# Topic 5 Electricity

Revision questions Topic 5: Set 1
Q1.
Which row shows the resistances of an ideal ammeter and an ideal voltmeter?
Ideal
ammeter
Ideal
voltmeter
A
infinite
infinite
B
infinite
zero
C
zero
infinite
D
zero
zero
(Total 1 mark)
Q2.
Which is equivalent to the ohm?
A J C–2 s–1
B J C–2 s
C Js
D J s–1
(Total 1 mark)
Q3.
A filament lamp with resistance 12 Ω is operated at a power of 36 W.
How much charge flows through the filament lamp during 15 minutes?
A
26 C
Hint: Charge/time = current
B
1.6 kC
Calculate current from first
statement
C
2.7 kC
D
6.5 kC
(Total 1 mark)
Page 1 of 22
Revision questions Topic 5: Set 1
Q4.
The graph shows the current–voltage (I–V) characteristics for two components.
The two components are connected in parallel with a 12 V battery that has negligible
internal resistance.
Hint:
What is the current in the battery?
Components in parallel
have the same voltage.
A 7.9 mA
B 14.5 mA
C 15.8 mA
D 23.0 mA
The currents through
the two components
to find the current in
each component.
Page 2 of 22
(Total 1 mark)
Revision questions Topic 5: Set 1
Q5.
In the circuit shown, a potential difference of 3.0 V is applied across XY.
What is the current in the 5 Ω resistor?
Hint: The 5 Ω and
3 Ω R’s are in
series. They have
the same current.
A 0.38 A
B 0.60 A
C 0.75 A
D 2.7 A
(Total 1 mark)
Q6.
The circuit shows a cell with negligible internal resistance connected in a circuit with three
resistors, an ammeter and a voltmeter.
Which row shows the readings on the ammeter and voltmeter?
Current / A
Voltage / V
A
0.075
0.75
B
0.075
1.50
C
0.150
0.75
D
0.150
1.50
Hint: voltmeter has a very
high resistance. Current
through the 20 Ω resistor
can be assumed to be
zero.
(Total 1 mark)
Page 3 of 22
Revision questions Topic 5: Set 1
Q7.
The table shows corresponding values of potential difference V and current I for four
electrical components A, B, C and D.
A
B
C
D
V/V
I/A
I/A
I/A
I/A
0
0.0
0.0
0.0
0.0
2
0.0
0.3
0.4
0.3
4
0.1
0.6
0.8
0.6
6
0.7
0.9
1.2
0.9
8
1.4
1.2
1.6
1.1
10
2.1
1.5
2.0
1.3
12
2.8
1.8
2.4
1.4
Which component is an ohmic conductor with the greatest resistance?
A
A
B
B
C
C
D
D
Ohmic: current is proportional
to V.
Check that V/I is the greatest
amongst the given values.
(Total 1 mark)
Page 4 of 22
Revision questions Topic 5: Set 1
Q8.
Two cylindrical wires P and Q are of equal length and made of the same material.
The diameter of P is greater than that of Q.
P and Q are connected in series and the ends of this arrangement are connected to a
power supply.
Which two quantities are the same for P and Q?
A
potential difference across wire
resistivity
B
resistivity
current
C
current
resistance
D
resistance
potential difference across wire
(Total 1 mark)
Q9.
Two resistors X and Y are connected in series with a power supply of emf 30 V and
negligible internal resistance.
The resistors are made from wire of the same material. The wires have the same length.
X uses wire of diameter d and Y uses wire of diameter 2d.
What is the reading on the voltmeter?
A
10 V
B
15 V
C
20 V
D
24 V
You need to know the ratio of
the resistances of the two
resistors.
Since they are in series, ratio of
the voltages between the two
resistors is the same.
(Total 1 mark)
Page 5 of 22
Revision questions Topic 5: Set 1
Q10.
A resistor of resistance R and three identical cells of emf E and internal resistance r are
connected as shown.
