O-LevelPhysicsEnergy & Work5054/22 · May/June 2018 · Q915 Marks
Wind energy is a renewable energy source. A wind turbine and generator convert energy in the wind to electrical energy in a generator. Fig. 9.1 shows some wind turbines. [Figure 9.1 shows several wind turbines in a field.] [Figure 9.2 shows a blank grid with y-axis labelled "voltage/V" from -500 to 500 and x-axis labelled "time/s" from 0 to 0.03, with markings at 0, 0.01, 0.02, 0.03.]
- (a)(i)State what is meant by a renewable energy source.[1]
- (a)(ii)State the name of one other renewable energy source.[1]
- (a)(iii)1.Some methods of generating electricity cause much more global warming than wind energy. State one method of generating electricity that causes a large amount of global warming.[1]
- (a)(iii)2.Describe, in outline, how the method you have chosen causes a significant amount of global warming.[1]
- (b)(i)During a 30 minute period, a mass of 4.2 × 10⁷kg of air enters the turbine with a speed of 15m/s. Calculate the kinetic energy of the air that enters the turbine in 30 minutes. energy = .....................................................[2][2]
- (b)(ii)The electrical power output of the generator connected to the turbine is 8.4 × 10⁵W. Calculate the electrical energy output from the turbine in 30 minutes. energy output = .....................................................[2][2]
- (b)(iii)Calculate the efficiency of the turbine and generator in converting the kinetic energy of the air to electrical energy. efficiency = .....................................................[2][2]
- (c)(i)The generator contains a coil that rotates between the poles of a magnet. The coil rotates 50 times in one second and produces an alternating voltage output with a maximum value of 500 V. On the grid in Fig. 9.2, sketch a voltage-time graph showing the output voltage.[2]
- (c)(ii)1.The output voltage from the generator is stepped up by a transformer. The electrical energy then passes along a transmission line to a distant house. Explain why a high voltage is used for the transmission of electrical energy,[2]
- (c)(ii)2.a transformer is used to connect the transmission line to the house.[1]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.
- [1] (a)(i) will not run out or infinite or being replaced
- [1] (a)(ii) solar / Sun, tidal, geothermal, biomass, hydroelectric, water waves
- [1] (a)(iii)1 (burning) use of a fossil fuel, e.g. coal, oil, natural gas etc.
- [1] (a)(iii)2 produces carbon dioxide or greenhouse gases (absorb infra-red from Earth)
- [1] (b)(i) (E=) ½mv² seen in any form algebraic or numerical
- [1] (b)(i) 4.7 x 10⁹ J
- [1] (b)(ii) (E=)Pt seen in any form algebraic or numerical
- [1] (b)(ii) 1.5 × 10⁹ J
- [1] (b)(iii) (efficiency=) (energy) output / (energy) input in any form
- [1] (b)(iii) 0.32 or 32%
- [1] (c)(i) all peaks and troughs at 500 and -500 to within one small square and roughly sinusoidal
- [1] (c)(i) one wave takes 0.02 s within one small square
- [1] (c)(ii)1 less energy loss / heat loss / power loss / more efficient
- [1] (c)(ii)1 low(er) currents (in line) or thin(ner) wires can be used
- [1] (c)(ii)2 step down transformer or voltage reduced (to 240 V) or otherwise voltage dangerous
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