Question 1

A circular loop of wire with area $$A is $$placed in a uniform magnetic field $$B$$ perpendicular to the plane of the loop. If the magnetic field increases linearly with time, which of the following correctly describes the induced emf in the loop according to Faraday’s Law?

Accepted Answer

The induced emf is given by $$\displaystyle \mathcal{E} = -A \frac{dB}{dt}.$$

Question 2

A bar magnet is moved rapidly into a coil connected to a sensitive ammeter. Which of the following statements best explains the observed current in the coil?

Accepted Answer

A current is induced because the magnetic flux through the coil is changing.

Question 3

A rectangular loop of wire is pulled at constant velocity $$v$$ out of a region with a uniform magnetic field $$B ($$perpendicular to the loop). If the width of the loop is $$w$$, what is the magnitude of the induced emf as the loop leaves the field?

Accepted Answer

$$\displaystyle \mathcal{E} = Bwv$$

Question 4

Which of the following best describes Lenz’s Law?

Accepted Answer

The induced emf produces a current whose magnetic field opposes the change in magnetic flux.

Question 5

A transformer has 100 turns on its primary coil and 1000 turns on its secondary coil. If the input voltage is $$120\ \mathrm{V} AC$$, what is the output voltage (assuming ideal transformer)?

Accepted Answer

$$\displaystyle 1200\ \mathrm{V}$$

Question 6

A hospital uses a transformer to step down the voltage from $$240\ \mathrm{V} to$$ $$24\ \mathrm{V}$$ for a medical device. If the primary coil has 600 turns, how many turns should the secondary coil have?

Accepted Answer

$$\displaystyle 60$$

Question 7

Which of the following statements about eddy currents is correct?

Accepted Answer

Eddy currents are induced in bulk conductors and can cause energy loss as heat.

Question 8

A microphone works by electromagnetic induction. Which of the following best describes the process?

Accepted Answer

A vibrating membrane moves a coil in a magnetic field, inducing an emf.

Question 9

In an LR circuit, what happens to the current immediately after the switch is closed?

Accepted Answer

The current starts at zero and increases gradually.

Question 10

Which of the following is true about the energy stored in an inductor with inductance $$L$$ carrying current $$I$$?

Accepted Answer

$$\displaystyle U = \frac{1}{2}LI^2$

Question 11

A 60 Hz AC circuit contains a resistor, inductor, and capacitor in series. If the inductive reactance equals the capacitive reactance, what is the effect on the circuit?

Accepted Answer

The impedance is minimized and the current is maximized (resonance).

Question 12

Which of the following best explains why transformers do not work with direct current (DC)?

Accepted Answer

DC produces a constant magnetic field, so no emf is induced in the secondary coil.

Question 13

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

Accepted Answer

$$\displaystyle \mathcal{E}_{	ext{max}} = NAB\omega$$

Question 14

In an AC circuit, the current through a capacitor:

Accepted Answer

Leads the voltage by 90 degrees.

Question 15

A ground fault circuit interrupter (GFCI) is designed to:

Accepted Answer

Interrupt the circuit if a difference in current is detected between the hot and neutral wires.

Question 16

Which of the following equations gives the mutual inductance $$M$$ between two coils, where $$\mathcal{E}_2 is $$the emf induced in coil 2 by a changing current $$I_1 in $$coil 1?

Accepted Answer

$$\displaystyle \mathcal{E}_2 = -M \frac{dI_1$}{dt}$$

Question 17

A hard drive stores information by:

Accepted Answer

Magnetizing small regions on a ferromagnetic coating.

Question 18

In a series LRC circuit, the impedance $$Z is $$given by:

Accepted Answer

$$\displaystyle Z = \sqrt{R^2$ + (X_L - X_C)^2$}$$

Question 19

A patient’s blood flow is measured using electromagnetic induction. If the blood vessel has diameter $$d$$ and blood moves at velocity $$v$$ perpendicular to a magnetic field $$B$$, what is the induced emf?

Accepted Answer

$$\displaystyle \mathcal{E} = Bdv$$

Question 20

Which of the following best describes the function of RAM in a computer?

Accepted Answer

It stores binary information as electric charges or voltages, but loses data when power is off.

Chpt 21

스터디 가이드 - 연습 문제

학습 가이드 - 플래시카드