Question 1

A square coil of side $$5\ \mathrm{cm}$$ with $$100$$ turns is pulled out of a $$0.6\ \mathrm{T}$$ magnetic field in $$0.10\ \mathrm{s}. $$What is the magnitude of the average induced emf in the coil?

Accepted Answer

$$1.5\ \mathrm{V}$$

Question 2

Which of the following best describes Lenz’s Law?

Accepted Answer

The induced current flows in a direction that creates a magnetic field that opposes the change in flux through the loop.

Question 3

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

Accepted Answer

$$B\ell v$$

Question 4

A generator coil with $$N$$ turns, area $$A$$, rotates in a uniform magnetic field $$B$$ with angular speed $$\omega. $$What is the expression for the maximum emf generated?

Accepted Answer

$$NAB\omega$$

Question 5

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

Accepted Answer

All of the above

Question 6

A loop of wire is shrinking in area in a region where the magnetic field points into the page. According to Lenz’s Law, what is the direction of the induced current as viewed from above?

Accepted Answer

Clockwise

Question 7

A long solenoid has $$n$$ turns per meter and carries a current decreasing at a rate $$dI/dt. $$What is the magnitude of the induced electric field at a distance $$r$$ from the axis inside the solenoid?

Accepted Answer

$$E = \frac{\mu_0$ n r}{2} \frac{dI}{dt}$$

Question 8

Which statement about induced electric fields is correct?

Accepted Answer

Induced electric fields form closed loops and are nonconservative.

Question 9

A slide-wire generator consists of a rod of length $$\ell$$ moving at speed $$v$$ perpendicular to a magnetic field $$B. If $$the resistance of the loop is $$R$$, what is the power dissipated in the loop?

Accepted Answer

$$P = \frac{B^2$ \$$ell^2$$ v^2$}{R}$$

Question 10

Which of the following best explains why an induction stove heats a metal pan but not an insulator?

Accepted Answer

Eddy currents are induced in the metal, causing resistive heating.

Question 11

A bar magnet is moved toward a coil of wire. What is the direction of the induced current in the coil as seen from the approaching magnet?

Accepted Answer

Counterclockwise

Question 12

Which of the following is NOT a way to change the magnetic flux through a loop?

Accepted Answer

Keeping the loop stationary in a constant magnetic field

Question 13

A motor is first turned on and draws a large current, causing lights to dim briefly. What is the main reason for this effect?

Accepted Answer

The back emf is initially small, so the current is large.

Question 14

Which equation correctly expresses Faraday’s Law for a coil with $$N$$ turns?

Accepted Answer

$$\epsilon = -N \frac{d\Phi_B}{dt}$$

Question 15

Which of the following is a consequence of Lenz’s Law?

Accepted Answer

Energy conservation is maintained in electromagnetic induction.

Question 16

A coil with $$N$$ turns and resistance $$R is $$pulled out of a magnetic field at constant speed. What is the force required to keep the coil moving at constant speed?

Accepted Answer

$$F = N I \ell B$$

Question 17

Which of the following statements about displacement current is correct?

Accepted Answer

It accounts for the changing electric flux between capacitor plates.

Question 18

Which Maxwell equation describes how a changing magnetic field induces an electric field?

Accepted Answer

$$
abla 	imes \vec{E} = -\frac{\partial \vec{B}}{\partial t}$$

Question 19

Which of the following is a practical use of eddy currents?

Accepted Answer

Braking systems in roller coasters

Electromagnetic Induction and Its Applications

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