Question 1

Which equation is used to calculate the magnitude of the induced emf in a conducting loop due to a changing magnetic flux?

Accepted Answer

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

Question 2

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 decreases at a constant rate, what is the direction of the induced current?

Accepted Answer

Clockwise, as viewed from above

Question 3

Which of the following best describes the physical meaning of magnetic flux $$\Phi_B$$ through a surface?

Accepted Answer

The total number of magnetic field lines passing through the surface

Question 4

A transformer is used to step down the voltage from 120 V to 12 V. If the primary coil has 600 turns, how many turns must the secondary coil have?

Accepted Answer

60

Question 5

Which of the following statements about electromagnetic waves is correct?

Accepted Answer

They consist of oscillating electric and magnetic fields perpendicular to each other and to the direction of propagation.

Question 6

If the magnetic flux through a loop changes from $$0.5\ \mathrm{Wb} to$$ $$0.1\ \mathrm{Wb} in$$ $$0.2\ \mathrm{s}$$, what is the magnitude of the average induced emf?

Accepted Answer

$$0.4\ \mathrm{V}$$

Question 7

Which of the following is NOT a way to increase the induced emf in a coil?

Accepted Answer

Decrease the resistance of the coil

Question 8

A solenoid with $$N$$ turns and length $$l$$ carries a current $$I. $$What is the expression for the magnetic field inside the solenoid?

Accepted Answer

$$B = \mu_0$ \frac{N}{l} I$$

Question 9

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

Accepted Answer

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

Question 10

Which of the following best explains why the induced current in a loop opposes the change in magnetic flux through the loop?

Accepted Answer

Lenz's Law

Question 11

An electromagnetic wave in vacuum has an electric field amplitude $$E_0. $$What is the amplitude of the associated magnetic field $$B_0$$?

Accepted Answer

$$B_0$$ = \frac{$$E_0$$}{c}$$

Question 12

A coil with 200 turns encloses an area of $$0.05\ \mathrm{m}^2. $$The magnetic field through the coil changes from $$0.3\ \mathrm{T} to$$ $$-0.2\ \mathrm{T} in$$ $$0.1\ \mathrm{s}. $$What is the magnitude of the average induced emf?

Accepted Answer

$$100\ \mathrm{V}$$

Question 13

Which of the following is true about the energy carried by an electromagnetic wave?

Accepted Answer

It is equally shared between the electric and magnetic fields.

Question 14

A radio station broadcasts at a frequency of $$100\ \mathrm{MHz}. $$What is the wavelength of the radio waves in air?

Accepted Answer

$$3\ \mathrm{m}$$

Question 15

Which of the following is a correct statement about the speed of electromagnetic waves in vacuum?

Accepted Answer

It is given by $$c = \frac{1}{\sqrt{\mu_0$ \$$epsilon_0$$}}$$

Question 16

A patient undergoes an MRI scan, which uses strong magnetic fields. If the field changes rapidly, what physical principle could induce currents in the patient's body?

Accepted Answer

Faraday's Law of Induction

Question 17

A power plant uses a generator to convert mechanical energy into electrical energy. Which principle explains the operation of the generator?

Accepted Answer

Electromagnetic induction

Question 18

A wire loop is rotated in a uniform magnetic field at a constant angular velocity. What is the form of the induced emf as a function of time?

Accepted Answer

$$\mathcal{E}(t) = \mathcal{E}_0 \sin(\omega t)$$

Question 19

Which of the following best describes the role of the core in a transformer?

Accepted Answer

It increases the magnetic flux linkage between the coils.

Electromagnetic Induction and Electromagnetic Waves: Exam 3 Study Guide

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