Electric circuitsEdexcel A-Level Physics: Topic test

20 questions, 54 marks

Edexcel A-Level Physics

Electric circuits topic test

Total 54 marks

Name

Class

Date

1
In a research accelerator a beam of protons passes a fixed point at a rate of 2.5 × 10¹² protons per second. Each proton carries a charge of 1.6 × 10⁻¹⁹ C. The beam is then stopped by a metal target. Before reaching the target each proton has been accelerated through a potential difference of 5.0 kV.
(a)
What is the current in the beam?
[1 mark]
A1.6 × 10³¹ A
B4.0 × 10⁻⁷ A
C2.5 × 10¹² A
D4.0 × 10⁻⁴ A
(b)
What charge reaches the target in 1.0 minute?
[1 mark]
A6.7 × 10⁻⁹ C
B4.0 × 10⁻⁷ C
C2.4 × 10⁻⁶ C
D2.4 × 10⁻⁵ C
(c)
Calculate the rate at which energy is delivered to the target.
[2 marks]
Total for question 1: 4 marks
2
A 9.0 V battery of negligible internal resistance is connected across three resistors in parallel: a 6.0 Ω resistor, an 18 Ω resistor and a third resistor R of unknown value. The current in the battery is 3.2 A.
(a)
What is the current in the resistor R?
[1 mark]
A1.2 A
B1.7 A
C5.2 A
D2.0 A
(b)
What is the resistance of R?
[1 mark]
A2.8 Ω
B0.13 Ω
C7.5 Ω
D11 Ω
(c)
State why the potential difference across each of the three resistors is 9.0 V, and explain this in terms of energy.
[2 marks]
Total for question 2: 4 marks
3
A constantan wire is used as a standard resistor. It has length 2.00 m and diameter 0.30 mm. The resistivity of constantan is 4.9 × 10⁻⁷ Ω m.
(a)
Calculate the resistance of the wire.
[3 marks]
(b)
The wire is connected across a 6.0 V cell of negligible internal resistance. It is then replaced by a constantan wire of the same length but of diameter 0.60 mm. Explain how the power dissipated changes and calculate the new power.
[4 marks]
Total for question 3: 7 marks
4
A semiconductor temperature sensor is an NTC thermistor. Its resistance is 2.0 kΩ at 20 °C and 400 Ω at 60 °C. Copper lead wires of the same cross-sectional area connect it to a circuit. At 20 °C the thermistor material has 4.0 × 10²¹ conduction electrons per m³, and copper has 8.5 × 10²⁸ per m³.
(a)
The thermistor and a copper lead carry the same current. Compare the drift speeds of the electrons in them, and explain why heating increases the resistance of copper but decreases the resistance of the thermistor.
[6 marks]
(b)
The thermistor is connected in series with a 1.0 kΩ fixed resistor across a 5.0 V supply of negligible internal resistance, and the output is taken across the fixed resistor. Calculate the output at 20 °C and at 60 °C, explain the change in terms of a potential divider, and state how the circuit could be altered so that the output falls as the temperature rises.
[6 marks]
Total for question 4: 12 marks
5
An electric-car home charger operates from a 230 V supply and delivers 7.4 kW to the car battery. The charging cable has a total resistance of 0.050 Ω. A car is charged at this power for 5.0 hours.
(a)
What is the current in the cable?
[1 mark]
A0.031 A
B1.7 × 10⁶ A
C32 A
D16 A
(b)
What power is dissipated as heat in the cable?
[1 mark]
A52 W
B1.6 W
C7.4 kW
D1.0 × 10³ W
(c)
Calculate the energy dissipated as heat in the cable during the 5.0 hours.
[2 marks]
Total for question 5: 4 marks
6
A rechargeable cell of e.m.f. 3.6 V has a small internal resistance. When it is connected across a load resistor of 11 Ω, the current in the circuit is 0.30 A.
(a)
What is the terminal potential difference of the cell?
[1 mark]
A3.6 V
B0.30 V
C3.9 V
D3.3 V
(b)
What is the internal resistance of the cell?
[1 mark]
A12 Ω
B1.0 Ω
C11 Ω
D0.30 Ω
(c)
Calculate the energy wasted inside the cell in 10 minutes.
[2 marks]
Total for question 6: 4 marks
7
A 10 V supply of negligible internal resistance is connected across a potential divider made of a 2.0 kΩ resistor in series with a 3.0 kΩ resistor. The output is taken across the 3.0 kΩ resistor.
(a)
Calculate the output p.d. when nothing is connected to the output terminals.
[3 marks]
(b)
A load of resistance 6.0 kΩ is now connected across the output terminals. Calculate the new output p.d.
[4 marks]
Total for question 7: 7 marks
8
A 12.0 V battery of internal resistance 0.50 Ω supplies a 5.0 Ω heater through two copper cables. Each cable is 20 m long with a cross-sectional area of 2.5 × 10⁻⁶ m². The resistivity of copper is 1.7 × 10⁻⁸ Ω m.
(a)
Calculate the power dissipated in the heater and the terminal potential difference of the battery.
[6 marks]
(b)
Evaluate whether replacing the cables with ones of twice the cross-sectional area would make the system much more efficient.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).