What is the current in the resistor?
EMF’s in parallel have an
effective voltage of E.
A
The internal resistance is
equal to three resistors
in parallel.
B
C
D
(Total 1 mark)
Q11.
Resistors of resistance R, R and 3R are connected as shown.
What is the resistance of the arrangement?
A
B
C
D
(Total 1 mark)
Page 6 of 22
Revision questions Topic 5: Set 1
Q12.
A circuit consists of a cell, a thermistor, a fixed resistor and two ammeters.
The cell has a constant electromotive force and negligible internal resistance. Readings
from the two ammeters are taken.
Which row describes what happens to the current in each ammeter when the temperature
of the thermistor decreases?
Current in ammeter A1
Current in ammeter A2
A
Decreases
Unchanged
B
Decreases
Increases
C
Increases
Decreases
D
Increases
Unchanged
Hint: Know the property of a
thermistor.
The current through one parallel
branch is not affected by the current
in the other parallel branch.
(Total 1 mark)
Q13.
Measurements are taken to determine the resistivity of a uniform metal wire. The
table shows the quantities measured and their percentage uncertainties.
Quantity
Percentage
uncertainty
potential difference across
wire
0.3%
current in wire
5.0%
diameter of wire
4.0%
length of wire
0.2%
What is the percentage uncertainty in the calculated value for the resistivity of the metal of
the wire?
A 1.6%
B 9.5%
C 13.5%
D 21.5%
(Total 1 mark)
Page 7 of 22
Revision questions Topic 5: Set 1
Q14.
Two identical batteries each of emf 1.5 V and internal resistance 1.6 Ω are connected in
parallel. A 2.4 Ω resistor is connected in parallel with this combination.
What is the current in the 2.4 Ω resistor?
A 0.38 A
B 0.47 A
C 0.75 A
Get the total R,
internal
resistance.
D 0.94 A
(Total 1 mark)
Q15.
The diagram shows the currents in a set of wires.
What is the magnitude of the current at X?
A zero
B 2A
C 3A
D 6A
(Total 1 mark)
Page 8 of 22
Revision questions Topic 5: Set 1
Q16.
Which graph shows how power dissipated P varies with current I in a component that
obeys Ohm’s law?
A
B
C
D
(Total 1 mark)
Q17.
In the circuit shown, the cell has an emf of 12 V and an internal resistance which is not
negligible.
When the resistance of the variable resistor is 10 Ω the voltmeter reads 10 V and the
The resistance of the variable resistor is changed to 5 Ω.
What is the new reading on the ammeter?
A 1.4 A
B 1.7 A
C 2.0 A
D 2.4 A
(Total 1 mark)
Page 9 of 22
Revision questions Topic 5: Set 1
Q18.
The diagram shows a temperature-sensing circuit.
The temperature of the thermistor is decreased.
Which row shows the changes to the ammeter reading and the voltmeter reading?
Ammeter
Voltmeter
A
increases
increases
B
increases
decreases
C
decreases
decreases
D
decreases
increases
(Total 1 mark)
Page 10 of 22
Revision questions Topic 5: Set 1
Magnetic field
Q19.
Which one of the following statements is correct?
An electron follows a circular path when it is moving at right angles to
A
a uniform magnetic field.
B
a uniform electric field.
C
uniform electric and magnetic fields which are perpendicular.
D
uniform electric and magnetic fields which are in opposite directions.
(Total 1 mark)
Q20.
Charged particles, each of mass m and charge Q, travel at a constant speed in a circle of
radius r in a uniform magnetic field strength B.
Which expression gives the frequency of rotation of a particle in the beam?
Hint: Apply the equation
A
Centripetal force = magnetic force on a charge
B
C
D
(Total 1 mark)
Q21.
Two electrons, X and Y, travel at right angles to a uniform magnetic field.
X experiences a magnetic force, FX, and Y experiences a magnetic force, FY.
