Generating & Distributing Electricity & Household UseOxford AQA IGCSE Physics: Topic test

20 questions, 54 marks

Oxford AQA IGCSE Physics

Generating & Distributing Electricity & Household Use topic test

Total 54 marks

Name

Class

Date

1
A camper uses a hand-crank generator: turning a handle rotates a coil of wire within a strong magnetic field created by fixed permanent magnets, inducing a potential difference that charges a mobile phone.
(a)
If the camper turns the handle faster, what happens to the induced potential difference?
[1 mark]
AIt increases
BIt decreases
CIt stays the same
DIt changes direction but not size
(b)
What name is given to the effect by which turning the coil within the magnetic field induces a potential difference?
[1 mark]
AThe motor effect
BThe generator effect
CThe transformer effect
DThe thermoelectric effect
(c)
State two changes, other than turning the handle faster, that would increase the size of the induced potential difference.
[2 marks]
Total for question 1: 4 marks
2
A desktop fan contains a small electric motor: a coil of wire sits inside the magnetic field of a curved permanent magnet, and when current flows through the coil it experiences a force that makes the coil rotate.
(a)
In the fan motor, what happens to the direction of the force on the coil if the current direction is reversed, with the magnetic field unchanged?
[1 mark]
AThe force stays in the same direction
BThe force disappears completely
CThe force direction reverses
DThe force becomes twice as strong
(b)
Which change would increase the force on the coil in the fan's motor?
[1 mark]
ARemoving the magnetic field
BDecreasing the length of wire within the field
CDecreasing the current flowing through the coil
DIncreasing the current flowing through the coil
(c)
Explain why the coil experiences no force at all at one point during each full rotation, and state what must be true about the current and field directions when this happens.
[2 marks]
Total for question 2: 4 marks
3
A factory has its own step-down transformer that reduces the potential difference from the 11 000 V local distribution line to 400 V for use on site. The transformer's primary coil has 5500 turns.
(a)
Explain why electricity is transmitted at a high potential difference before being stepped down for use, referring to current and energy losses.
[3 marks]
(b)
Calculate the number of turns on the secondary coil, and calculate the secondary current for a primary current of 20 A, assuming the transformer is 100% efficient.
[4 marks]
Total for question 3: 7 marks
4
A geothermal power station uses naturally heated underground steam to spin a turbine connected to a generator. Electricity produced at the power station is stepped up by a transformer for transmission along cables to a town, then stepped down again by a substation transformer before reaching consumers.
(a)
Explain how the geothermal power station generates electricity, referring to the generator effect, and explain how reversing the direction the turbine spins would affect the output.
[6 marks]
(b)
Explain why the electricity is stepped up before transmission and stepped down before reaching consumers, and, given that the power station generates electricity at 25 000 V but the transmission cables operate at 275 000 V, calculate the turns ratio (n_p : n_s) needed in the step-up transformer.
[6 marks]
Total for question 4: 12 marks
5
An electrician uses an oscilloscope to compare two electrical supplies. For the first supply, the trace shows a constant, unchanging horizontal line. For the second supply, the trace shows a repeating wave completing 50 full cycles every second.
(a)
The first supply's trace is a constant, unchanging horizontal line. What type of supply is this?
[1 mark]
AAn alternating current (ac) supply
BA direct current (dc) supply
CNo supply is connected
DAn intermittent supply that switches on and off
(b)
Which of the following safety devices can disconnect a circuit within milliseconds and be reset afterwards, unlike a traditional fuse?
[1 mark]
AA circuit breaker
BA rewireable fuse
CAn earth wire alone
DDouble insulation
(c)
Calculate the period of the second (ac) supply from its frequency of 50 Hz, and state the number of complete cycles it completes in 5 seconds.
[2 marks]
Total for question 5: 4 marks
6
A tumble dryer, rated at 2.5 kW, is run by a household for 90 minutes on a laundry day. Electricity costs 28p per kWh.
(a)
Which unit is commonly used by electricity meters and household bills to measure the energy transferred by mains electricity?
[1 mark]
AThe joule (J)
BThe watt (W)
CThe volt (V)
DThe kilowatt-hour (kWh)
(b)
As current flows through the tumble dryer's heating element, which energy transfer occurs?
[1 mark]
AThermal energy is transferred to electrical energy
BElectrical energy is transferred to kinetic energy only
CElectrical energy is transferred to thermal energy
DElectrical energy is transferred to chemical energy
(c)
Calculate the energy transferred by the tumble dryer, in kilowatt-hours, and the cost of running it, given electricity costs 28p per kWh.
[2 marks]
Total for question 6: 4 marks
7
An electric toothbrush contains a small dc motor: a coil of wire sits within the magnetic field of fixed permanent magnets, and current from a rechargeable battery flows through the coil to make it rotate.
(a)
State Fleming's left-hand rule, and explain what each of the three quantities it represents (thumb, first finger, second finger) corresponds to in the motor effect.
[3 marks]
(b)
Describe three separate changes that could be made to the toothbrush motor's coil and magnets to increase the force on the coil, and state what happens to the direction of the force if the current direction is reversed.
[4 marks]
Total for question 7: 7 marks
8
An electric bicycle has a coil of wire mounted on the wheel hub, positioned within the magnetic field of fixed magnets. When the rider pedals uphill, the battery drives a current through the coil, and the wheel is driven round by the resulting force. When freewheeling downhill, the spinning wheel instead turns the coil within the magnetic field, charging the battery.
(a)
Explain, using ideas about the motor effect, how current flowing through the coil while pedalling uphill produces a force that drives the wheel round, and describe two ways the force could be increased for a steeper climb.
[6 marks]
(b)
Explain, using ideas about the generator effect, why freewheeling downhill charges the battery, and explain two factors that would affect how much charge is delivered to the battery for the same downhill distance.
[6 marks]
Total for question 8: 12 marks

End of questions