Which equation is used to define resistance?
energy = (current)2 × resistance × time
potential difference = current × resistance
power = (current)2 × resistance
resistivity = resistance × area ÷ length
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Syllabus Edition
First teaching 2020
Last exams 2024
Which equation is used to define resistance?
energy = (current)2 × resistance × time
potential difference = current × resistance
power = (current)2 × resistance
resistivity = resistance × area ÷ length
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What is the unit of resistance when expressed in SI base units?
kg m2 s–2 A–1
kg m2 s–3 A–2
kg m s–2 A–1
kg m s–3 A–1
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Which graph shows the I–V characteristic of a filament lamp ?
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The resistance R of a resistor is determined by measuring the potential difference V across it and the current I in it. The value of R is then calculated using the equation
The values measured are V = 1.00 ± 0.05 V and I = 0.50 ± 0.01 A.
What is the percentage uncertainty in the value of R ?
2.5 %
3.0 %
7.0 %
10.0 %
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The graph shows how the electric current I through a conducting liquid varies with the potential difference V across it.
At which point on the graph does the liquid have the smallest resistance?
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The graphs show the variation with potential difference V of the current I for three circuit components.
The components are a metal wire at constant temperature, a semiconductor diode and a filament lamp.
Which row of the table correctly identifies these graphs?
|
Metal wire at constant temperature |
Semiconductor diode |
Filament lamp |
A B C D |
X Y Y Z |
Z X Z X |
Y Z X Y |
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What is a correct statement of Ohm's Law?
the potential difference across a component equals the current providing the resistance and other physical conditions stay constant
the potential difference across a component equals the current multiplied by the resistance
the potential difference across a component is proportional to its resistance.
the potential difference across a component is proportional to the current in it providing physical conditions stay constant
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The graphs show possible current-voltage (I–V) relationships for a filament lamp and a semiconductor diode.
Which row best specifies the correct I–V graphs for the lamp and the diode?
|
Filament lamp |
Semiconductor diode |
A B C D |
P P Q Q |
R S R S |
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An electrical component has a potential difference V across it and a current I through it. A graph of I against V is drawn and is marked in three sections WX, XY and YZ.
In which ways does the resistance of the component vary within each of the three sections?
|
WX |
XY |
YZ |
A B C D |
constant constant increases increases |
decreases increases decreases increases |
increases increases constant decreases |
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The graph shows the variation with potential difference (p. d.) of the current in a lamp filament.
Which statement explains the shape of this graph?
as the filament temperature rises, electrons can pass more easily through the filament
it takes time for the filament to reach its working temperature
the power output of the filament is proportional to the square of the current in it
the resistance of the filament increases with a rise in temperature
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The graph shows how current I varies with voltage V for a filament lamp.
Since the graph is not a straight line, the resistance of the lamp varies with V.
Which row gives the correct resistance at the stated value of V?
|
V / V |
R / Ω |
A B C D |
2.0 4.0 6.0 8.0 |
1.5 3.2 1.9 0.9 |
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A charge of 8.0 C passes through a resistor of resistance 30 Ω at a constant rate in a time of 20 s.
What is the potential difference across the resistor?
0.40 V
5.3 V
12 V
75 V
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The I -V characteristics of two electrical components P and Q are shown below.
Which statement is correct ?
P is a resistor and Q is a filament lamp
the resistance of Q increases as the current in it increases
for a current of 1.9 A, the resistance of Q is approximately half that of P
for a current of 0.5 A, the power dissipated in Q is double that in P
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The resistance R of a resistor is to be determined. The current I in the resistor and the potential difference V across it are measured.
The results, with their uncertainties, are
I = (2.0 ± 0.2) A V = (15.0 ± 0.5) V
What is the uncertainty in this value for R ?
± 0.3 Ω
± 0.5 Ω
± 0.7 Ω
± 1 Ω
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The variation with potential difference V of the current I in a semiconductor diode is shown below.
What is the resistance of the diode for applied potential differences of +1.0 V and –1.0 V ?
|
Resistance |
|
at +1.0 V |
at –1.0 V |
|
A B C D |
20 Ω 20 Ω 0.05 Ω 0.05 Ω |
infinite zero infinite zero |
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A battery of negligible internal resistance is connected to two 10 Ω resistors in series.
What charge flows through each of the 10 Ω resistors in 1 minute?
