Exam Review: Topic 05 – Electric currents
Practice Test: 30 marks (39 minutes)
Additional Problem: 25 marks (37 minutes)
1.
Reagan IB Physics
One electronvolt is equal to
A.
1.6 × 10–19 C.
B.
1.6 × 10–19 J.
C.
1.6 × 10–19 V.
D.
1.6 × 10–19 W.
(Total 1 mark)
2.
In the circuit below, which of the following will cause
the greatest increase in the reading of the voltmeter?
A.
An increase in temperature
B.
An increase in light intensity
C.
A decrease in temperature
D.
A decrease in light intensity
(Total 1 mark)
3.
The graph shows the I–V characteristics of two resistors.
When resistors X and Y are connected in series, the current in the resistors is 2.0 A. What is the
resistance of the series combination of X and Y?
A.
7.0 Ω
C.
1.1 Ω
B.
1.3 Ω
D.
0.14 Ω
(Total 1 mark)
1/10
Exam Review: Topic 05 – Electric currents
4.
Reagan IB Physics
A point charge of magnitude 2.0 µC is moved between two points X and Y. Point X is at a
potential of +6.0 V and point Y is at a potential of +9.0 V. The gain in potential energy of the
point charge is
A.
0.20 µJ.
B.
1.5 µJ.
C.
6.0 µJ.
D.
30 µJ.
(Total 1 mark)
5.
A resistor of resistance 12 Ω is connected in series with a cell of negligible internal resistance.
The power dissipated in the resistor is P. The resistor is replaced with a resistor of resistance
3.0 Ω. What is the power dissipated in this resistor?
A.
0.25 P
B.
P
C.
2.0 P
D.
4.0 P
(Total 1 mark)
6.
A copper wire, of electric resistance R, has a length L and a cross-section area S. Another
S
copper wire has a length 2L and a cross-section area of . Which of the following is the
2
resistance of this wire?
A.
R
4
B.
R
2
C.
2R
D.
4R
(Total 1 mark)
7.
The electromotive force (emf) of a cell is defined as
A.
the power supplied by the cell per unit current from the cell.
B.
the force that the cell provides to drive electrons round a circuit.
C.
the energy supplied by the cell per unit current from the cell.
D.
the potential difference across the terminals of the cell.
(Total 1 mark)
2/10
Exam Review: Topic 05 – Electric currents
8.
Reagan IB Physics
The circuit shows a resistor R connected in series with a battery and a resistor of resistance 10
Ω. The emf of the battery is 20 V and it has negligible internal resistance. The current in the
circuit is 1.0 A.
Which of the following is the resistance of R?
A.
1.0 Ω
B.
2.0 Ω
C.
10 Ω
D.
20 Ω
(Total 1 mark)
9.
In the circuit below, the battery has negligible internal resistance. Three identical lamps L, M
and N of constant resistance are connected as shown.
The filament of lamp N breaks. Which of the following shows the subsequent changes to the
brightness of lamp L and lamp M?
Lamp L
Lamp M
A.
stays the same
decreases
B.
increases
stays the same
C.
increases
decreases
D.
decreases
increases
(Total 1 mark)
10.
Which of the following correctly gives the resistance of an ideal ammeter and resistance of an
ideal voltmeter?
Ammeter
Voltmeter
A.
infinite
infinite
B.
zero
zero
C.
zero
infinite
D.
infinite
zero
(Total 1 mark)
3/10
Exam Review: Topic 05 – Electric currents
11.
Reagan IB Physics
In the circuits below the cells have the same emf and zero internal resistance. The resistors all
have the same resistance.
Which of the following gives the ratio
A.
1
4
B.
1
2
power dissipated in X
?
power dissipated in Y
C.
2
D.
4
(Total 1 mark)
12.
A cell of emf ε and internal resistance r delivers current to a small electric motor.
450 C of charge flows through the motor and 9000 J of energy are converted in the motor. 1800
J are dissipated in the cell. The emf of the cell is
A.
