The questions are on the energy transfers test. Take it under real conditions before reading the mark scheme.
Quick answer: An energy transfer is the movement of energy from one store to another or its change from one form to another. This mark scheme gives the model answers and the marks for the 8 questions of the grade 7 science test on energy transfers, from conservation of energy to insulating a kettle, with the equivalent answers to accept.
Model answers with the marks available. Award method marks for correct substitution even if the final arithmetic has a slip, and look for the key ideas in the explanations rather than exact wording.
Level: Grade 7 science (Year 8 · Class 7) · Curriculum: MS-PS3-5
Question 1 Conservation of energy (2 marks)
Energy cannot be created or destroyed; it can only be transferred from one store to another. Example: the electrical energy of a lamp is partly transferred as wasted thermal energy.
Marking: 1 mark for the law; 1 mark for a valid example.
Question 2 Radio chain (3 marks)
- Chemical → electrical → sound.
- Thermal energy in the wires and circuit.
Marking: (a) 1 mark for each correct link; (b) 1 mark.
Question 3 Water pump Sankey (3 marks)
- 360 J.
- 240 J.
- 360 ÷ 600 × 100 = 60 %.
Marking: 1 mark for each part.
Question 4 Gas ring (3 marks)
- Efficiency = (useful energy output ÷ total energy input) × 100 %.
- 1800 ÷ 3000 × 100 = 60 %.
Marking: (a) 1 mark; (b) 1 mark for substitution, 1 for the answer.
Question 5 Hard to reuse (2 marks)
The thermal energy spreads out into the surrounding air, warming a very large amount of air by a tiny amount. It is too spread out to be gathered, so it cannot do useful work.
Marking: 1 mark for energy spreading to the surroundings; 1 mark for too spread out or too little warming to use.
Question 6 Compare two devices (3 marks)
- A: 40 ÷ 50 × 100 = 80 %. B: 36 ÷ 40 × 100 = 90 %.
- A wastes 10 J and B wastes 4 J, so device B wastes less.
Marking: (a) 1 mark each; (b) 1 mark.
Question 7 Impossible claim (2 marks)
This would create 50 J of energy from nothing, which breaks the law of conservation of energy. The output of a machine is always less than or equal to the input, so its efficiency cannot exceed 100 %.
Marking: 1 mark for energy cannot be created; 1 mark for efficiency cannot be more than 100 %.
Question 8 Insulating a kettle (2 marks)
The efficiency increases. The insulation reduces the thermal energy transferred to the air, so a larger share of the electrical energy ends up in the water.
Marking: 1 mark for increase; 1 mark for less thermal energy escaping to the surroundings.
