Students investigate the efficiency of an electric motor - Edexcel - GCSE Physics - Question 4 - 2018 - Paper 1
Question 4
Students investigate the efficiency of an electric motor.
(a) The students measure the input power and the output power of the motor.
Complete the sentence by putti... show full transcript
Worked Solution & Example Answer:Students investigate the efficiency of an electric motor - Edexcel - GCSE Physics - Question 4 - 2018 - Paper 1
Step 1
a) Complete the sentence
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Answer
The power of the motor is the rate of transfer of C energy.
Step 2
b) Sketch a graph for an alternating current of frequency 0.5 Hz
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The graph should show a sinusoidal waveform oscillating between positive and negative values, representing the AC current, with a frequency of 0.5 Hz indicating one complete cycle every 2 seconds.
Step 3
c) Explain what is meant by an efficiency of 40%
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An efficiency of 40% means that the electric motor converts 40% of the electrical energy supplied into useful work or output energy, while the remaining 60% is lost as waste energy, typically in the form of heat.
Step 4
d) The motor has a power rating of 15 W.
(i) Calculate the energy supplied to the motor in 3 minutes.
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The energy supplied can be calculated using the formula:
extEnergy=extPowerimesextTime
where Power = 15 W and Time = 3 ext{ minutes} = 0.05 ext{ hours}:
extEnergy=15extWimes0.05exth=0.75extkWh
The unit of energy is kilowatt-hours (kWh).
Step 5
d) The motor has a power rating of 15 W.
(ii) Calculate the cost of running the motor for 3 minutes.
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To find the cost, first calculate the energy supplied in kWh (which we already found to be 0.75 kWh) and then multiply it by the cost per kWh:
