19 exam-style questions on Physics · Electromagnetic induction, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Inductance, generators and transformers10 questions
Ten Physics · Electromagnetic induction questions with answers
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. An ideal transformer has 2200 turns on its primary coil, which is connected to a 220 V AC supply. To give an output of 11 V, the number of turns on the secondary coil must be
A
44000
B
110
C
22
D
1100
Show answer
Answer: B. Vs/Vp = Ns/Np, so Ns = 2200 × 11/220 = 110 turns. Turning the ratio upside down gives 44000.
2. An AC generator produces a peak EMF E0 at frequency f. If its coil is turned twice as fast, the peak EMF and the frequency become
A
2E0 and f
B
E0 and 2f
C
4E0 and 2f
D
2E0 and 2f
Show answer
Answer: D. The peak EMF E0 = NωAB is proportional to ω, and f = ω/2π, so turning the coil twice as fast doubles both. The peak EMF rises because the flux now changes twice as fast.
3. The current in a coil of self-inductance 0.30 H falls steadily from 5.0 A to 1.0 A in 0.20 s. The magnitude of the self-induced EMF is
A
7.5 V
B
6.0 V
C
9.0 V
D
0.24 V
Show answer
Answer: B. ε = L ΔI/Δt = 0.30 × (5.0 − 1.0) ÷ 0.20 = 6.0 V. Using the starting current of 5.0 A instead of the change gives 7.5 V.
4. A flat loop of area 0.20 m2 is in a uniform magnetic field of 0.50 T. The field makes an angle of 30° with the plane of the loop. The magnetic flux through the loop is
A
0.087 Wb
B
0.050 Wb
C
0.10 Wb
D
0.025 Wb
Show answer
Answer: B. Φ = BA cos θ, where θ is the angle between B and the normal to the loop: 90° − 30° = 60°. So Φ = 0.50 × 0.20 × cos 60° = 0.050 Wb. Taking θ as 30° gives 0.087 Wb.
5. The iron core of a transformer is made of thin insulated sheets (laminations) rather than one solid block in order to
A
increase the number of turns that can be wound
B
reduce the resistance of the copper windings
C
allow the transformer to work on direct current
D
reduce the energy lost through eddy currents
Show answer
Answer: D. The changing flux induces eddy currents in the core. The thin insulated layers break up their paths, so the eddy currents, and the heat they waste, are much smaller.
6. The henry, the SI unit of inductance, is equivalent to
A
V A s−1
B
Wb A
C
V s A−1
D
Ω s−1
Show answer
Answer: C. ε = L ΔI/Δt, so L = εΔt/ΔI and 1 H = 1 V s A−1 (which also equals Wb A−1 and Ω s).
7. The north pole of a bar magnet is pushed towards one face of a closed coil. While the magnet is moving, that face of the coil
A
acts as a south pole and attracts the magnet
B
acts as a north pole and repels the magnet
C
acts as a north pole only once the magnet has stopped
D
shows no pole, as the coil has no iron core
Show answer
Answer: B. The induced current opposes the approach of the magnet, so the near face becomes a north pole and repels it; the work done against this repulsion becomes electrical energy. Once the magnet stops, the flux no longer changes and there is no current.
8. The SI unit of magnetic flux is the
A
tesla
B
weber
C
henry
D
volt
Show answer
Answer: B. Φ = BA cos θ, so its unit is T m2, called the weber (Wb). The tesla (Wb m−2) is the unit of flux density, and the henry is the unit of inductance.
9. The mutual inductance of a pair of coils can be increased by
A
moving the coils further away from each other
B
turning one coil so that their axes are at right angles
C
winding both coils on a common soft-iron core
D
increasing the current in the primary coil
Show answer
Answer: C. Mutual inductance depends on the numbers of turns, the shape and position of the coils and the core; a common soft-iron core links nearly all the flux of one coil with the other. It does not depend on the current, and separating the coils or crossing their axes reduces the flux linkage.
10. The coil of an AC generator rotates at a steady rate in a uniform magnetic field. The induced EMF is greatest at the instant when the plane of the coil is
A
perpendicular to the magnetic field
B
at 45° to the magnetic field
C
at 30° to the magnetic field
D
parallel to the magnetic field
Show answer
Answer: D. When the plane of the coil lies along the field, the flux through it is zero but changing fastest, because the sides of the coil cut the field lines at right angles. When the plane is perpendicular to the field, the flux is greatest and the EMF is zero.
Physics · Electromagnetic induction: questions students ask
How many Physics · Electromagnetic induction MCQs are there?
19, each with the answer and a short explanation, across 2 topics: Faraday's and Lenz's laws, Inductance, generators and transformers. Every chapter test draws ten of them, so you can take it many times.
Is the MDCAT Physics chapter 11 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
