1
1
A 12V battery is connected in series to a 24 W lamp and to a parallel pair of identical resistors X
and Y. The diagram shows the circuit.
The 24 W lamp lights at normal brightness when the potential difference (p.d.) across it is 6.0 V.
The lamp is at normal brightness.
(a) Calculate the resistance of the lamp.
resistance = ................................................. [3]
(b) Determine
(i)
the p.d. between A and B,
p.d. = ...................................................... [1]
(ii) the combined resistance of the parallel pair of identical resistors X and Y,
resistance = ........................................... [1]
(iii) the resistance of X.
resistance = ........................................... [2]
2
(c) Resistor X is removed from the circuit in the diagram.
Explain why the lamp becomes dimmer.
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[2]
[Total: 9]
2
The diagram shows three identical lamps and an ammeter connected to a power supply.
The switches are closed. Each lamp is rated at 60 W and operates at its normal working voltage of
110 V.
(a) Calculate:
(i)
the current in each lamp
current = ..............................................
[2]
current = ..............................................
[1]
(ii) the current in the ammeter
3
(iii) the voltage of the power supply.
voltage = ..............................................
(b)
(i)
[1]
Calculate the resistance of the filament of one of the lamps when working normally.
resistance = .............................................. [2]
(ii) Another lamp X has a filament with twice the resistance of each lamp in the circuit in
the diagram. The material and the temperature of the filament in lamp X is the same
as the filaments in the lamps in the diagram.
In the table, tick any box in the right-hand column that shows a possible difference
between the filament of lamp X and a filament of one of the lamps in the circuit.
X has half the length
X has twice the length
X has one quarter the area of cross-section
X has half the area of cross-section
X has two times the area of cross-section
X has four times the area of cross-section
[2]
[Total: 8]
3
The diagram shows a circuit with three 1.5 V cells.
4
(a) Calculate
(i)
the total electromotive force (e.m.f.) of the cells,
e.m.f. = ................................................... [1]
(ii) the total resistance of the circuit,
resistance = .................................................. [3]
(iii) the current in the 3.0 Ω resistor
current = ................................................ [2]
(b) State, using the letters in the diagram, how you would connect
(i)
an ammeter to measure the total current in the circuit,
................................................................................................................................
................................................................................................................................
[1]
(ii) a voltmeter to measure the potential difference (p.d.) across the 6.0 Ω resistor.
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................................................................................................................................
[1]
[Total: 8]
4
The diagram shows a horizontal wire PQ placed in the gap between the N pole and the S pole of
a magnet.
5
There is a current in the wire in the direction P to Q.
A force acts on the current-carrying wire in the magnetic field.
(a) On the diagram, draw
(i)
an arrow, labelled M to show the direction of the magnetic field in the gap between the
poles of the magnet,
[1]
(ii) an arrow, labelled F to show the direction of the force on the current-carrying wire due
to the magnetic field of the magnet.
[1]
(b) State the effect of reversing the direction of the current in wire PQ.
...........................................................................................................................................
[1]
(c) The magnet is removed and the horizontal, current-carrying wire is left on its own, as shown
in the diagram.
(i)
On the diagram, sketch the pattern of the magnetic field due to the current in the wire.
Indicate the field direction.
[3]
(ii) The current in PQ is increased.
State the effect of this change in current on the magnetic field.
................................................................................................................................
[1]
(d) A small magnet is placed at a point where the magnetic field is vertically upwards. State the
direction of the force on the S pole of the small magnet.
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...........................................................................................................................................
[1]
[Total: 8]
6
5
The diagram shows a 12 V power supply connected in a circuit.
The circuit includes a lamp and a resistance wire AB of constant cross-sectional area. There is a
sliding contact that can be moved between A and B.
(a) The rating of the lamp at normal brightness is 6.0 V, 9.0 W.
(i)
Calculate the current in the lamp at normal brightness.
current = ............................................... [2]
(ii) Calculate the resistance of the lamp at normal brightness.
resistance = ........................................... [2]
(b) AB is 1.00 m long and has a resistance of 5.0 Ω. The lamp has normal brightness when the
sliding contact is at X.
7
(i)
The sliding contact is moved to B.
Explain, without a calculation, why the lamp becomes dimmer.
................................................................................................................................
................................................................................................................................
................................................................................................................................
[1]
(ii) Calculate the distance AX for the lamp to have normal brightness.
distance AX = ........................................ [3]
[Total: 8]
6
The diagram shows a transformer that consists of two coils P and Q, and an iron core.
