MCQs / Physics / Magnetism and Electromagnetic Induction

Magnetism and Electromagnetic Induction MCQs — Physics (page 4)

255 multiple-choice questions on Magnetism and Electromagnetic Induction from Physics, each with the correct answer and, where available, a teacher's explanation. Read through them to revise the chapter, then practise the same questions one by one to test yourself.

76. In hard-disk drives, ferrofluids are used as:

  1. the power supply
  2. the display
  3. data storage
  4. seals that keep dust out around rotating shafts

Answer: D) seals that keep dust out around rotating shafts

Explanation: Liquid seals held by magnets. SLO P-09-E-09 · Understanding

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77. A neutral point in a magnetic field is where:

  1. the poles meet
  2. the resultant field is zero
  3. the field is strongest
  4. field lines cross

Answer: B) the resultant field is zero

Explanation: Fields cancel. SLO P-09-E-28 · Knowledge

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78. A current flows vertically upward in a wire. Looking down from above, the field lines circle:

  1. outward
  2. inward
  3. clockwise
  4. anticlockwise

Answer: D) anticlockwise

Explanation: Right-hand grip rule. SLO P-09-E-35 · Application

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79. A loop of wire carrying current in a magnetic field experiences:

  1. only a sideways push
  2. a pull towards the north pole only
  3. a turning effect (torque)
  4. no effect

Answer: C) a turning effect (torque)

Explanation: Principle of the motor. SLO P-09-E-29 · Understanding

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80. F = BIL and F = Bqv are linked because a current I in length L is equivalent to:

  1. IL = qv for the charge carriers
  2. I = qv
  3. L = qv
  4. IL = q/v

Answer: A) IL = qv for the charge carriers

Explanation: I = q/t and v = L/t. SLO P-09-E-32 · Application

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81. A smaller unit sometimes used for weak fields is the gauss, where 1 T equals:

  1. 10^3 gauss
  2. 10^4 gauss
  3. 10^-4 gauss
  4. 1 gauss

Answer: B) 10^4 gauss

Explanation: Earth ≈ 0.5 gauss. SLO P-09-E-31 · Knowledge

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82. The spring in a seismometer is important because:

  1. it lets the heavy suspended mass stay nearly still while the frame moves
  2. it produces electricity
  3. it measures temperature
  4. it heats the coil

Answer: A) it lets the heavy suspended mass stay nearly still while the frame moves

Explanation: Inertial reference. SLO P-09-E-43 · Application

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83. A charged particle moving perpendicular to a uniform magnetic field moves in:

  1. a circle
  2. a straight line
  3. a zig-zag
  4. a parabola

Answer: A) a circle

Explanation: Force always perpendicular to velocity. SLO P-09-E-33 · Understanding

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84. If both E and B in a velocity selector are doubled, the selected speed:

  1. quadruples
  2. doubles
  3. stays the same
  4. halves

Answer: C) stays the same

Explanation: v = E/B. SLO P-09-E-34 · Understanding

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85. The radius of the path of a charged particle in a magnetic field is:

  1. r = mvBq
  2. r = Bqmv
  3. r = mv^2Bq
  4. r = Bqmv

Answer: A) r = mvBq

Explanation: From Bqv = mv^2/r. SLO P-09-E-33 · Understanding

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86. If the distance between two parallel wires is doubled, the force between them becomes:

  1. unchanged
  2. double
  3. one quarter
  4. half

Answer: D) half

Explanation: F propto 1/d. SLO P-09-E-37 · Understanding

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87. Increasing the number of turns on a seismometer coil:

  1. reduces the sensitivity
  2. stops it working
  3. increases the sensitivity (larger e.m.f.)
  4. has no effect

Answer: C) increases the sensitivity (larger e.m.f.)

Explanation: mathcalE propto N. SLO P-09-E-43 · Application

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88. An electromagnet is used in:

  1. thermometers
  2. solar panels
  3. scrapyard cranes and electric bells
  4. light bulbs

Answer: C) scrapyard cranes and electric bells

Explanation: Switchable magnetism. SLO P-09-E-36 · Knowledge

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89. Flux linkage is used because:

  1. it is a vector
  2. the induced e.m.f. in a coil depends on the change in flux through all its turns
  3. it is easier to measure than current
  4. coils have only one turn

Answer: B) the induced e.m.f. in a coil depends on the change in flux through all its turns

Explanation: Faraday's law uses NPhi. SLO P-09-E-40 · Understanding

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90. When the magnet is removed, a ferrofluid:

  1. stays spiky permanently
  2. evaporates
  3. returns to an ordinary liquid shape
  4. becomes a solid magnet

Answer: C) returns to an ordinary liquid shape

Explanation: Soft magnetic material: magnetism is temporary. SLO P-09-E-09 · Understanding

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91. Magnetic field lines:

  1. always cross
  2. never cross each other
  3. cross at the poles
  4. end in mid-air

Answer: B) never cross each other

Explanation: Unique direction at each point. SLO P-09-E-28 · Knowledge

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92. The magnetic field at the centre of a flat coil can be increased by:

  1. reversing the current
  2. increasing the radius
  3. using copper of lower resistance only
  4. increasing the current or the number of turns

Answer: D) increasing the current or the number of turns

Explanation: B = mu0NI2r. SLO P-09-E-35 · Application

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93. A soft magnetic material is one that:

  1. is a liquid
  2. cannot be magnetised
  3. stays magnetised permanently
  4. is easily magnetised and demagnetised

Answer: D) is easily magnetised and demagnetised

Explanation: Like soft iron. SLO P-09-E-09 · Understanding

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94. Doubling the speed of a charge moving perpendicular to a field makes the magnetic force:

  1. half
  2. double
  3. four times
  4. unchanged

Answer: B) double

Explanation: F propto v. SLO P-09-E-32 · Application

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95. If a coil's circuit is open (not complete), moving a magnet into it produces:

  1. a current but no e.m.f.
  2. a permanent magnet
  3. an induced e.m.f. but no current
  4. neither

Answer: C) an induced e.m.f. but no current

Explanation: E.m.f. needs no circuit; current does. SLO P-09-E-41 · Understanding

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96. Transformer cores are made of soft iron to:

  1. increase resistance
  2. insulate the coils
  3. reduce weight
  4. concentrate the magnetic flux and link the coils

Answer: D) concentrate the magnetic flux and link the coils

Explanation: Strong flux linkage. SLO P-09-E-36 · Knowledge

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97. A larger induced e.m.f. in a seismometer indicates:

  1. no earthquake
  2. a power failure
  3. stronger ground movement
  4. weaker ground movement

Answer: C) stronger ground movement

Explanation: Larger vibrations. SLO P-09-E-43 · Application

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98. Soft iron is used in electromagnets because it:

  1. magnetises strongly and loses its magnetism when the current stops
  2. stays magnetised permanently
  3. doesn't magnetise
  4. is a good insulator

Answer: A) magnetises strongly and loses its magnetism when the current stops

Explanation: Soft magnetic material. SLO P-09-E-36 · Knowledge

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99. A wire carrying current due north lies in a field pointing due east. The force on the wire is:

  1. vertically upward
  2. due south
  3. due west
  4. vertically downward

Answer: D) vertically downward

Explanation: Left hand: field east, current north ⇒ thrust down. SLO P-09-E-30 · Application

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100. 1 T = 1 Wb m^-2 shows that flux density is:

  1. area per unit flux
  2. flux per unit area
  3. flux times area
  4. force per charge

Answer: B) flux per unit area

Explanation: B = Phi/A. SLO P-09-E-31 · Knowledge

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