O-LevelPhysicsElectricity5054/22 · Oct/Nov 2018 · Q48 Marks
A house has several solar panels on the roof. These panels use energy from the Sun both to generate electricity and to raise the temperature of water that passes through tubes inside the panels.
- (a)(i)The panels on the roof of the house have a black surface. State how energy from the Sun travels through space before it reaches the Earth.[1]
- (a)(ii)Explain the advantage of using panels that have a black surface.[2]
- (b)(i)On one occasion, the panels are supplying an electric current of 15A at a voltage of 24 V. Calculate the electrical energy generated by the panels in one hour.[2]
- (b)(ii)In the same time, 51 kg of cold water is pumped through the panels. The temperature of the water increases from 16°C to 45°C. The specific heat capacity of water is 4200J/(kg°C). Calculate the increase in thermal energy of the water.[3]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.
- [1] radiation or infrared (radiation / waves) or light
- [1] it/ a black surface is a good absorber / poor reflector of radiation
- [1] more energy / power output or more electricity produced
- [1] (P =) VIt or 24 × 15 × 3600 or 24 × 15 × 60 or 22 000 (J)
- [1] 1.3 × 10⁶ J
- [1] (ΔQ =) mcΔT or 29 (°C) or 45 – 16 (°C)
- [1] 51 × 4200 x 29 or 51 × 4200 × (45 – 16)
- [1] 6.2 x 10⁶ J
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