MCQs / Physics / Magnetism and Electromagnetic Induction

Magnetism and Electromagnetic Induction MCQs — Physics (page 6)

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.

126. Iron filings around a vertical current-carrying wire through horizontal card form:

  1. straight lines
  2. circles around the wire
  3. radial spokes
  4. random patterns

Answer: B) circles around the wire

Explanation: Classic demonstration. SLO P-09-E-35 · Application

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127. An aircraft with wingspan 40 m flies horizontally at 250 m/s where the vertical field is 5 10^-5 T. The e.m.f. between its wingtips is:

  1. 500 V
  2. 5 V
  3. 0.5 V
  4. 0.05 V

Answer: C) 0.5 V

Explanation: mathcalE = BLv = 5 10^-5 40 250. SLO P-09-E-42 · Application

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128. A square coil of side 10 cm is perpendicular to a 0.3 T field. The flux is:

  1. 0.03 Wb
  2. 3 10^-2 Wb
  3. 3 Wb
  4. 3 10^-3 Wb

Answer: D) 3 10^-3 Wb

Explanation: A = 0.01 m^2. SLO P-09-E-39 · Application

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129. A coil of 250 turns and area 0.002 m^2 is perpendicular to a 1.2 T field. The flux linkage is:

  1. 0.0024 Wb-turns
  2. 0.6 Wb-turns
  3. 0.3 Wb-turns
  4. 1.2 Wb-turns

Answer: B) 0.6 Wb-turns

Explanation: NPhi = NBA = 250 1.2 0.002 = 0.6 Wb-turns. SLO P-09-E-40 · Understanding

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130. Without a core, the field inside a solenoid depends on:

  1. the colour of the wire
  2. the current and the number of turns per unit length
  3. the room temperature only
  4. the battery's mass

Answer: B) the current and the number of turns per unit length

Explanation: B = mu0nI. SLO P-09-E-36 · Knowledge

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131. Two parallel wires carrying currents in opposite directions:

  1. repel each other
  2. attract each other
  3. exert no force
  4. twist

Answer: A) repel each other

Explanation: Fields between them add. SLO P-09-E-37 · Understanding

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132. A 0.5 m wire carrying 4 A perpendicular to a field feels 1 N. B is:

  1. 0.5 T
  2. 8 T
  3. 0.125 T
  4. 2 T

Answer: A) 0.5 T

Explanation: B = 14 0.5. SLO P-09-E-31 · Knowledge

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133. The flux linkage of a 300-turn coil changes from 0.6 Wb-turns to 0 in 0.2 s. The average induced e.m.f. is:

  1. 3 V
  2. 0.6 V
  3. 900 V
  4. 0.12 V

Answer: A) 3 V

Explanation: mathcalE = Delta(NPhi)Delta t = 0.60.2. SLO P-09-E-40 · Understanding

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134. The electrical signal from a seismometer is alternating because:

  1. the coil is AC powered
  2. the battery alternates
  3. the magnet rotates continuously
  4. the ground vibrates back and forth, reversing the relative motion

Answer: D) the ground vibrates back and forth, reversing the relative motion

Explanation: Direction of induced e.m.f. reverses. SLO P-09-E-43 · Application

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135. Magnetic fields are produced by:

  1. moving charges (currents) and magnetic materials
  2. stationary charges only
  3. sound waves
  4. masses

Answer: A) moving charges (currents) and magnetic materials

Explanation: Electric currents create magnetism. SLO P-09-E-28 · Knowledge

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136. Magnetic flux density is a:

  1. unit of energy
  2. dimensionless ratio
  3. vector quantity
  4. scalar quantity

Answer: C) vector quantity

Explanation: It has direction. SLO P-09-E-31 · Knowledge

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137. Doctors are researching ferrofluids to:

  1. make X-rays
  2. guide drugs to specific parts of the body using magnets
  3. measure blood pressure
  4. replace blood

Answer: B) guide drugs to specific parts of the body using magnets

Explanation: Targeted drug delivery. SLO P-09-E-09 · Understanding

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138. Ferrofluids are used in loudspeakers to:

  1. amplify the signal
  2. store electricity
  3. produce the sound directly
  4. cool the voice coil and damp its vibrations

