Question 1

Which of the following statements best describes the relationship between the electric and magnetic fields in an electromagnetic wave propagating in vacuum?

Accepted Answer

The electric and magnetic fields are perpendicular to each other and to the direction of propagation.

Question 2

According to Maxwell’s equations, what is the speed of electromagnetic waves in vacuum, and how is it related to the fundamental constants of electromagnetism?

Accepted Answer

The speed is $$c = \frac{1}{\sqrt{\mu_0$ \$$varepsilon_0$$}}$$, where $$\mu_0$ is the permeability and $$\$$varepsilon_0 is $$the permittivity of free space.

Question 3

A sinusoidal electromagnetic wave is traveling in the positive x-direction. If the electric field oscillates in the y-direction, in which direction does the magnetic field oscillate?

Accepted Answer

In the z-direction

Question 4

Which of the following best describes the energy flow in an electromagnetic wave?

Accepted Answer

The energy flow is described by the Poynting vector $$\vec{S} = \frac{1}{\mu_0$} \vec{E} 	imes \vec{B}$$, which points in the direction of wave propagation.

Question 5

What is the relationship between the magnitudes of the electric and magnetic fields in a plane electromagnetic wave in vacuum?

Accepted Answer

$$E = cB$$

Question 6

A solar panel in space receives electromagnetic radiation from the Sun. If the intensity of sunlight is $$I$$, what is the radiation pressure $$P_{rad} on $$the panel if it perfectly absorbs the light?

Accepted Answer

$$P_{rad} = \frac{I}{c}$$

Question 7

Which of the following is NOT a property of electromagnetic waves?

Accepted Answer

They require a medium to propagate.

Question 8

A radio wave has a frequency of $$1 	imes 10^8$ Hz. What is its wavelength in vacuum?

Accepted Answer

$$\lambda = 3 m$$

Question 9

Which region of the electromagnetic spectrum has the shortest wavelength?

Accepted Answer

Gamma rays

Question 10

If the speed of light in a material is $$2 	imes 10^8$ m/s, what is the index of refraction n$ of the material?

Accepted Answer

$$n = 1.5$$

Question 11

Which color of visible light has the highest frequency?

Accepted Answer

Violet

Question 12

A standing electromagnetic wave is formed between a perfect conductor and a point at $$x = \lambda. $$What is true at $$x = \lambda$$?

Accepted Answer

The electric field is zero (nodal plane), and the magnetic field is maximum (antinode).

Question 13

Which law describes the electric field produced by a changing magnetic field?

Accepted Answer

Faraday’s law

Question 14

What is the time-averaged intensity $$I of a $$sinusoidal electromagnetic wave in vacuum in terms of the maximum electric field $$E_{max}$$?

Accepted Answer

$$I = \frac{c \$$varepsilon_0$$}{2} E_{max}^2$$

Question 15

Which of the following best explains why electromagnetic waves can propagate through empty space?

Accepted Answer

A changing electric field produces a magnetic field, and a changing magnetic field produces an electric field, allowing the wave to sustain itself.

Question 16

A point charge oscillates in simple harmonic motion. What is the result according to Maxwell’s theory?

Accepted Answer

Electromagnetic waves are emitted, radiating energy away from the charge.

Question 17

Which of the following is a correct expression for the energy density $$u in an $$electromagnetic wave in vacuum?

Accepted Answer

$$u = \$$varepsilon_0$$ E^2$

Question 18

Which of the following best describes the polarization of an electromagnetic wave?

Accepted Answer

Polarization refers to the direction of the electric field oscillation.

Question 19

If an electromagnetic wave passes through a small area far from its source, how can it be treated?

Accepted Answer

It can be treated as a plane wave.

Question 20

Which of the following is the correct right-hand rule for determining the direction of propagation of an electromagnetic wave?

Accepted Answer

Point your thumb in the direction of propagation, curl your fingers from $$\vec{E} to$$ $$\vec{B}$$, and your thumb points in the direction of $$\vec{E} 	imes \vec{B}.$$

Electromagnetic Waves: Maxwell’s Theory, Properties, and Applications

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