Fig. 1 shows the electrical circuit used in a wildlife pond at a nature centre. During sunny weather, a solar panel charges a battery. The battery provides ...
Question 1 Report
Fig. 1 shows the electrical circuit used in a wildlife pond at a nature centre. During sunny weather, a solar panel charges a battery. The battery provides a potential difference of 18 V to a pump motor. A current of 2.5 A flows through the cable and the coil in the motor. The motor moves water through a filter for 4.0 minutes. Some electrical energy is transferred usefully to the moving water, but some is transferred to the surroundings as sound and thermal energy.
Fig. 1
(a) What is meant by potential difference? [1]
(b) Use the values in Fig. 1 to calculate the electrical power supplied to the motor. [2]
(c) Use your answer to part (b) to calculate the electrical energy transferred by the battery in 4.0 minutes. [3]
(d) Explain why the useful energy transferred to the water is less than the electrical energy supplied to the motor. [2]
(e) Give two changes that would allow the pump to operate for longer before the battery needs charging. [2]
Answer Details
(a) Potential difference is the energy transferred, or work done, per unit charge. [1]
(b) \[P=VI=18\text{ V}\times2.5\text{ A}=45\text{ W}\] [2]
(c) \[4.0\text{ min}=4.0\times60=240\text{ s}\] \[E=Pt=45\text{ W}\times240\text{ s}=10800\text{ J}\] [3]
(d) Some energy is transferred thermally because of resistance in the coil or cable and because of friction in moving parts. Some may also be transferred as sound. Therefore not all electrical input energy becomes useful energy transferred to the water. [2]
(e) Two acceptable changes are using a battery with greater capacity, reducing current by using a lower-power pump, using a more efficient pump motor, charging the battery for longer with the solar panel, or switching the pump off when circulation is not needed. [2]
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