4.0 V.
B.
16 V.
C.
20 V.
D.
24 V.
(Total 1 mark)
13.
This question is about electrical resistance and electric circuits.
(a)
Define resistance and state Ohm’s law.
Resistance: ...................................................................................................................
......................................................................................................................................
Ohm’s law: ..................................................................................................................
......................................................................................................................................
(2)
4/10
Exam Review: Topic 05 – Electric currents
(b)
Reagan IB Physics
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.
......................................................................................................................................
......................................................................................................................................
(2)
(c)
The manufacturer of the resistor in (b) 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.
......................................................................................................................................
......................................................................................................................................
(2)
(d)
The resistance of each of the resistors in the circuit below is measured to be 1.5 Ω with
an accuracy of ±10 %.
The cell has an emf of 2.0 V and negligible internal resistance.
(i)
Define emf.
...........................................................................................................................
...........................................................................................................................
(1)
(ii)
Determine the minimum and the maximum power that could be dissipated in this
circuit.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(3)
(Total 10 marks)
5/10
Exam Review: Topic 05 – Electric currents
14.
(a)
Reagan IB Physics
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)
(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.
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
(2)
6/10
Exam Review: Topic 05 – Electric currents
(c)
Reagan IB Physics
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.
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
(3)
(Total 8 marks)
Additional Problems
15.
In the circuit shown below, the cell has negligible internal resistance.
Which of the following equations is correct?
A.
I1 = 2I2
B.
I1 = 2I3
C.
I2 = 2I3
D.
I3 = 2I1
(Total 1 mark)
16.
In the circuit below, the voltmeter has a resistance 100 kΩ. The battery has negligible internal
resistance and emf 6 V.
The reading on the voltmeter is
A.
0 V.
B.
2 V.
C.
3 V.
D.
4 V.
(Total 1 mark)
7/10
Exam Review: Topic 05 – Electric currents
17.
Reagan IB Physics
This question is about electric fields and electric circuits.
(a)
Two parallel, charged metal plates A and B are in a vacuum.
At a particular instant an electron is at point P.
On the diagram, draw
(i)
the electric field pattern due to the plates.
(3)
(ii)
an arrow to represent the direction of the force on the electron at P.
(1)
(b)
The acceleration of the electron at P is 8.8 × 1014 m s–2. Determine the magnitude of the
electric field strength at the point P.
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
(3)
(c)
The electric potential energy of the electron changes by 1.9 × 10–17 J as it moves from
one plate to the other. Show that the potential difference between the plates is 120 V.
......................................................................................................................................
......................................................................................................................................
(1)
8/10
Exam Review: Topic 05 – Electric currents
(d)
Reagan IB Physics
A resistor R and a filament lamp L are connected in series with a battery. The battery has
an emf of 12 V and internal resistance 4.0 Ω. The potential difference across the filament
of the lamp is 3.0 V and the current in the filament is 0.25 A.
(i)
Define emf and describe the concept of internal resistance.
emf:
...........................................................................................................................
Internal resistance:
...........................................................................................................................
(2)
(ii)
Calculate the total power supplied by the battery.
...........................................................................................................................
...........................................................................................................................
(1)
(iii) Calculate the power dissipated in the external circuit.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(iv)
Determine the resistance of the resistor R.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(3)
9/10
Exam Review: Topic 05 – Electric currents
18.
Reagan IB Physics
(Total 16 marks)
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 kΩ. The maximum resistance of the
variable resistor is 15Ω.
(a)
Explain, without doing any calculations, whether there is a position of the slide S at
which the lamp will be lit.
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
(3)
(b)
Estimate the maximum reading of the ammeter.
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
(2)
(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)
10/10
Exam Review: Topic 05 – Electric currents
Reagan IB Physics
Mark Scheme
1.
B
3.
A
5.
D
7.
A
9.
C
11.
D
2.
B
4.
C
6.
D
8.
C
10.
C
12.
D
13.
