Question 1

Which of the following best describes Faraday's Law of Induction?

Accepted Answer

The induced emf in a circuit is proportional to the rate of change of magnetic flux through the circuit, with a direction given by Lenz's Law.

Question 2

A circular loop of wire is placed in a region where the magnetic field is increasing into the page. According to Lenz's Law, what is the direction of the induced current?

Accepted Answer

Counterclockwise, to oppose the increase in magnetic flux into the page.

Question 3

Which equation correctly expresses Faraday’s Law of Induction for a single loop?

Accepted Answer

$$ \mathcal{E} = -\frac{d\Phi_B}{dt} $$

Question 4

A square coil is pulled out of a uniform magnetic field at constant speed. What is the direction of the induced current as the coil leaves the field?

Accepted Answer

The current is clockwise to oppose the decrease in flux.

Question 5

Which of the following is NOT a requirement for electromagnetic induction to occur in a loop of wire?

Accepted Answer

A steady magnetic field through the loop.

Question 6

A metal rod of length $$L$$ moves with velocity $$v$$ perpendicular to a uniform magnetic field $$B. $$What is the induced emf across the ends of the rod?

Accepted Answer

$$ \mathcal{E} = BLv $$

Question 7

Which device uses electromagnetic induction to convert mechanical energy into electrical energy?

Accepted Answer

AC Generator

Question 8

A transformer has 100 turns on the primary coil and 400 turns on the secondary coil. If the input voltage is $$120\ \mathrm{V}$$, what is the output voltage (assuming 100% efficiency)?

Accepted Answer

$$480\ \mathrm{V}$$

Question 9

Which of the following best explains the phenomenon of eddy currents?

Accepted Answer

Currents induced in bulk conductors moving through a changing magnetic field, which oppose the motion and cause magnetic damping.

Question 10

Which of the following is the correct transformer equation relating the voltages and number of turns in the coils?

Accepted Answer

$$ \frac{V_s}{V_p} = \frac{N_s}{N_p} $$

Question 11

A loop of wire is shrinking in a uniform magnetic field pointing into the page. What is the direction of the induced current?

Accepted Answer

Clockwise, to increase the flux.

Question 12

Which of the following statements about the split-ring commutator in a DC generator is correct?

Accepted Answer

It ensures that the output current always flows in the same direction, producing direct current.

Question 13

If the magnetic flux through a coil changes from $$0.2\ \mathrm{Wb} to$$ $$0.1\ \mathrm{Wb} in$$ $$0.05\ \mathrm{s}$$, what is the magnitude of the average induced emf?

Accepted Answer

$$2\ \mathrm{V}$$

Question 14

Which of the following best describes Lenz’s Law?

Accepted Answer

The induced emf always acts to oppose the change in magnetic flux.

Question 15

A generator coil rotates in a magnetic field, producing an emf described by $$ \mathcal{E}(t) = \mathcal{E}_0 \sin(\omega t) . $$What type of current is produced?

Accepted Answer

Alternating current (AC)

Question 16

Which of the following is a real-world application of electromagnetic induction?

Accepted Answer

Wireless charging of smartphones

Question 17

A transformer is used to step down the voltage from $$240\ \mathrm{V} to$$ $$24\ \mathrm{V}. If $$the primary coil has 600 turns, how many turns does the secondary coil have?

Accepted Answer

60

Question 18

Which of the following integrals expresses the general form of Faraday’s Law relating electric and magnetic fields?

Accepted Answer

$$ \oint \vec{E} \cdot d\vec{s} = -\frac{d\Phi_B}{dt} $$

Electromagnetic Induction: Faraday’s Law, Lenz’s Law, and Applications

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