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Magnetism and Electromagnetic Induction MCQs — Physics (page 2)

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.

26. Magnetic flux is a:

  1. scalar quantity
  2. unit of force
  3. vector quantity
  4. dimensionless number

Answer: A) scalar quantity

Explanation: Product of two vectors (dot product). SLO P-09-E-38 · Knowledge

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27. The field around a straight wire gets weaker:

  1. only at the ends
  2. closer to the wire
  3. further from the wire
  4. nowhere — it is uniform

Answer: C) further from the wire

Explanation: B propto 1/r. SLO P-09-E-35 · Application

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28. A flux of 3 10^-4 Wb passes perpendicularly through 0.0015 m^2. The flux density is:

  1. 2 T
  2. 0.2 T
  3. 4.5 10^-7 T
  4. 0.02 T

Answer: B) 0.2 T

Explanation: B = PhiA = 0.2 T. SLO P-09-E-39 · Application

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29. Steel is not used for the core of an electromagnet that must be switched off because steel:

  1. cannot be magnetised
  2. keeps its magnetism (becomes a permanent magnet)
  3. is too light
  4. is non-metallic

Answer: B) keeps its magnetism (becomes a permanent magnet)

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

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30. A proton (charge 1.6 10^-19 C) moves at 3 10^5 m/s at 30^circ to a field of 0.2 T. The magnetic force on it is:

  1. 4.8 10^-15 N
  2. 2.4 10^-15 N
  3. 4.8 10^-14 N
  4. 9.6 10^-15 N

Answer: A) 4.8 10^-15 N

Explanation: F = Bqvsintheta = 4.8 10^-15 N. SLO P-09-E-32 · Application

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31. The field outside a long solenoid resembles that of:

  1. a bar magnet
  2. a flat coil only
  3. a straight wire
  4. a point charge

Answer: A) a bar magnet

Explanation: One end acts as N, the other as S. SLO P-09-E-35 · Application

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32. The force on a conductor in a magnetic field arises because:

  1. the magnetic field of the current interacts with the external field
  2. the wire heats up
  3. gravity changes
  4. the wire becomes charged

Answer: A) the magnetic field of the current interacts with the external field

Explanation: Interaction of fields. SLO P-09-E-29 · Understanding

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33. A flux density of 2.5 T passes perpendicularly through an area of 4 10^-4 m^2. The magnetic flux is:

  1. 0.01 Wb
  2. 0.001 Wb
  3. 1 10^-4 Wb
  4. 0.002 Wb

Answer: B) 0.001 Wb

Explanation: Phi = BA = 2.5 4 10^-4 = 0.001 Wb. SLO P-09-E-39 · Application

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34. A coil of 200 turns has a flux linkage of 0.4 Wb-turns. The flux through each turn is:

  1. 500 Wb
  2. 2 10^-3 Wb
  3. 80 Wb
  4. 0.4 Wb

Answer: B) 2 10^-3 Wb

Explanation: Phi = 0.4/200. SLO P-09-E-40 · Understanding

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35. In a velocity selector, the electric and magnetic fields are:

  1. absent
  2. both parallel to the velocity
  3. parallel to each other
  4. perpendicular to each other and to the particle's velocity

Answer: D) perpendicular to each other and to the particle's velocity

Explanation: Crossed fields. SLO P-09-E-34 · Understanding

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36. Reversing the magnetic field direction (same current):

  1. has no effect
  2. doubles the force
  3. removes the force
  4. reverses the force

Answer: D) reverses the force

Explanation: Direction depends on field direction. SLO P-09-E-29 · Understanding

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37. The Earth's magnetic flux through a 1 m^2 horizontal sheet where the vertical component of B is 4 10^-5 T is:

  1. 1 Wb
  2. 0 Wb
  3. 4 10^-5 Wb
  4. 4 10^5 Wb

Answer: C) 4 10^-5 Wb

Explanation: Only the vertical component passes through. SLO P-09-E-38 · Knowledge

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38. A seismometer's coil and magnet act together like:

  1. a capacitor
  2. a motor
  3. a generator
  4. a battery

Answer: C) a generator

Explanation: Motion → electrical signal. SLO P-09-E-43 · Application

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39. The magnetic particles in a ferrofluid are made of:

  1. a soft (temporary) magnetic material such as magnetite
  2. a permanent magnet material
  3. copper
  4. plastic

Answer: A) a soft (temporary) magnetic material such as magnetite

Explanation: They magnetise only when a field is applied. SLO P-09-E-09 · Understanding

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40. When a magnet is brought near a ferrofluid, the fluid:

  1. forms spikes along the magnetic field lines
  2. boils
  3. is unaffected
  4. freezes

Answer: A) forms spikes along the magnetic field lines

Explanation: The fluid follows the field. SLO P-09-E-09 · Understanding

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41. Flux density can be described as:

  1. flux × area
  2. area per unit flux
  3. flux per unit area
  4. flux × time

Answer: C) flux per unit area

Explanation: B = Phi/A. SLO P-09-E-38 · Knowledge

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42. In a velocity selector, the electric field is produced by:

  1. a p.d. across parallel plates
  2. a heater
  3. a bar magnet
  4. a coil

Answer: A) a p.d. across parallel plates

Explanation: E = V/d. SLO P-09-E-34 · Understanding

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43. Pushing a magnet into a coil connected to a galvanometer produces a deflection because:

  1. the galvanometer is magnetised
  2. the magnet carries current
  3. the changing magnetic flux induces an e.m.f.
  4. the coil is heated

Answer: C) the changing magnetic flux induces an e.m.f.

Explanation: Electromagnetic induction. SLO P-09-E-41 · Understanding

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44. A 20-turn coil of area 0.05 m^2 is perpendicular to a 0.8 T field, which falls to zero in 0.1 s. The average e.m.f. is:

  1. 16 V
  2. 8 V
  3. 0.4 V
  4. 4 V

Answer: B) 8 V

Explanation: mathcalE = NBAt = 8 V. SLO P-09-E-42 · Application

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45. Two wires 1 m apart each carrying 1 A experience a force per metre of:

  1. 4pi 10^-7 N
  2. 1 N
  3. 10^-7 N
  4. 2 10^-7 N

Answer: D) 2 10^-7 N

Explanation: 4pi 10^-72pi = 2 10^-7. SLO P-09-E-37 · Understanding

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46. In a velocity selector, E = 5000 V/m and B = 0.02 T are at right angles. The speed of particles that pass through undeflected is:

  1. 1.25 10^5 m/s
  2. 5 10^5 m/s
  3. 100 m/s
  4. 2.5 10^5 m/s

Answer: D) 2.5 10^5 m/s

Explanation: qE = Bqv Rightarrow v = EB = 2.5 10^5 m/s. SLO P-09-E-34 · Understanding

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47. The Earth's magnetic flux density is about:

  1. 5 T
  2. 5 10^-5 T
  3. 5 10^5 T
  4. 0.5 T

Answer: B) 5 10^-5 T

Explanation: About 50 μT. SLO P-09-E-31 · Knowledge

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48. A seismometer detects earthquakes using:

  1. electromagnetic induction between a magnet and a coil
  2. radioactivity
  3. the photoelectric effect
  4. static electricity

Answer: A) electromagnetic induction between a magnet and a coil

Explanation: Relative motion induces e.m.f. SLO P-09-E-43 · Application

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49. A compass needle placed near a current-carrying wire:

  1. spins forever
  2. is deflected
  3. is unaffected
  4. becomes demagnetised

Answer: B) is deflected

Explanation: Oersted's discovery. SLO P-09-E-28 · Knowledge

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50. 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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