What is the ratio
if the kinetic energy of X is half that of Y?
A
C
D
B
1
(Total 1 mark)
Page 11 of 22
Revision questions Topic 5: Set 1
Q22.
The path followed by an electron of momentum p, carrying charge –e, which enters a
magnetic field at right angles, is a circular arc of radius r.
What would be the radius of the circular arc followed by an α particle of momentum 2p,
carrying charge +2e, which entered the same field at right angles?
A
B
r
C
2r
D
4r
(Total 1 mark)
Q23.
When an electron is moving at a speed v perpendicular to a uniform magnetic field of flux
density B, it follows a path of radius R.
A second electron moves at a speed
density 4B.
perpendicular to a uniform magnetic field of flux
What is the radius of the path of the second electron?
A
B
C 2R
D 8R
(Total 1 mark)
Page 12 of 22
Revision questions Topic 5: Set 1
Q24.
Two charged particles, P1 and P2, follow circular paths as they move at right angles to the
same uniform magnetic field. Both particles are travelling at the same speed.
The radius of the path travelled by P1 is twice the radius of the path travelled by P2.
The mass of P1 is m and its charge is q.
What is the mass of P2 and the charge of P2?
Mass of P2
Charge of P2
A
2m
q
B
2m
2q
C
m
m
D
q
2q
(Total 1 mark)
Q25.
(a)
Figure 1 shows a negative ion which has a charge of –3e and is free to move in a
uniform electric field. When the ion is accelerated by the field through a distance of
63 mm parallel to the field lines its kinetic energy increases by 4.0 &times; 10–16 J.
Figure 1
(i)
State and explain the direction of the electrostatic force on the ion.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
Page 13 of 22
Revision questions Topic 5: Set 1
(ii)
Calculate the magnitude of the electrostatic force acting on the ion.
magnitude of electrostatic force ____________________ N
(2)
(iii)
Calculate the electric field strength.
electric field strength ____________________ NC–1
(1)
(b)
Figure 2 shows a section of a horizontal copper wire carrying a current of 0.38 A.
A horizontal uniform magnetic field of flux density B is applied at right angles to the
wire in the direction shown in the figure.
Figure 2
(i)
State the direction of the magnetic force that acts on the moving electrons in
the wire as a consequence of the current and explain how you arrive at your
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
Page 14 of 22
Revision questions Topic 5: Set 1
(ii)
Copper contains 8.4 &times; 1028 free electrons per cubic metre. The section of wire
in Figure 2 is 95 mm long and its cross-sectional area is 5.1 &times; 10–6 m2.
Show that there are about 4 &times; 1022 free electrons in this section of wire.
(1)
(iii)
With a current of 0.38 A, the average velocity of an electron in the wire is
5.5 &times; 10–6 m s–1 and the average magnetic force on one electron is 1.4 &times; 10–25
N.
Calculate the flux density B of the magnetic field.
flux density ____________________ T
(2)
(Total 10 marks)
Q26.
When travelling in a vacuum through a uniform magnetic field of flux density 0.43 m T, an
electron moves at constant speed in a horizontal circle of radius 74 mm, as shown in the
figure below.
(a)
When viewed from vertically above, the electron moves clockwise around the
horizontal circle. In which one of the six directions shown on the figure above,
+x, –x, +y, –y, +z or –z, is the magnetic field directed?
direction of magnetic field ______________________
(1)
Page 15 of 22
Revision questions Topic 5: Set 1
(b)
Explain why the electron is accelerating even though it is travelling at constant
speed.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
(c)
(i)
By considering the centripetal force acting on the electron, show that its speed
is 5.6 &times; 106 m s–1.
(2)
(ii)
Calculate the angular speed of the electron, giving an appropriate unit.
(2)
(iii)
How many times does the electron travel around the circle in one minute?
(2)
(Total 9 marks)
Page 16 of 22
Revision questions Topic 5: Set 1
Q27.
