DP IB Physics: SL

Topic Questions

IBPhysics: SLDPTopic Questions5. Electricity & Magnetism5.4 Magnetic Effects of Electric Currents

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First teaching 2014

Last exams 2024

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5.4 Magnetic Effects of Electric Currents

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1
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Which of the following statements about magnetic fields is incorrect?

  • The strength of a magnetic field is also known as the magnetic flux density.

  • There is a force on a conductor carrying a current at 90° to magnetic field lines.

  • The magnetic flux density is measured in units of Tesla, T.

  • A conductor carrying a current parallel to magnetic field lines experiences a magnetic force.

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2
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A current of 2.0 A flows in a wire of length 1.5 m. It is placed in a magnetic field of flux density 5 T such that the angle between the current and the field is 90°.

What is the magnitude of the magnetic force on the wire?

  • 0 N

  • 0.15 N

  • 15 N

  • 150 N

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3
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Fleming’s Left-Hand Rule is a useful method to determine the direction of the force exerted on a current-carrying conductor in a magnetic field.

When used correctly, the direction of the thumb indicates the corresponding direction of which quantity?

  • Conventional current.

  • Electron flow.

  • Force.

  • Magnetic field.

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4
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A proton with mass, m = 1.6 × 10−19 kg moves parallel to a magnetic field of flux density       B = 0.5 T with a speed, v = 200 m s–1.

What is the magnitude of force exerted on the particle?

  • 0 N

  • 1.6 × 10–14 N

  • 1.6 × 10–11 N

  • 10 N

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5
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A horizontal straight wire of mass m and length L is placed in a magnetic field with magnetic field of flux density B. The wire and field are perpendicular, so that θ = 90° and sinθ = 1.

qu-6

What size of current does the wire need to carry in order for it to ‘float’ above the surface when in the magnetic field?

  • I space equals space 0

  • I space equals space m g

  • I space equals space B L sin theta

  • I space equals space fraction numerator m g over denominator B L end fraction

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6
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A beam of electrons enters a uniform magnetic field which causes it to change direction, as shown.

5-4-mcq-6-qun-sl-easy-mcq-phy-

What is the direction of the magnetic field?

  • Out of the page and perpendicular to it.

  • Into the page and perpendicular to it.

  • In the direction marked Up.

  • In the direction marked Down.

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7
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A current is passed through a wire running vertically upwards through a hole in a flat sheet of card, as shown.

5-4-mcq-7-sl-easy-mcq-phy

Which line correctly describes the induced magnetic field in terms of its direction and orientation relative to the card?

  Direction Orientation to card
A. anti-clockwise same plane
B. anti-clockwise perpendicular
C. clockwise same plane
D. clockwise perpendicular

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8
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A current moves through a solenoid as shown. 

5-4-mcq-8-qun-sl-easy-mcq-phy

Which diagram has the North and South poles of the solenoid, and the magnetic field lines, all correctly marked?

  • 5-4-mcq-8-answer-a-right-sl-easy-mcq-phy

  • 5-4-mcq-8-answer-b-wrong-sl-easy-mcq-phy

  • 5-4-mcq-8-answer-c-wrong-sl-easy-mcq-phy

  • 5-4-mcq-8-answer-d-wrong-sl-easy-mcq-phy

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9
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Two current-carrying wires are placed in parallel with each other. Which statements correctly describe the situation?

  1. When the conductors attract, the direction of the magnetic forces will be towards each other
  2. When the conductors repel, the direction of the magnetic forces will be away from each other
  3. The magnitude of each force depends on the amount of current and the length of the wire

  • I only

  • I and II only

  • II and III only

  • I, II and III

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10
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A current-carrying wire is positioned between two magnets as shown. Which arrow shows the direction of the force on the wire?

mcq-10-qun-1-sl-easy-mcq-phy

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1
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Three long parallel straight wires, X, Y and Z, are equally separated and placed in the same plane in a vacuum. They carry a current of I, 2I and 4I respectively, as shown: 

5-4-sl-mcq-hard-q1-phy

It is known that the magnetic flux density B at a distance r due to a long straight wire carrying current I is given by: 

B equals fraction numerator mu subscript 0 I over denominator 2 pi r end fraction  

where μ0 is the permeability of free space.

What is the force per unit length acting on wire X? 

  • 0

  • fraction numerator mu subscript 0 I squared over denominator pi r end fraction N m–1

  • fraction numerator mu subscript 0 I squared over denominator 2 pi r end fraction N m–1

  • fraction numerator mu subscript 0 I squared over denominator 3 pi r end fraction N m–1

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2
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A plotting compass is placed next to a vertical wire AB. When there is no current in the wire, the compass is deflected North as shown in the image below: 

5-4-sl-mcq-hard-q2-phy

Which diagram shows a possible direction for the compass when a current flows in the direction A to B? 

5-4-sl-mcq-hard-q2_2-phy

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3
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The magnetic field produced by a straight current carrying wire is in

  • a single plane parallel to the current. 

  • all planes parallel to the current.

  • a single plane perpendicular to the current. 

  • all planes perpendicular to the current. 

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4
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A liquid that contains a suspension of positive and negative ions flows through a square pipe as shown. 

5-4-sl-mcq-hard-q4-phy

An electric field is set up in the pipe

  • vertically downwards

  • vertically upwards

  • horizontally rightwards

  • horizontally leftwards

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5
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A direct current I is made to pass through a swing that is mounted to the ceiling, such that it can swing freely. A permanent magnet is fixed directly below, with its south pole S facing the swing. 

5-4-sl-mcq-hard-q5-phy

The swing will

  • deflect in the direction of P and stay there. 

