Handout Ohm’s Law Questions – Topic 5 Electric Currents
1. A cell of emf E and internal resistance r is connected to a variable resistor. A voltmeter is
connected so as to measure the potential difference across the terminals of the cell. Which
one of the following is the correct circuit diagram of the arrangement?
A.
B.
E
r
E
r
V
V
C.
r
E
V
D.
r
E
V
1
2. The variation with potential difference V of the current I in an electric lamp is shown below.
I
Ip
0
0
P
Vp
V
At point P, the current is Ip, the potential difference is Vp and the gradient of the tangent to
the curve is G. What is the resistance of the lamp at point P?
A.
1
G
B.
G
C.
D.
Ip
Vp
Vp
Ip
2
3. Which one of the following shows a correct circuit, using ideal voltmeters and ammeters, for
measuring the I-V characteristic of a filament lamp?
A.
B.
A
A
V
C.
V
D.
A
A
V
V
(1)
3
5. In the circuit below, which meter is not correctly connected?
A
1
3
V
2
A
4
V
A.
1
B.
2
C.
3
D.
4
6. A battery is connected in series with a resistor R. The battery transfers 2 000 C of charge
completely round the circuit. During this process, 2 500 J of energy is dissipated in the
resistor R and 1 500 J is expended in the battery.
The emf of the battery is
A.
2.00 V.
B.
1.25 V.
C.
0.75 V.
D.
0.50 V.
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7. This question is about a filament lamp.
(a)
On the axes below, draw a sketch-graph to show the variation with potential difference
V of the current I in a typical filament lamp (the I–V characteristic). (Note: this is a
sketch-graph; you do not need to add any values to the axes).
V
0
(b)
(i)
0
I
Explain how the resistance of the filament is determined from the graph.
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(ii)
Explain whether the graph you have sketched indicates ohmic behaviour
or non-ohmic behaviour.
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A filament lamp operates at maximum brightness when connected to a 6.0 V supply. At
maximum brightness, the current in the filament is 120 mA.
(c)
(i)
Calculate the resistance of the filament when it is operating at maximum
brightness.
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(ii)
You have available a 24 V supply and a collection of resistors of a suitable
power rating and with different values of resistance. Calculate the resistance of
the resistor that is required to be connected in series with the supply such that
the voltage across the filament lamp will be 6.0 V.
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