(a)
resistance:
Ohm’s law:
(b)
(c)
(d)
(a)
(b)
2
RA
;
l
⎛ 1.5 × π × 1.2 2 × 10 −6 ⎞
= ⎜
= ⎟⎟ 3.1 × l0–4 Ωm;
−2
⎜
2.2 × 10
⎝
⎠
ρ=
2
⎛ P ⎞ 1
= ⎟
I = ⎜⎜
;
⎟
⎝ R ⎠ 1.35
= 0.86 A;
(i)
(ii)
14.
the ratio of potential difference across a device/load/
resistor to current in the device/load/resistor;
the resistance of a conductor is constant provided
its temperature is constant / the current is proportional
to the voltage across;
2
the power supplied per unit current / work done per unit
charge in moving charge completely round the circuit /
energy per unit charge made available by the source;
1
minimum resistance is 2.0 Ω, maximum resistance is 2.5 Ω;
⎛ 2.0 2 ⎞
⎟
so maximum power is ⎜
⎜ 2.0 ⎟ = 2.0 W
⎝
⎠
2
⎛ 2.0 ⎞
⎟
and minimum power is ⎜
⎜ 2.5 ⎟ = 1.6 W;
⎝
⎠
voltmeter in parallel across X;
ammeter in series with X;
correct circuit;
(allow ecf from 1st and 2nd marking points) Accept voltmeter
connections that include ammeter (in series with X) Condone
re-drawing of resistor X closer to variable resistor.
I = 2.4 A at 2.0 V;
2
;
2 .4
= 0.83 Ω
Award [1 max] for use of gradient of graph from (2,2.4) to origin.
3
[10]
3
2
11/10
Exam Review: Topic 05 – Electric currents
(c)
Reagan IB Physics
total p.d. across 1 Ω resistor = 1.3(V);
p.d. across X = 0.7(V);
reading from graph I = 1.3 A at 0.7 V / evidence that the graph has been read;
Award [1 max] if value of calculated p.d. is incorrect but there is
clear graphical evidence of derivation of current (typically marks
on graph).
or
total p.d. across X + resistor = 2.0 (V);
this occurs when VX = 0.7(V) and V1.0 = 1.3(V);
at I = 1.3 A;
2
[8]
15.
C
[1]
16.
B
[1]
17.
(a)
(i)
(ii)
(b)
uniform field equal spacing of lines;
edge effect;
direction;
3
as shown;
1
combine F = qE and F = ma;
ma
to get E =
;
q
E = 5.0 × 103 N C–1/V m–1;
(c)
(d)
V=
1.9 × 10 −17
1.6 × 10 −19
= 120 V
3
;
1
(i)
3.0 W;
1
(ii)
power dissipated in battery = (0.252 × 4.0) = 0.25 W;
power dissipated in circuit = (3.0 – 0.25) = 2.8 (2.75) W;
2
12/10
Exam Review: Topic 05 – Electric currents
(iii)
Reagan IB Physics
power dissipated in lamp = (3.0 × 0.25) = 0.75 W;
power dissipated in resistor = (2.75 – 0.75) = 2.0 W;
2.0 ⎞
⎛
resistance ⎜ =
⎟ = 32 Ω;
⎝ 0.25 2 ⎠
3
or
resistance of lamp =12 Ω;
12 = 0.25 (R + 16);
R = 32 Ω;
or
V across R = 8.0V;
0 .8
R=
;
0.25
= 32 Ω;
3
[16]
18.
(a)
there are no positions;
the lamp is effectively in series with 100 kΩ no matter what the position of S;
this means that the pd across it will always be close to zero (very small) / never
reach 6 V;
or
the resistance of the filament is much smaller than 100 kΩ;
so (nearly) all the potential of the battery appears across the variable resistance;
Award [0] for incorrect argument or just the answer without any explanation.
(b)
I=
=
3
V
;
R
12
=1.2 ×10 −4 A ;
5
10
2
(c)
correct position of ammeter;
correct position of voltmeter (either to the right or left of the lamp);
2
[7]
13/10