MCQs / Physics / Magnetism and Electromagnetic Induction

Magnetism and Electromagnetic Induction MCQs — Physics (page 3)

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.

51. The minus sign in mathcalE = - Delta(NPhi)Delta t represents:

  1. Faraday's law
  2. Coulomb's law
  3. Lenz's law
  4. Ohm's law

Answer: C) Lenz's law

Explanation: Opposition. SLO P-09-E-41 · Understanding

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52. The particles in a ferrofluid are coated with a surfactant to:

  1. make them magnetic
  2. change their colour
  3. stop them clumping together
  4. make them heavier

Answer: C) stop them clumping together

Explanation: Keeps them suspended. SLO P-09-E-09 · Understanding

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53. Doubling the flux density doubles the force on a current-carrying wire because:

  1. F propto 1B
  2. F = BILsintheta propto B
  3. the current doubles
  4. F propto B^2

Answer: B) F = BILsintheta propto B

Explanation: Direct proportion. SLO P-09-E-31 · Knowledge

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54. A ferrofluid in a strong magnetic field becomes:

  1. magnetised and is attracted to regions of strong field
  2. repelled from the magnet
  3. electrically charged
  4. transparent

Answer: A) magnetised and is attracted to regions of strong field

Explanation: Pulled towards the magnet. SLO P-09-E-09 · Understanding

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55. For a charge in a magnetic field, the centripetal force is provided by:

  1. the magnetic force Bqv
  2. air resistance
  3. gravity
  4. the electric force

Answer: A) the magnetic force Bqv

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

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56. If the speed of the particle is doubled, the radius of its circular path:

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

Answer: C) doubles

Explanation: r propto v. SLO P-09-E-33 · Understanding

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57. A strong laboratory magnet produces a flux density of about:

  1. 1000 T
  2. 0.1–1 T
  3. 10^-9 T
  4. 10^-5 T

Answer: B) 0.1–1 T

Explanation: MRI scanners: 1.5–3 T. SLO P-09-E-31 · Knowledge

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58. The speed of a charged particle moving in a circle in a magnetic field:

  1. oscillates
  2. decreases
  3. stays constant
  4. increases

Answer: C) stays constant

Explanation: Magnetic force does no work. SLO P-09-E-33 · Understanding

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59. The definition of magnetic flux uses the area:

  1. of the wire's cross-section
  2. of the magnet's pole
  3. perpendicular to the direction of the field
  4. parallel to the field

Answer: C) perpendicular to the direction of the field

Explanation: As in the SLO. SLO P-09-E-38 · Knowledge

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60. When the N pole of a magnet is withdrawn from a coil, the near end of the coil becomes:

  1. negatively charged
  2. neutral
  3. a north pole
  4. a south pole (attracting the magnet)

Answer: D) a south pole (attracting the magnet)

Explanation: Opposes the withdrawal. SLO P-09-E-41 · Understanding

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61. A neutral particle entering a velocity selector:

  1. is stopped
  2. is deflected by B
  3. is deflected by E
  4. passes straight through whatever its speed

Answer: D) passes straight through whatever its speed

Explanation: No forces on it. SLO P-09-E-34 · Understanding

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62. The Earth's magnetic field is roughly like that of:

  1. a single pole
  2. a bar magnet
  3. a flat coil only
  4. a straight wire

Answer: B) a bar magnet

Explanation: Geomagnetic field. SLO P-09-E-28 · Knowledge

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63. A straight conductor 1.5 m long moves at 20 m/s at right angles to a 0.05 T field. The induced e.m.f. is:

  1. 0.00375 V
  2. 0.75 V
  3. 3 V
  4. 1.5 V

Answer: D) 1.5 V

Explanation: mathcalE = BLv = 1.5 V. SLO P-09-E-42 · Application

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64. The flux through each of 200 turns of a coil changes by 0.03 Wb in 0.1 s. The average induced e.m.f. is:

  1. 60 V
  2. 0.3 V
  3. 30 V
  4. 120 V

Answer: A) 60 V

Explanation: mathcalE = N DeltaPhiDelta t = 200 0.030.1 = 60 V. SLO P-09-E-42 · Application

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65. Holding the magnet still inside the coil gives:

  1. a steady deflection
  2. a growing deflection
  3. a reversed deflection
  4. no deflection

Answer: D) no deflection

Explanation: No change of flux. SLO P-09-E-41 · Understanding

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66. To find the force direction on wire 2 due to wire 1, you use:

  1. Lenz's law only
  2. Coulomb's law
  3. Newton's law of gravitation
  4. the right-hand grip rule for the field of wire 1 and then Fleming's left-hand rule for wire 2

Answer: D) the right-hand grip rule for the field of wire 1 and then Fleming's left-hand rule for wire 2

Explanation: Two-step method. SLO P-09-E-37 · Understanding

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67. One tesla is the flux density that produces a force of:

  1. 1 J on 1 C
  2. 1 N on a charge of 1 C at rest
  3. 1 W per m^2
  4. 1 N on a 1 m wire carrying 1 A at right angles to the field

Answer: D) 1 N on a 1 m wire carrying 1 A at right angles to the field

Explanation: Definition. SLO P-09-E-31 · Knowledge

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68. The two wires of a mains flex carry currents in opposite directions, so they:

  1. twist together
  2. repel slightly
  3. attract strongly
  4. exert no force

Answer: B) repel slightly

Explanation: Opposite currents. SLO P-09-E-37 · Understanding

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69. Ferrofluids were first developed by NASA for:

  1. space suits
  2. rocket engines' fire
  3. controlling fuel flow in zero gravity
  4. radio communications

Answer: C) controlling fuel flow in zero gravity

Explanation: Moving fuel with magnets. SLO P-09-E-09 · Understanding

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70. A straight conductor 0.2 m long moves at 4 m/s at right angles to a 0.5 T field. The induced e.m.f. is:

  1. 0.2 V
  2. 0.025 V
  3. 0.4 V
  4. 0.8 V

Answer: C) 0.4 V

Explanation: mathcalE = BLv = 0.4 V. SLO P-09-E-42 · Application

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71. A circular loop of radius 5 cm is perpendicular to a 0.2 T field. The flux through it is:

  1. 0.00157 Wb
  2. 7.85 10^-4 Wb
  3. 0.00314 Wb
  4. 5 10^-4 Wb

Answer: A) 0.00157 Wb

Explanation: A = pi r^2 = 0.00785 m^2; Phi = BA = 0.00157 Wb. SLO P-09-E-39 · Application

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72. When the N pole of a magnet is pushed into a coil, the near end of the coil becomes:

  1. neutral
  2. a south pole (attracting the magnet)
  3. positively charged
  4. a north pole (repelling the magnet)

Answer: D) a north pole (repelling the magnet)

Explanation: Opposes the approach. SLO P-09-E-41 · Understanding

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73. A coil of area 0.1 m^2 is in a 0.8 T field; the field makes 30^circ with the normal to the coil. The flux through the coil is:

  1. 0.0346 Wb
  2. 0.693 Wb
  3. 0.139 Wb
  4. 0.0693 Wb

Answer: D) 0.0693 Wb

Explanation: Phi = BAcostheta = 0.8 0.1 cos 30^circ = 0.0693 Wb. SLO P-09-E-39 · Application

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74. In a velocity selector, E = 3 10^5 V/m and B = 0.6 T are at right angles. The speed of particles that pass through undeflected is:

  1. 2.5 10^5 m/s
  2. 5 10^5 m/s
  3. 1.8 10^5 m/s
  4. 1 10^6 m/s

Answer: B) 5 10^5 m/s

Explanation: qE = Bqv Rightarrow v = EB = 5 10^5 m/s. SLO P-09-E-34 · Understanding

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75. 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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