1.
This question is about electric circuits.
(a)
Define
(i)
electromotive force (emf ) of a battery.
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(1)
(ii)
electrical resistance of a conductor.
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(1)
(b)
A battery of emf ε and negligible internal resistance is connected in series to two
resistors. The current in the circuit is I.
(i)
State an equation giving the total power delivered by the battery.
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(1)
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(ii)
The potential difference across resistor R1 is V1 and that across resistor R2 is V2.
Using the law of the conservation of energy, deduce the equation below.
ε = V1 + V2
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(2)
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(c)
The graph shows the I-V characteristics of two conductors, X and Y.
On the axes below, sketch graphs to show the variation with potential difference V of the
resistance of conductor X (label this graph X) and conductor Y (label this graph Y).
You do not need to put any numbers on the vertical axis.
(3)
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(d)
The conductors in (c) are connected in series to a battery of emf ε and negligible internal
resistance.
The power dissipated in each of the two resistors is the same.
Using the graph given in (c),
(i)
determine the emf of the battery.
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(2)
(ii)
calculate the total power dissipated in the circuit.
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(2)
(Total 12 marks)
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2.
This question is about electrical resistance.
(a)
A resistor of resistance 1.5 Ω is made from copper wire of radius 0.18 mm. The resistivity
of copper is 1.7 × 10–8 Ω m. Determine the length of copper wire used to make the
resistor.
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(2)
(b)
The manufacturer of the resistor in (a) guarantees that the resistance is within 10 % of 1.5
Ω , provided that the power dissipation in the resistor does not exceed 1.0 W.
(i)
Suggest why the resistance of the resistor might be greater than 1.65 Ω if the power
dissipation in the resistor is greater than 1.0 W.
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(2)
(ii)
Show that, for a power dissipation of 1.0 W, the current in a resistor of resistance
1.5 Ω is 0.82 A.
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(1)
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(iii)
The 1.5 Ω resistor is connected in series with a variable resistor and battery of emf
6.0 V and internal resistance 1.8 Ω.
Estimate the resistance R of the variable resistor that will limit the current to
0.82 A.
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(3)
(Total 8 marks)
3.
This question is about electric circuits.
The components shown below are to be connected in a circuit to investigate how the current I in
a tungsten filament lamp varies with the potential difference V across it.
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(a)
Construct a circuit diagram to show how these components should be connected together
in order to obtain as large a range as possible for values of potential difference across the
lamp.
(4)
(b)
On the axes, sketch a graph of I against V for a filament lamp in the range V = 0 to its
normal working voltage.
(2)
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(c)
The lamp is marked with the symbols “1.25 V, 300 mW”. Calculate the current in the
filament when it is working normally.
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(1)
(d)
The resistivity of tungsten at the lamp’s working temperature is 4 × 10–7 Ωm. The total
length of the tungsten filament is 0.80 m. Estimate the radius of the filament.
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(4)
(e)
The cell is connected to two identical lamps connected in parallel. The lamps are rated at
1.25 V, 300 mW. The cell has an emf of 1.5 V and an internal resistance of 1.2 Ω.
Determine whether the lamps will light normally.
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(4)
(Total 15 marks)
4.
This question is about electric fields and electrical resistance.
(a)
State, in terms of electrons, the difference between a conductor and an insulator.
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(1)
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(b)
Suggest why there must be an electric field inside a current-carrying conductor.
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(3)
(c)
The magnitude of the electric field strength inside a conductor is 55 N C–1. Calculate the
force on a free electron in the conductor.
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(1)
(d)
Define resistance.
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(1)
(e)
A resistor made from a metal oxide has a resistance of 1.5 Ω. The resistor is in the form
of a cylinder of length 2.2 × 10–2 m and radius 1.2 × 10–3 m. Calculate the resistivity of
the metal oxide.
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(2)
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(f)
The manufacturer of the resistor in (e) guarantees its resistance to be within ±10 % of
1.5 Ω provided the power dissipation in the resistor does not exceed 1.0 W. Calculate the
maximum current in the resistor for the power dissipation to be equal to 1.0 W.
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(2)
(g)
Three of the resistors in (f) are connected in the circuit below.
The cell has an emf of 2.0 V and negligible internal resistance.
(i)
Define emf.
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(1)
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(ii)
Determine the minimum and the maximum power that could be dissipated in this
circuit.
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(3)
(Total 14 marks)
5.
(a)
Draw the complete diagram of the circuit that uses a potential divider, ammeter, voltmeter
and cell to measure the current-voltage characteristics for component X.
(3)
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(b)
The graph shows the current-voltage characteristics for the component X.
Component X is now connected across the terminals of a cell of emf 2.0 V and negligible
internal resistance. Use the graph to show that the resistance of X is 0.83 Ω.
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(2)
(c)
A resistor of constant resistance 1.0 Ω is connected in series with the cell in (b) and with
X. Use the graph to deduce that the current in the circuit is 1.3 A.
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(3)
(Total 8 marks)
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6.
This question is about electrical resistance.
(a)
A heating coil is to be made of wire of diameter 3.5 × 10–4 m. The heater is to dissipate
980 W when connected to a 230 V d.c. supply. The material of the wire has resistivity
1.3 × 10–6 Ω m at the working temperature of the heater.
(i)
Define electrical resistance.
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(1)
(ii)
Calculate the resistance of the heating coil at its normal working temperature.
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(2)
(iii)
Show that the length of wire needed to make the heating coil is approximately 4 m.
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(2)
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(b)
Three identical electrical heaters each provide power P when connected separately to a
supply S which has zero internal resistance. On the diagram below, complete the circuit
by drawing two switches so that the power provided by the heaters may be either P or 2P
or 3P.
(2)
(Total 7 marks)
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7.
This question is about an electric circuit.
A particular filament lamp is rated at 12 V, 6.0 mA. It just lights when the potential difference
across the filament is 6.0 V.
A student sets up an electric circuit to measure the I-V characteristic of the filament lamp.
In the circuit, shown below, the student has connected the voltmeter and the ammeter into the
circuit incorrectly.
The battery has emf 12 V and negligible internal resistance. The ammeter has negligible
resistance and the resistance of the voltmeter is 100 k. The maximum resistance of the
variable resistor is 15.
(a)
Explain, without doing any calculations, whether there is a position of the slide S at
which the lamp will be lit.
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(3)
(b)
Estimate the maximum reading of the ammeter.
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(2)
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(c)
Complete the circuit diagram below showing the correct position of the voltmeter and of
the ammeter in order to determine the I-V characteristic of the filament lamp.
(2)
(Total 7 marks)
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