A LevelPhysicsCIEExam Questions20. Magnetic Fields20.1 Magnetic Fields

Syllabus Edition

First teaching 2020

Last exams 2024

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Magnetic Fields (CIE A Level Physics)

Exam Questions

1 hour6 questions
Easy
Medium
1a
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A long straight wire passes through a piece of card. There is a current in the wire, as shown in Fig. 1.1a.

20-1-1a-e-20-1--e-magnetic-field-around-a-wire-1-cie-ial-sq

Fig. 1.1a

The current in the wire produces a magnetic field around the wire.

(i)
Fig. 1.1b shows the view of the card from above. On Fig. 1.1b, draw the magnetic field around the wire.
 
Show the direction of the magnetic field by drawing an arrow on each field line.
 

20-1-1a-e-magnetic-field-around-a-wire-2-cie-ial-sq

Fig. 1.1b

[2]

(ii)
Two identical wires with the same current pass through a different piece of card.
 
On Fig. 1.1c, draw the magnetic field around the wires.
 

20-1-1a-e-magnetic-field-around-two-wires-cie-ial-sq

Fig. 1.1c

[2]

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1b
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The current-carrying wire is placed in a uniform magnetic field. 

(i)
State the equation, and define all the variables, for the force on a current-carrying wire in a uniform magnetic field at different angles.
[2]
(ii)
Describe how the wire should be placed to experience 
1.  the maximum force due to the magnetic field
2.  no force due to the magnetic field.
[2]

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1c
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A current-carrying conductor placed at right angles to a uniform magnetic field which has a magnetic flux density of 15 × 10−3 T.

The conductor has a length of 1.2 m and a current of 1.5 A flowing through it.

Calculate the magnetic force acting on the conductor.

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1d
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The conductor is then rotated so that it is at an angle of 30° to the magnetic field.

Calculate the new force acting on the conductor.

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2a
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When the force, the magnetic field and the current are all mutually perpendicular to each other, the directions of each can be represented by Fleming’s left–hand rule, as shown in Fig. 1.1.

q2a-figure-1

Fig. 1.1

State what is represented by the direction of

 
(i)
the thumb
[1]
(ii)
the first finger
[1]
(iii)
the second finger
[1]

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2b
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Fig. 1.2 shows a magnetic field.

q2b-figure-2

Fig. 1.2

(i)
State whether the magnetic field is acting into or out of the page.
[1]
(ii)
An electron enters the magnetic field at point A, as shown in Fig. 1.3.
 
On Fig. 1.3, draw
 
1.  an arrow on the electron to show the direction of the force
2.  the path of the electron through the magnetic field
 

q4b-figure-1

Fig. 1.3

[4]

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2c
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When a moving charge enters a magnetic field the magnetic field produces a force on the charge, which can be calculated using

F space equals space B q v

(i)
State the meaning of the quantities B, q and v.
[3]
(ii)
When in the field, the charge begins to move in a circular orbit.
 
State the name and equation of the force that causes the charge to move in a circular orbit. 
[3]

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2d
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When the electron enters the magnetic field, its speed is 3.0 × 106 m s–1. The magnetic field has a magnetic flux density of 3.2 × 10–3 T.

(i)
Using the equations in (c), show that the radius of the circular orbit of the charged object inside the magnetic field is equal to
 

r space equals space fraction numerator m v over denominator B q end fraction

[3]

(ii)
Calculate the radius of the circular orbit of the electron
 
Mass of an electron = 9.11 × 10–31 kg
Charge of an electron = 1.60 × 10–19 C
[2]

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3a
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Positive charges are seen passing through different magnetic fields. 

In Table 1.1, state the direction of the missing quantity between B, v and F in each scenario
 

Table 1.1
q3a_magnetic-effects-of-electric-currents_ib-sl-physics-sq-medium

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3b
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Fig. 1.1 shows a rectangular wire loop ABCD with width 6.0 cm and length 9.0 cm in a uniform magnetic field of strength 0.75 T.

The current in the loop is 3.5 A.

20-1-3b-e-20-1-e-rectangular-loop-in-b-field-cie-ial-sq-correct

Fig. 1.1

Draw arrows on Fig. 1.1 to show the direction of the force on

 
(i)
side AB
[1]
(ii)
side CD
[1]

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3c
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Calculate the magnitude of the force acting on 

(i)
side AB
[2]
(ii)
side BC
[1]

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3d
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(i)
When the current is switched off the loop does not move.
 
Describe the motion of the loop once the current is switched on.
[1]
(ii)
Determine the effect on the magnitude of the magnetic force on side CD if
 
1.  the magnetic flux density is halved
2.  the length of the wire is increased by a factor of 4
3.  the current is reduced by 20%
[3]

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1
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A circular coil P carrying an alternating current produces a changing magnetic field. When a second similar coil Q is placed with its centre a distance x from the centre of coil P, as shown in Fig. 1.1, an electromotive force (e.m.f.) E is induced in coil Q.

q1-paper-5-specimen-2022-cie-ial-physics

Fig. 1.1

It is suggested that E is related to x by the relationship

E equals I Z e to the power of negative k x end exponent

where I is the current in coil P, and k and Z are constants.

Plan a laboratory experiment to test the relationship between E and x.

Draw a diagram showing the arrangement of your equipment.

Explain how the results could be used to determine values for k and Z.

In your plan you should include:

•    the procedure to be followed

•    the measurements to be taken

•    the control of variables

•    the analysis of the data

•    any safety precautions to be taken.

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2a
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A thin slice of conducting material has its faces PQRS and VWXY normal to a uniform magnetic field of flux density B, as shown in Fig. 6.1.

q6-paper-4-specimen-2022-cie-ial-physics

Fig. 6.1

Electrons enter the slice at right angles to face SRXY.

A potential difference, the Hall voltage VH, is produced between two faces of the slice.

(i)
Use letters from Fig. 6.1 to identify the two faces between which the Hall voltage is produced.

.......................................... and .......................................... [1]

(ii)
State and explain which of the two faces named in (a)(i) is the more positive.

[2]

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2b
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The Hall voltage VH is given by the expression

            begin mathsize 16px style V subscript H equals fraction numerator B I over denominator n t q end fraction end style

(i)
Use the letters in Fig. 6.1 to identify the distance t.

[1]

(ii)
The negative charge carriers (electrons) are replaced by positive charge carriers moving in the same direction towards the slice.

State and explain the effect, if any, of this change on the polarity of the Hall voltage.

[2]

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3a
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State and describe the conditions that must be satisfied for a copper wire, placed in a magnetic field, to experience a magnetic force.

 

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3b
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Two long parallel current-carrying wires are placed near to each other in a vacuum. 

Explain why these wires exert a magnetic force on each other. You may draw a labelled diagram if you wish.

 

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3c
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A long air-cored is connected to a power supply so that the solenoid creates a magnetic field. Fig. 1.1 shows a cross-section through the middle of the solenoid. 

 
20-1-3c-m-solenoid-magnetic-field-direction-sq-cie-a-level
Fig. 1.1
 
The direction of the magnetic field at point A is indicated by the arrow. The other points are labelled B, C and D. 
 
On Fig. 1.1, draw arrows to indicate the direction of the magnetic field at each of the points B, C and D. 

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3d
Sme Calculator2 marks

Compare the magnitude of the flux density of the magnetic field: 

(i)
At A and C
[1] 
(ii)
At A and D.
[1]

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