Question 1

A circular coil with 100 turns and a radius of 10 cm is placed in a uniform magnetic field of 0.5 T. The plane of the coil is perpendicular to the field. If the coil is rotated by 90° in 0.2 s, what is the average induced emf in the coil?

Accepted Answer

$$\displaystyle 0.39\ \mathrm{V}$$

Question 2

Which of the following best describes Lenz’s Law?

Accepted Answer

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

Question 3

A metal rod of length $$0.5\ \mathrm{m}$$ moves at a constant speed of $$3\ \mathrm{m/s}$$ perpendicular to a $$0.8\ \mathrm{T}$$ magnetic field. What is the emf induced across the ends of the rod?

Accepted Answer

$$\displaystyle 1.2\ \mathrm{V}$$

Question 4

A transformer has a primary coil with 200 turns and a secondary coil with 50 turns. If the input voltage is $$120\ \mathrm{V}$$, what is the output voltage?

Accepted Answer

$$\displaystyle 30\ \mathrm{V}$$

Question 5

A 500-turn coil with an area of $$0.04\ \mathrm{m}^2 is $$rotated at $$60\ \mathrm{rev/s} in a$$ $$0.2\ \mathrm{T}$$ magnetic field. What is the maximum emf generated?

Accepted Answer

$$\displaystyle 1,507\ \mathrm{V}$$

Question 6

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

Accepted Answer

Magnetic braking in roller coasters

Question 7

A solenoid has a self-inductance of $$2.0\ \mathrm{H}$$ and carries a current of $$3.0\ \mathrm{A}. $$How much energy is stored in its magnetic field?

Accepted Answer

$$\displaystyle 9.0\ \mathrm{J}$$

Question 8

If the current in a coil changes from $$5.0\ \mathrm{A} to$$ $$0\ \mathrm{A} in$$ $$0.01\ \mathrm{s}$$ and the coil has a self-inductance of $$0.2\ \mathrm{H}$$, what is the average induced emf?

Accepted Answer

$$\displaystyle 100\ \mathrm{V}$$

Question 9

A 100-turn coil is pulled from a $$0.6\ \mathrm{T}$$ magnetic field at constant speed. The coil is square with sides $$5.0\ \mathrm{cm}$$ and takes $$0.1\ \mathrm{s} to $$exit the field. What is the induced emf?

Accepted Answer

$$\displaystyle 1.5\ \mathrm{V}$$

Question 10

Which of the following statements about transformers is correct?

Accepted Answer

Transformers work only with alternating current (AC).

Question 11

A plug-in transformer supplies $$9.00\ \mathrm{V} to a $$device. If the input voltage is $$120\ \mathrm{V}$$ and the primary coil has 400 turns, how many turns are in the secondary coil?

Accepted Answer

$$\displaystyle 30$$

Question 12

Which of the following best describes the energy stored in an inductor with inductance $$L$$ and current $$I$$?

Accepted Answer

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

Question 13

A 25.0 mH inductor has a resistance of $$4\ \Omega. $$What is the time constant $$	au of $$the LR circuit?

Accepted Answer

$$\displaystyle 6.25 	imes 10$$^{-3}$$\ \mathrm{s}$$

Question 14

Which of the following is NOT a consequence of Faraday’s Law?

Accepted Answer

A changing electric field produces a magnetic field.

Question 15

A generator coil rotates in a magnetic field at a constant angular velocity $$\omega. $$When is the induced emf at its maximum?

Accepted Answer

When the plane of the coil is parallel to the magnetic field ($$	heta = 90^\circ)$$

Question 16

A mutual inductance of $$5.00\ \mathrm{mH}$$ exists between two coils. If the current in one coil drops from $$2.00\ \mathrm{A} to$$ $$0 in$$ $$30.0\ \mathrm{ms}$$, what is the induced emf in the other coil?

Accepted Answer

$$\displaystyle 0.333\ \mathrm{V}$$

Question 17

Which of the following best describes the function of a GFCI (Ground Fault Circuit Interrupter) in terms of electromagnetic induction?

Accepted Answer

It detects differences in current between the hot and neutral wires, inducing a voltage that triggers a circuit breaker.

Question 18

Which of the following is the correct formula for the impedance $$Z of a $$series LRC AC circuit?

Accepted Answer

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

Chapter 21: Electromagnetic Induction and Faraday’s Law – Study Notes

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