There are 200 turns on coil P and 340 turns on coil Q.
A 4.0 V a.c. power supply is connected to coil P.
8
(a)
(i)
Explain why there is a voltage between the two terminals of coil Q.
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................................................................................................................................
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................................................................................................................................
(ii) Explain why the core of the transformer is made of soft iron.
[3]
................................................................................................................................
................................................................................................................................
(b)
(i)
[1]
Calculate the voltage between the two terminals of coil Q.
voltage = ................................................ [2]
(ii) A heater is connected to coil Q. The current in the heater is 3.5 A. The transformer is
100% efficient.
Calculate the current in coil P.
current = ................................................ [2]
[Total: 8]
7
The diagram shows a source E of e.m.f. 60 V in a circuit.
9
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]
8
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.
10
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]
(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]
9
The figure shows a transformer used to allow lamps of different voltage ratings to be operated from
a 240 V mains supply.
11
P
W
240 V
primary coil
500 turns
X
Y
Z
secondary coil
500 turns
The primary coil and the secondary coil both have 500 uniformly-wound turns.
Electrical connections to the secondary coil can be made at four places, W, X, Y and Z.
(a) A lamp, designed to light at normal brightness with a 120 V supply, lights normally when
connected between W and X.
Calculate the number of turns between W and X.
number of turns = ...........................
[3]
(b) The lamp in (a) is connected between X and Y.
Describe and explain what happens to the lamp.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
[3]
(c) State what would happen if the 120 V lamp in (a) is connected between W and Z.
...........................................................................................................................................
...........................................................................................................................................
[1]
12
[Total: 7]
10 A battery consists of four cells, each of e.m.f. 1.2 V, in series.
(a) Calculate the e.m.f. of the battery.
e.m.f. = ........................................... [1]
(b) The battery is connected in a circuit with four 12 Ω resistors as shown in the circuit diagram.
V
Calculate the total resistance of this arrangement of resistors.
resistance = ......................................... [3]
(c) Calculate the reading on the voltmeter in the circuit diagram.
reading = ........................................ [2]
[Total: 6]
13
11
The diagram shows the same bar magnets with a coil of wire between them.
direction of
rotation
N
handle
S
galvanometer
A
(a) The coil of wire is rotated in the direction shown in the diagram.
On the diagram, draw an arrow to show the direction of the current in the coil. Explain your
answer.
...........................................................................................................................................
...........................................................................................................................................
[2]
(b) Explain how rotating the coil in the diagram continuously causes the galvanometer needle to
show an alternating current.
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[4]
[Total: 6]
12 A radio is connected to the mains supply using a step-down transformer
(a) Draw a labelled diagram of the structure of a basic step-down transformer.
[3]
14
(b) Explain the operation of a basic transformer.
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...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
[3]
[Total: 6]
13 A student fits an electrical generator to a bicycle.
When the front wheel turns, a magnet rotates between two coils of wire.
A lamp is connected to the coils of wire. When the magnet is rotating, the lamp is lit.
The diagram shows the magnet, the coils of wire and the lamp.
(a) Describe and explain how rotating the magnet causes the lamp to light.
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...........................................................................................................................................
...........................................................................................................................................
[3]
15
(b) State three ways of increasing the brightness of the bicycle lamp.
1. .......................................................................................................................................
2. .......................................................................................................................................
3. .......................................................................................................................................
[3]
[Total: 6]
14 The diagram shows an electric door lock.
The slot in the door contains an unmagnetised iron bolt attached to a spring.
The slot in the door frame is empty. This slot is surrounded by the coils of a solenoid.
In the diagram the door is unlocked. The spring is not stretched.
In the following diagram the door is locked. The spring is now stretched.
The bolt is initially in the position shown in the first diagram.
Describe and explain what happens when
16
(a) the switch S is closed,
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...........................................................................................................................................
[4]
(b) the switch S is reopened.
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...........................................................................................................................................
[2]
[Total: 6]
15 A bar magnet is made of metal.
(a) Suggest a metal from which the bar magnet is made.
...........................................................................................................................................
[1]
(b) The diagram shows the bar magnet being inserted into a coil of wire. The N-pole and the S-pole
of the bar magnet are marked.
The coil is connected to a galvanometer.
(i)
Explain why the galvanometer deflects as the bar magnet is being inserted into the coil.
................................................................................................................................
................................................................................................................................
................................................................................................................................
................................................................................................................................
[3]
17
(ii) Explain what determines the direction of the reading on the galvanometer.
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................................................................................................................................
................................................................................................................................
[2]
[Total: 6]