  • oscillate back and forth along P. 

  • deflect in the direction of Q and stay there. 

  • oscillate back and forth along Q. 

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6
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A straight wire PQ carrying a constant current I is placed normally to a uniform magnetic field of flux density B as represented by the dotted line. 

5-4-sl-mcq-hard-q6-phy

The current-carrying wire is then rotated clockwise through an angle θ about an axis perpendicular to the plane of the image. 

Which of the following graphs shows how the magnitude of the magnetic force F on the wire varies for 0 less or equal than theta less or equal than pi over 2 radians?

5-4-sl-mcq-hard-q6_2-phy

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7
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Two long parallel wires carry equal currents in opposite directions. What exists at the point in space that is exactly midway between the wires and in the plane of the wires? 

  • A magnetic field parallel to the wires

  • A magnetic field at right angles to the plane of the wires

  • An electric field parallel to the wires

  • An electric field at right angles to the plane of the wires

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8
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A loosely-coiled light spring is suspended from a fixed point. 

5-4-sl-mcq-hard-q8-phy

When the switch is closed, 

  • the spring oscillates vertically. 

  • the spring compresses. 

  • the string stretches. 

  • nothing happens to the spring. 

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9
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A doubly charged ion moves in a uniform magnetic field of flux density B in a circle of orbital radius r at speed v. What is the flux density which would maintain an ion of charge 4e of the same mass in a circle of the same orbital radius at the same speed? 

  • B over 2

  • fraction numerator 3 B over denominator 4 end fraction

  • 2 B

  • 4 B

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10
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An electron moves along the axis of a solenoid carrying a current. 

Which of the following statements is correct about the magnetic force on the electron? 

  • No force acts. 

  • The forces acts normally to the electron's velocity. 

  • The force acts radially outwards. 

  • The force acts radially inwards. 

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11
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A particle P with charge q and mass m is fired with kinetic energy K into a region between two metal plates.


qu12-

If the magnetic flux density between the plates is B, what is the minimum magnitude of B which ensures the particle does not collide with the opposite plate?

  • square root of fraction numerator m K over denominator q d end fraction end root

  • fraction numerator m K over denominator q d end fraction

  • fraction numerator square root of 2 m K end root over denominator q d end fraction

  • fraction numerator 2 m K over denominator q d end fraction

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1
Sme Calculator1 mark

Which of the following statements about magnetic fields is incorrect?

  • The strength of a magnetic field is also known as the magnetic flux density

  • There is a force on a conductor carrying a current at 90º to magnetic field lines

  • The magnetic flux density is measured in units of Tesla, T 

  • There is a force on a current carrying conductor parallel to magnetic field lines

Choose your answer

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2
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A current of 3.0 mA flows in a wire of length 2.0 m. It is placed in a magnetic field of flux density 4 T such that the angle between the current and the field is 90­º.

What is the magnitude of the magnetic force on the wire?

  • 0.012 N   

  • 0.024 N

  • 8 N

  • 24 N

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3
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A proton, p, moves normally across a magnetic field of flux density B T with a speed of v m s–1.

What is the magnitude of force exerted on the particle?

  • Bpv

  • BIL

  • (1.6 × 10–19) Bv

  • (1.6 × 10–19) Bv sin θ

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4
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A negatively charged particle is at rest in a magnetic field B. The force on the particle is:

  • At right angles to B

  • Opposite to B

  • Parallel to B

  • Zero

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5
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An electron enters a region of a magnetic field.

In which case is the initial force on the electron directed towards the bottom of the page?

q15_magnetic-effects-of-electric-currents_ib-sl-physics-mcq

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6
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Two long parallel wires carry equal currents in opposite directions. What field do the two wires produce at point Y, which is midway between the wires and on the plane of the paper?

q16_magnetic-effects-of-electric-currents_ib-sl-physics-mcq

  • A magnetic field at right angles to the plane of the page

  • An electric field at right angles to the plane of the page

  • An electric field parallel to the wires

  • A magnetic field parallel to the wires

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7
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A beam of electrons enters a region in which there are uniform magnetic and electric fields directed at right angles to each other. The field strengths are adjusted such that the beam remains undeflected, as shown in the diagram below.

q17_magnetic-effects-of-electric-currents_ib-sl-physics-mcq

Which of the following statements is incorrect?

  • Conventional current flows from right to left in this diagram 

  • The velocity of the electron beam v is equal to the ratio of the magnetic flux density B to the electric field strength E

  • The magnetic force on the electron beam is in the direction indicated ‘south’

  • The electric force on the electron beam is in the direction indicated ‘north’

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8
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A plotting compass is placed next to a vertical wire AB. When there is no current in the wire, the compass points North due to an external magnetic field.

q18_magnetic-effects-of-electric-currents_ib-sl-physics-mcq

Which diagram shows a possible direction for the compass to point when a current passes from A to B?

q18_2_magnetic-effects-of-electric-currents_ib-sl-physics-mcq

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91 mark

An alpha particle travelling at speed v perpendicular to a magnetic field of strength B experiences a force F.

What is the force acting on an electron travelling at v over 2 perpendicular to a magnetic field of strength B over 2?

  • 0

  • fraction numerator negative F over denominator 6 end fraction

  • F over 4

  • fraction numerator negative F over denominator 8 end fraction

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10
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A proton p is at downwards from top to bottom between the poles of two horizontal magnets.

q20_magnetic-effects-of-electric-currents_ib-sl-physics-mcq

The magnetic force on the proton is:

  • From top to bottom

  • From left to right

  • zero

  • Out of the page

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