Different magnetic fields are present in the two chambers shown. A particle enters the first
chamber at a velocity of 80 m s–1 and is deflected into a circular path of radius 200 mm
In the second chamber it follows a circular path of radius 100 mm
The particle leaves the second chamber at a speed of
A 20 m s–1
B 40 m s–1
C 80 m s–1
D 160 m s–1
(Total 1 mark)
Page 17 of 22
Revision questions Topic 5: Set 1
Mark schemes
Q1.
C
[1]
Q2.
B
[1]
Q3.
B
[1]
Q4.
D
23.0 mA
[1]
Q5.
A
[1]
Q6.
B
[1]
Q7.
B
[1]
Q8.
B
[1]
Q9.
D
24 V
[1]
Q10.
Page 18 of 22
Revision questions Topic 5: Set 1
A
[1]
Q11.
A
[1]
Q12.
A
[1]
Q13.
C
13.5%
[1]
Q14.
B
0.47 A
[1]
Q15.
D
6A
[1]
Q16.
A
[1]
Q17.
B
1.7 A
[1]
Q18.
D
[1]
Q19.
A
Page 19 of 22
Revision questions Topic 5: Set 1
[1]
Q20.
A
[1]
Q21.
C
[1]
Q22.
B
[1]
Q23.
A
[1]
Q24.
D
[1]
Q25.
(a)
(i)
force acts towards left or in opposite direction to field lines ✓
because ion (or electron) has negative charge
(∴ experiences force in opposite direction to field) ✓
Mark sequentially.
Essential to refer to negative charge (or force on + charge is
to right) for 2nd mark.
2
(ii)
(use of W = F s gives) force F =
✓
= 6.3(5) &times; 10–15 (N) ✓
If mass of ion m is used correctly using algebra with F =
ma, allow both marks (since m will cancel). If numerical
value for m is used, max 1.
2
(iii)
= 1.3(2) ✓ 104 (N C-1) ✓
electric field strength
[or
(833 V)
Page 20 of 22
Revision questions Topic 5: Set 1
= 1.3(2) ✓ 104 (V m-1) ✓ ]
Allow ECF from wrong F value in (ii).
1
(b)
(i)
(vertically) downwards on diagram ✓
reference to Fleming’s LH rule or equivalent statement ✓
Mark sequentially.
1st point: allow “into the page”.
2
(ii)
number of free electrons in wire = A &times; l &times; number density
= 5.1 &times; 10–6 &times; 95 &times; 10–3 &times; 8.4 &times; 1028 = 4.1 (4.07) &times; 1022 ✓
Provided it is shown correctly to at least 2SF, final answer
alone is sufficient for the mark. (Otherwise working is
mandatory).
1
✓ = 0.16 (0.159) (T) ✓
(iii)
✓ = 0.16 (0.158) (T) ✓ ]
[or
In 2nd method allow ECF from wrong number value in (ii).
2
[10]
Q26.
(a)
magnetic field direction: −z (1)
1
(b)
direction changes meaning that velocity is not constant (1)
acceleration involves change in velocity
(or acceleration is rate of change of velocity) (1)
[alternatively
magnetic force on electron acts perpendicular to its velocity (1)
force changes direction of movement causing acceleration (1)]
2
(c)
(i)
BQv =
(1) gives v
(1) (= 5.59 &times; 106 m s−1)
2
Page 21 of 22
Revision questions Topic 5: Set 1
(ii)
angular speed ω
= 7.5(5) &times; 107 (1)
unit: rad s−1 (1) (accept s−1)
2
(iii)
frequency of electron’s orbit f
(= 1.20 &times; 107 s−1)
(1)
number of transits min−1 = 1.20 &times; 107 &times; 60 = 7.2 &times; 108 (1)
[alternatively
orbital period
[or
]
(= 8.32 &times; 10−8 s)
number of transits min−1 =
(1)]
2
[9]
Q27.
C
[1]
Page 22 of 22