a very short range in air, which makes them the least penetrating.

A resultant force of 1 200 N acts on a car of mass 800 kg. What is its acceleration?

• A. 0.67 m/s²
• B. 1.5 m/s²
• C. 400 m/s²
• D. 960 000 m/s²

Acceleration = force ÷ mass = 1 200 ÷ 800 = 1.5 m/s².

On the Moon, g = 1.6 N/kg. What is the weight of a 10 kg object there?

• A. 6.25 N
• B. 10 N
• C. 16 N
• D. 160 N

Weight = mass × gravitational field strength = 10 × 1.6 = 16 N. Its mass stays 10 kg.

A cyclist travels 150 m in 20 s at a steady speed. What is the speed?

• A. 130 m/s
• B. 0.13 m/s
• C. 3 000 m/s
• D. 7.5 m/s

Speed = distance ÷ time = 150 ÷ 20 = 7.5 m/s.

A wave has a frequency of 50 Hz and a wavelength of 6 m. What is its wave speed?

• A. 8.3 m/s
• B. 56 m/s
• C. 300 m/s
• D. 0.12 m/s

Wave speed = frequency × wavelength = 50 × 6 = 300 m/s.

A wave has a frequency of 4 Hz. What is its period?

• A. 0.25 s
• B. 4 s
• C. 0.4 s
• D. 16 s

Period = 1 ÷ frequency = 1 ÷ 4 = 0.25 s.

Which of these waves is longitudinal?

• A. Light
• B. Ripples on water
• C. Sound in air
• D. Radio waves

In sound, the particles of the medium oscillate parallel to the direction the wave travels. Light and radio waves are transverse.

What does the magnetic field around a long straight wire carrying a current look like?

• A. Straight lines parallel to the wire
• B. Concentric circles around the wire
• C. Lines pointing directly away from the wire
• D. There is no magnetic field

A current produces a magnetic field in circles centred on the wire, and the direction reverses if the current reverses.

A satellite orbits Earth in a circle at constant speed. Which statement is correct?

• A. Its velocity is constant because its speed is constant
• B. It has no resultant force on it
• C. Its velocity is changing because its direction is changing
• D. It must have a rocket engine firing all the time

Velocity includes direction, so it changes as the satellite turns. A resultant force towards Earth, from gravity, causes this change of direction.