Answer: D) cool the voice coil and damp its vibrations

Explanation: Held in the gap by the magnet. SLO P-09-E-09 · Understanding

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139. A straight conductor 0.1 m long moves at 0.5 m/s at right angles to a 1.2 T field. The induced e.m.f. is:

  1. 0.03 V
  2. 0.06 V
  3. 0.12 V
  4. 0.24 V

Answer: B) 0.06 V

Explanation: mathcalE = BLv = 0.06 V. SLO P-09-E-42 · Application

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140. The magnetic field lines around a long straight current-carrying wire are:

  1. radial lines
  2. spirals
  3. straight lines parallel to the wire
  4. concentric circles centred on the wire

Answer: D) concentric circles centred on the wire

Explanation: In planes perpendicular to the wire. SLO P-09-E-35 · Application

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141. A coil of 500 turns and area 0.004 m^2 is perpendicular to a 0.05 T field. The flux linkage is:

  1. 2 10^-4 Wb-turns
  2. 0.1 Wb-turns
  3. 0.05 Wb-turns
  4. 0.2 Wb-turns

Answer: B) 0.1 Wb-turns

Explanation: NPhi = NBA = 500 0.05 0.004 = 0.1 Wb-turns. SLO P-09-E-40 · Understanding

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142. Reversing the current in a solenoid:

  1. reverses its north and south poles
  2. removes its field
  3. has no effect
  4. doubles its field

Answer: A) reverses its north and south poles

Explanation: Field direction depends on current. SLO P-09-E-35 · Application

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143. A uniform magnetic field is shown by:

  1. crossing lines
  2. radial lines
  3. parallel, equally spaced lines
  4. concentric circles

Answer: C) parallel, equally spaced lines

Explanation: e.g. between flat poles. SLO P-09-E-28 · Knowledge

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144. A 100-turn coil of area 0.01 m^2 is perpendicular to a 0.4 T field, which falls to zero in 0.2 s. The average e.m.f. is:

  1. 1 V
  2. 4 V
  3. 2 V
  4. 0.02 V

Answer: C) 2 V

Explanation: mathcalE = NBAt = 2 V. SLO P-09-E-42 · Application

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145. A proton and an electron with the same speed enter the same field perpendicularly. Compared with the electron, the proton's circle is:

  1. the same size
  2. much larger, and curves the other way
  3. much smaller, same direction
  4. a straight line

Answer: B) much larger, and curves the other way

Explanation: Larger mass; opposite charge. SLO P-09-E-33 · Understanding

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146. An electron (charge 1.6 10^-19 C) moves at 5 10^6 m/s at 60^circ to a field of 0.01 T. The magnetic force on it is:

  1. 1.39 10^-14 N
  2. 6.93 10^-15 N
  3. 3.46 10^-15 N
  4. 6.93 10^-14 N

Answer: B) 6.93 10^-15 N

Explanation: F = Bqvsintheta = 6.93 10^-15 N. SLO P-09-E-32 · Application

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147. Wire A carries 2 A; wire B, parallel, carries 6 A. The force on A compared with that on B is:

  1. three times smaller
  2. three times larger
  3. equal in size
  4. zero

Answer: C) equal in size

Explanation: Newton's third law. SLO P-09-E-37 · Understanding

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148. The force per unit length between two long parallel wires is:

  1. FL = mu0I1I2d
  2. FL = mu0I1I22pi d^2
  3. FL = I1I2d
  4. FL = mu0I1I22pi d

Answer: D) FL = mu0I1I22pi d

Explanation: Used to define the ampere historically. SLO P-09-E-37 · Understanding

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149. A 0.05 m wire carrying 2 A at right angles to a field experiences 0.02 N. The flux density is:

  1. 0.002 T
  2. 0.2 T
  3. 0.4 T
  4. 0.1 T

Answer: B) 0.2 T

Explanation: B = FIL = 0.2 T. SLO P-09-E-30 · Application

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150. The e.m.f. induced in a seismometer coil is proportional to:

  1. the temperature of the rock
  2. the size of the case
  3. the mass of the Earth
  4. the rate of relative motion (velocity) between the magnet and the coil

Answer: D) the rate of relative motion (velocity) between the magnet and the coil

Explanation: Faster motion, larger e.m.f. SLO P-09-E-43 · Application

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