1
1
The electric starter motor in a car is switched on and off using a relay.
The power of the starter motor is 1.8 kW and it is also operated by the 12 V car battery.
Calculate the current in the starter motor when it is used.
current = ................................................... [2]
[Total: 2]
2
The diagram shows how the electromotive force (e.m.f.) of a 60 Hz alternating current (a.c.) power
supply varies with time.
e.m.f.
0
0
time
time period
(a) Calculate the time period of the a.c.
time period = ..............................................
[1]
2
(b) The diagram shows this power supply connected in a circuit.
A
B
In each time period of the a.c., 1.5 × 10
–19
on an electron is 1.6 × 10 C.
C
17
electrons pass through component A. The charge
Calculate the average current in the circuit during one time period.
current = ..............................................
[3]
[Total: 4]
3
The diagram shows an alternating current (a.c.) power supply connected in a circuit.
A
B
C
State the name of component A.
.......................................................
[1]
[Total: 1]
3
4
Two resistors of resistance 2.0 Ω and 3.0 Ω are connected in parallel.
Calculate the combined resistance of the resistors in this arrangement.
resistance = ..............................................
[3]
[Total: 3]
5
The diagram shows a circuit with components B and C connected to a direct current (d.c.) power
supply of e.m.f. 12 V.
B
C
The current in the circuit is 0.35 A.
Calculate the power delivered by the power supply to the circuit.
power = ..............................................
[2]
[Total: 2]
4
6
The diagram shows a circuit including a 12 V battery and two identical lamps.
A
Q
(a) When the switch is closed, the ammeter reading is 2.4 A.
Calculate the total resistance of the circuit.
resistance = .....................................................
[2]
resistance of Q = .....................................................
[2]
(b) Each lamp has a resistance of 3.0 Ω.
Calculate the resistance of Q.
[Total: 4]
5
7
The diagram shows a circuit including a 12 V battery and two identical lamps.
A
Q
When the switch is closed, the ammeter reading is 2.4 A.
Each lamp has a resistance of 3.0 Ω.
Calculate the power supplied to one lamp.
power = .....................................................
[3]
[Total: 3]
8
The diagram shows an electric circuit which is in a cool room.
(a) The temperature of the thermistor increases and the buzzer turns on.
State and explain how the increase in temperature affects the current in the thermistor.
...........................................................................................................................................
...........................................................................................................................................
[2]
6
(b) Suggest a possible use for the circuit shown in the diagram above.
...........................................................................................................................................
[1]
[Total: 3]
9
The diagram shows a source E of e.m.f. 60 V in a circuit.
E
10 Ω
H
X
The heater H has a resistance of 22.5 Ω and the potential difference (p.d.) across it is 45 V.
Calculate:
(a) the power of the heater
power = .....................................................
[3]
p.d. = .....................................................
[2]
current = .....................................................
[2]
(b) the p.d. across resistor X
(c) the current in the 10 Ω resistor.
[Total: 7]
10 The diagram shows an incomplete electrical circuit.
7
(a) A student completes the circuit and measures the current in the 6.0 Ω resistor.
On the diagram, draw an ammeter symbol in one gap and straight lines to indicate wires in
the other gaps to show how the student should do this.
[1]
(b) A voltmeter is connected to measure the potential difference (p.d.) across the 4.0 Ω resistor.
On the diagram, draw a voltmeter symbol connected in the correct position.
[2]
(c) With the circuit completed, the current in the 2.0 Ω resistor is 2.5 A.
Calculate the current in the 6.0 Ω resistor.
current = ..............................................
[4]
[Total: 7]
11
An electric heater contains two heating elements R1 and R2. An electric motor operates a fan. The
fan blows cool air over the heating elements.
The diagram shows the circuit.
8
The heater is powered by a mains supply of e.m.f. 240 V.
Switches S1 and S2 are closed. Heating element R1 gets hot. The resistance of R1 is 30 Ω.
(a) Calculate the current in heating element R1.
current = ..............................................
[1]
(b) Calculate the power produced in heating element R1.
power = ..............................................
[2]
(c) The resistance of heating element R2 is 60 Ω.
Switches S1, S2 and S3 are closed.
(i)
State and explain how the current in R2 compares with the current in R1.
................................................................................................................................
................................................................................................................................
................................................................................................................................
[2]
9
(ii) The current in the motor is 0.10 A. The cable from the electric heater to the plug for the
mains socket is safe when the current in it is less than 20 A.
Suggest and explain a suitable fuse rating for this circuit.
................................................................................................................................
................................................................................................................................
................................................................................................................................
................................................................................................................................
[2]
[Total: 7]
12 (a) The diagram shows an electrical circuit. The resistor has a resistance of 4.0 Ω. The reading
on the voltmeter is 3.0 V
Calculate the current in the resistor.
current = ..............................................
[2]
10
(b) The diagram shows the same circuit as shown in (a) with one component reversed.
State the reading on the voltmeter and explain your answer.
reading = ...............................................................
explanation .......................................................................................................................
...........................................................................................................................................
[2]
[Total: 4]