GCSE Energy (Physics Paper 1) 2 — Questions and Answers
Question 1: What does the specific heat capacity of a substance tell you?
- The energy needed to melt 1 kg of the substance
- The energy needed to raise the temperature of 1 kg of the substance by 1 °C (Correct answer)
- The temperature at which the substance boils
- The energy released when 1 kg of the substance burns
Correct answer: The energy needed to raise the temperature of 1 kg of the substance by 1 °C
Specific heat capacity is the energy required to raise the temperature of 1 kg of a substance by 1 °C, measured in J/kg °C.
Specific heat capacity (c) appears in the equation ΔE = m c Δθ, where ΔE is the change in thermal energy, m is mass and Δθ is the temperature change. Water has a high specific heat capacity of about 4200 J/kg °C, meaning it takes a lot of energy to warm up and it cools slowly, which is why it is used in central heating systems and why coastal climates are mild. The energy needed to melt a substance is a different quantity called specific latent heat.
Question 2: How much energy is needed to raise the temperature of 0.5 kg of water from 20 °C to 60 °C? (Specific heat capacity of water = 4200 J/kg °C)
- 21,000 J
- 42,000 J
- 84,000 J (Correct answer)
- 126,000 J
Correct answer: 84,000 J
ΔE = m c Δθ = 0.5 × 4200 × (60 − 20) = 0.5 × 4200 × 40 = 84,000 J.
Use ΔE = m c Δθ. The mass is 0.5 kg, the specific heat capacity is 4200 J/kg °C and the temperature change is 60 − 20 = 40 °C. Multiplying: 0.5 × 4200 = 2100, and 2100 × 40 = 84,000 J (84 kJ). Always use the change in temperature, not the final temperature, in this equation.
Question 3: Which statement about the principle of conservation of energy is correct?
- Energy can be created but not destroyed
- Energy can be destroyed but not created
- Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed (Correct answer)
- Energy is always destroyed when a machine is used
Correct answer: Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed
Energy is conserved: the total energy in a closed system stays the same, it is only transferred between stores or dissipated.
The principle of conservation of energy states that energy cannot be created or destroyed, only transferred from one store to another. In every real transfer some energy is dissipated, meaning it spreads out into the surroundings (usually as thermal energy) where it is no longer useful, but it still exists. This is why the energy input to a device always equals the useful output plus the wasted output.
Question 4: Which of these changes would reduce the rate of thermal energy transfer from a house?
- Using thinner walls
- Using walls made from a material with a higher thermal conductivity
- Installing loft insulation with a low thermal conductivity (Correct answer)
- Increasing the temperature difference between inside and outside
Correct answer: Installing loft insulation with a low thermal conductivity
Insulation with a low thermal conductivity slows the rate at which energy is conducted out of the building.
The rate of cooling of a building depends on the thickness of its walls, the thermal conductivity of the materials, and the temperature difference between inside and outside. Thicker walls and lower thermal conductivity both reduce the rate of energy transfer by conduction. Loft insulation, cavity wall insulation and double glazing all work by trapping air, which has a very low thermal conductivity.
Question 5: A spring with a spring constant of 200 N/m is stretched by 0.1 m. How much elastic potential energy is stored?
- 1 J (Correct answer)
- 2 J
- 10 J
- 20 J
Correct answer: 1 J
Ee = ½ k e² = 0.5 × 200 × 0.1² = 0.5 × 200 × 0.01 = 1 J.
Elastic potential energy stored in a stretched (or compressed) spring, as long as the limit of proportionality is not exceeded, is Ee = ½ k e², where k is the spring constant in N/m and e is the extension in metres. Here 0.1² = 0.01, so ½ × 200 × 0.01 = 1 J. A common error is forgetting to square the extension, which would wrongly give 10 J.
Question 6: Which is an advantage of using nuclear power stations rather than coal-fired power stations for generating electricity?
- Nuclear fuel is a renewable resource
- Nuclear power stations produce no carbon dioxide during generation (Correct answer)
- Nuclear waste is completely safe to dispose of
- Nuclear power stations are cheap and quick to decommission
Correct answer: Nuclear power stations produce no carbon dioxide during generation
Nuclear reactors do not burn fuel, so they release no carbon dioxide while generating electricity, unlike coal.
Nuclear power stations release energy from the nuclear store of uranium fuel by fission, so no fossil fuel is burned and no carbon dioxide is produced during generation. However, uranium is non-renewable, the radioactive waste must be stored safely for thousands of years, and decommissioning a nuclear plant is expensive and slow. Exam questions often ask you to weigh these advantages and disadvantages against each other.
GCSE Energy (Physics Paper 1) 2
What does the specific heat capacity of a substance tell you?