0.30 C
0.60 C
3.0 C
18 C
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Two heating coils X and Y, of resistance RX and RY respectively, deliver the same power when 12 V is applied across X and 6 V is applied across Y.
What is the ratio ?
2
4
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A student found two unmarked resistors. To determine the resistance of the resistors, the circuit below was set up. The resistors were connected in turn between P and Q, noting the current readings.
The voltage readings were noted without the resistors and with each resistor in turn.
The results were entered into a spreadsheet, as shown.
1.5 |
1.3 |
28 |
46 |
1.5 |
1.4 |
14 |
100 |
The student forgot to enter the column headings.
Which order of the headings would be correct?
A |
|
||||
B |
|
||||
C |
|
||||
D |
|
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A 2 Ω resistor and a 4 Ω resistor are connected to a cell.
Which graph shows how the potential V varies with distance between X and Y ?
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The diagram shows a length of track from a model railway connected to a battery, a resistor and a relay coil.
With no train present, there is a current in the relay coil which operates a switch to turn on a light.
When a train occupies the section of track, most of the current flows through the wheels and axles of the train in preference to the relay coil. The switch in the relay turns off the light.
Why is a resistor placed between the battery and the track?
to limit the heating of the wheels of the train
to limit the energy lost in the relay coil when a train is present
to prevent a short circuit of the battery when a train is present
to protect the relay when a train is present
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The diagram shows an electric pump for a garden fountain connected by an 18 m cable to a 230 V mains electrical supply.
The performance of the pump is acceptable if the potential difference (p.d.) across it is at least 218 V. The current through it is then 0.83 A.
What is the maximum resistance per meter of each of the two wires in the cable if the pump is to perform acceptably?
0.40 Ω m–1
0.80 Ω m–1
1.3 Ω m–1
1.4 Ω m–1
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The graph below shows the variation of the current I through a lamp with potential difference V across it.
Which of the following graphs best represents the variation of power P dissipated in the same lamp with I 2 ?
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Circuit contains three identical lamps A, B and C. Circuit also contains three switches, S1, S2 and S3, as shown.
One of the lamps is faulty. In order to detect the fault, an ohm-meter is connected between terminals X and Y.
When measuring resistance, the ohm-meter causes negligible current in the circuit. Readings of the ohm-meter for different switch positions are shown in the table.
Switch |
Meter reading / Ω |
||
S1 |
S2 |
S3 |
|
open closed open open |
open open closed closed |
open open open closed |
∞ 15 30 15 |
Which lamps are faulty?
A & B
B only
B & C
C only
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The current flowing through a component varies with the potential difference V across it as shown.
Which graph best represents how the resistance R varies with V ?
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The circular cross-sectional area of a uniform metal wire varies along its length. There is a current in the wire. The narrow end of the wire is at a reference potential of zero.
Which graph best represents the variation with distance x along the wire of the potential difference V relative to the reference zero?
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The graph shows the I -V characteristics of a semiconductor diode
A cell of e. m .f. 1.2 V and negligible internal resistance is connected in series to a semiconductor diode and a resistor R1, as shown below
A resistor R2 of resistance 375 Ω is connected across the cell. The diode has the characteristic shown in the graph. The current supplied by the cell is 7.6 mA.
What is the resistance of R1?
82 Ω
114 Ω
160 Ω
260 Ω
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The graph shows how the current I varies with potential difference V for an electrical component.
Which row of the table gives the resistance of the component at V2 and describes how the resistance changes from V1 to V2 ?
|
Resistance at V2 |
Change in resistance from V1 to V2 |
A |
|
increases |
B |
|
decreases |
C |
|
increases |
D |
|
decreases |
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The graph shows the relationship between potential difference V and current I for a fixed 20 Ω resistor and a filament lamp.
The resistor and lamp are placed in series with a 9 V battery of negligible internal resistance. What is the current in the circuit ?
0.1 A
0.2 A
0.3 A
0.4 A
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The graphs show the I -V characteristics for a metal conductor and a thermistor
What is the ratio ?
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One style of light bulb, very different from the "incandescent" design which works on the principle of a super-heated wire filament emitting light, is called a gas discharge tube.
In this design of light bulb, light is produced by the direct excitation of gas molecules as electric current passes between two electrodes.
What will the I - V graphs of these bulbs look like?
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