ElectricityAQA GCSE Physics: Topic test

20 questions, 54 marks

AQA GCSE Physics

Electricity topic test

Total 54 marks

Name

Class

Date

1
A student connects a 4 ohm resistor and a 6 ohm resistor in series with a 20 V battery, forming a single closed loop.
(a)
What is the total resistance of the circuit?
[1 mark]
A2 ohms
B10 ohms
C24 ohms
D0.42 ohms
(b)
Which equation links potential difference, current and resistance for this circuit?
[1 mark]
AV = IR
BV = I/R
CV = I + R
DV = R/I
(c)
Calculate the current in the circuit. Give the equation used, your working, and the final answer with unit.
[2 marks]
Total for question 1: 4 marks
2
An electronics hobbyist connects a light-emitting diode (LED) into a test circuit with a battery and a protective fixed resistor, and investigates how the current through the LED changes as the potential difference across it is varied in both directions.
(a)
Which statement correctly describes the behaviour of the LED in this test?
[1 mark]
AIt allows current to flow easily in one direction only, with very high resistance in the reverse direction
BIt has the same resistance regardless of the direction of current flow
CIts resistance decreases as the temperature of the LED increases
DIts resistance decreases as the light falling on it increases
(b)
Which graph shape would correctly describe the current-potential difference behaviour of the LED as the applied potential difference is increased from a large negative value to a large positive value?
[1 mark]
AA straight line through the origin
BA curve that is symmetrical about the origin, current increasing more steeply at higher potential difference in both directions
CAlmost no current until a threshold positive potential difference is reached, then a steep rise; almost no current for negative potential difference
DA straight horizontal line, current constant regardless of potential difference
(c)
Explain why the fixed resistor is included in the test circuit in series with the LED.
[2 marks]
Total for question 2: 4 marks
3
An engineer is designing the wiring for a small workshop with three power tools that may each be used at different times, and is deciding whether to connect the sockets in series or in parallel.
(a)
Explain why the sockets should be connected in parallel rather than in series, referring to both potential difference and current.
[3 marks]
(b)
Two of the power tools, of resistance 20 ohms and 30 ohms, are connected in parallel across the 230 V mains supply. Calculate the total current drawn from the supply when both tools are switched on together.
[4 marks]
Total for question 3: 7 marks
4
A regional electricity company generates power at a power station and transmits it to towns through the National Grid using step-up and step-down transformers, before it reaches domestic sockets wired with three-core cable.
(a)
Explain why the National Grid transmits electrical power at a high voltage using step-up transformers, and why step-down transformers are then used near towns and cities before the electricity reaches consumers.
[6 marks]
(b)
A technician finds that the insulation on the live wire inside an old domestic appliance has worn away, allowing the live wire to touch the appliance's metal casing. Explain the danger this creates, and evaluate two features of the three-core cable and appliance design that protect users against it.
[6 marks]
Total for question 4: 12 marks
5
A gardener builds a frost-alarm circuit containing a thermistor connected in series with a fixed resistor, a battery, and a buzzer that sounds once the current in the circuit rises above a set value as the temperature falls.
(a)
How does the resistance of the thermistor change as the temperature falls towards freezing?
[1 mark]
AIt decreases
BIt stays exactly the same
CIt becomes zero
DIt increases
(b)
As the thermistor's resistance changes in this way, what happens to the current in the circuit, and why does the buzzer sound as the temperature falls?
[1 mark]
AThe current decreases as resistance rises, so the buzzer would never sound
BThe current increases as resistance falls, tripping the buzzer at low temperature
CThe current stays constant because the potential difference automatically adjusts
DThe current becomes reversed, triggering the buzzer
(c)
The fixed resistor has a resistance of 500 ohms and the battery supplies 6 V. At a certain low temperature the thermistor's resistance has fallen to 100 ohms. Calculate the current in the circuit at this temperature.
[2 marks]
Total for question 5: 4 marks
6
A designer builds a streetlight control circuit using a light-dependent resistor (LDR) connected in series with a fixed resistor, so that the streetlight switches on automatically once it becomes dark enough.
(a)
How does the resistance of the LDR change as the light intensity falling on it decreases at dusk?
[1 mark]
AIt decreases
BIt stays exactly the same
CIt becomes zero
DIt increases
(b)
Which other component could be used, in place of the LDR, to build a circuit that automatically responds to a change in temperature rather than light?
[1 mark]
AA diode
BA fixed resistor
CA thermistor
DA fuse
(c)
Explain, in terms of resistance and potential difference, why placing the LDR in series with a fixed resistor allows the circuit to detect when it becomes dark.
[2 marks]
Total for question 6: 4 marks
7
A café owner compares two kettles. Kettle X is connected to the 230 V mains supply and draws a current of 10 A. Kettle Y has a heating element of resistance 21.2 ohms connected to the same 230 V supply.
(a)
Calculate the power of Kettle X and the power of Kettle Y, and state which kettle has the greater power.
[3 marks]
(b)
The café uses Kettle X for 15 minutes every day. Calculate the energy transferred by Kettle X in one day, in joules, and in kilowatt-hours.
[4 marks]
Total for question 7: 7 marks
8
During refuelling at an airport, friction between the fuel and the inside of the fuel pipe transfers electrons between the fuel and the pipe, building up static charge, in a system that also uses earthed conducting equipment as a safety measure.
(a)
Explain, in terms of the transfer of electrons, how friction between the fuel and the fuel pipe causes a build-up of static charge, and why this creates a risk of sparking during refuelling.
[6 marks]
(b)
Evaluate two precautions that engineers use to reduce the risk of a dangerous spark occurring during refuelling.
[6 marks]
Total for question 8: 12 marks

End of questions