Question 1

Which of the following best explains why closing or opening the switch in Faraday's iron ring experiment (see image 1) causes a momentary current in the secondary coil, but no current flows when the switch remains closed?

Accepted Answer

A current is only induced when the magnetic field through the secondary coil is changing, not when it is constant.

Question 2

A straight conductor of length $$l$$ moves with velocity $$\vec{v}$$ perpendicular to a uniform magnetic field $$\vec{B} ($$see image 3). What is the magnitude of the motional emf generated across the conductor?

Accepted Answer

$$\mathcal{E} = v l B$$

Question 3

In the scenario shown in image 5, what condition must be met for the net force on a charge in the conductor to be zero?

Accepted Answer

$$E = v B$$

Question 4

A conducting bar slides to the right on a U-shaped rail in a uniform magnetic field directed into the page (see image 9). What is the direction of the induced current in the loop?

Accepted Answer

Counterclockwise

Question 5

If the resistance of the circuit in the sliding wire setup is $$R$$, what is the expression for the induced current?

Accepted Answer

$$I = \frac{v l B}{R}$$

Question 6

A metal sheet is pulled through a magnetic field, inducing eddy currents (see image 15). What is the direction of the magnetic force on the sheet due to these eddy currents?

Accepted Answer

Opposite to the direction of motion

Question 7

The magnetic flux through a loop of area $$A in a $$uniform magnetic field $$B at an $$angle $$	heta to $$the area vector is given by:

Accepted Answer

$$\Phi_m = A B \cos 	heta$$

Question 8

According to Lenz's law, what is the direction of the induced current when a bar magnet is pushed into a loop with its north pole first (see image 21)?

Accepted Answer

Counterclockwise, to oppose the increase in downward flux

Question 9

Which of the following statements about Faraday's law is correct?

Accepted Answer

An emf is induced around a closed loop if the magnetic flux through the loop changes.

Question 10

A circular loop of wire with radius $$r = r_0$ e$$^{-a t}$$ is shrinking in a uniform magnetic field B$ pointing out of the page. What is the expression for the induced emf at time t$?

Accepted Answer

$$\mathcal{E} = 2 \pi B a r_0$^2 e$$^{-2 a t}$$

Question 11

Which of the following best describes the difference between Coulomb and non-Coulomb electric fields?

Accepted Answer

Coulomb fields begin and end on charges, while non-Coulomb fields form closed loops and are induced by changing magnetic fields.

Question 12

A transformer has $$N_1$$ turns in the primary coil and $$N_2$$ turns in the secondary coil. If the input voltage is $$V_1$$, what is the output voltage $$V_2$$?

Accepted Answer

$$V_2$$ = \frac{$$N_2$$}{$$N_1$$} $$V_1$$

Question 13

Which of the following is a direct consequence of Maxwell's equations regarding electromagnetic waves?

Accepted Answer

Electromagnetic waves travel in vacuum at speed $$c = \frac{1}{\sqrt{\$$epsilon_0$$ \mu_0$}}$$

Question 14

A 20 cm × 20 cm square loop lies in the xy-plane. A magnetic field $$B = 0.80 y^2$ t (in $$tesla, $$y in $$meters, $$t in $$seconds) points along the z-axis. What is the induced emf in the loop at $$t = 0.50 s$$?

Accepted Answer

$$0.11 V$$

Question 15

Which of the following best describes the operation of a generator?

Accepted Answer

It converts mechanical energy into electrical energy by inducing an emf through motion in a magnetic field.

Question 16

A metal detector works by detecting changes in the induced current in the receiver coil. What causes this change when a metal object is present?

Accepted Answer

Eddy currents induced in the metal alter the net magnetic field at the receiver coil.

Question 17

Which of the following is NOT a property of electromagnetic waves as described by Maxwell's equations?

Accepted Answer

The electric and magnetic fields are always parallel to each other.

Electromagnetic Induction and Faraday’s Law

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