Question 1

Which of the following is NOT one of Maxwell’s equations in integral form?

Accepted Answer

$$\displaystyle \oint \vec{B} \cdot d\vec{s} = \mu_0$ I_{encl}$$

Question 2

An electromagnetic wave is traveling in the $$+x$$ direction. If the electric field oscillates in the $$y$$ direction, in which direction does the magnetic field oscillate?

Accepted Answer

$$+z$$ direction

Question 3

Which of the following correctly expresses the speed of light $$c in $$terms of the vacuum permittivity $$\$$epsilon_0$$ and permeability $$\$$mu_0$$?

Accepted Answer

$$c = \frac{1}{\sqrt{\mu_0$ \$$epsilon_0$$}}$$

Question 4

The ratio of the electric field amplitude to the magnetic field amplitude in an electromagnetic wave is:

Accepted Answer

$$\displaystyle \frac{E_{max}}{B_{max}} = c$$

Question 5

A radio station radiates a total average power $$P$$ equally in all directions above the ground. What is the intensity $$I$$ detected by a satellite at a distance $$R$$ from the station?

Accepted Answer

$$I = \frac{P}{2\pi R^2$}$$

Question 6

Which of the following statements about electromagnetic waves is TRUE?

Accepted Answer

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

Question 7

The Poynting vector $$\vec{S}$$ represents:

Accepted Answer

The energy per unit time per unit area carried by an electromagnetic wave.

Question 8

The average intensity $$I of an $$electromagnetic wave in terms of the maximum electric field $$E_{max} is$$:

Accepted Answer

$$I = \frac{E_{max}^2}{2\mu_0$ c}$$

Question 9

A satellite with solar panels of area $$A$$ absorbs sunlight of intensity $$I$$ perpendicular to the panels. What is the average force due to radiation pressure if all the light is absorbed?

Accepted Answer

$$F = \frac{IA}{c}$$

Question 10

Which of the following best describes the energy density $$u of an $$electromagnetic wave?

Accepted Answer

$$u = \$$epsilon_0$$ E^2$ = \frac{B^2$}{\mu_0$}$$

Question 11

If the wavelength of an electromagnetic wave is doubled, what happens to its frequency (in vacuum)?

Accepted Answer

It is halved.

Question 12

Which of the following is a correct expression for the wave number $$k of an $$electromagnetic wave?

Accepted Answer

$$k = \frac{2\pi}{\lambda}$$

Question 13

A light mill (Crookes radiometer) spins when exposed to light. What is the primary cause of this motion?

Accepted Answer

Thermal effects due to uneven heating of the vanes.

Question 14

The momentum density of an electromagnetic wave is given by:

Accepted Answer

$$\displaystyle \frac{S}{c^2$}$$

Question 15

If an electromagnetic wave is totally reflected by a surface, the radiation pressure exerted is:

Accepted Answer

$$\displaystyle P_{rad} = 2\frac{I}{c}$$

Question 16

Which of the following best describes the relationship between the electric and magnetic energy densities in an electromagnetic wave?

Accepted Answer

The electric and magnetic energy densities are equal.

Question 17

A sinusoidal electromagnetic wave has $$E_y = E_{max} \sin(kx - \omega t). $$What is the corresponding expression for $$B_z$$?

Accepted Answer

$$B_z = B_{max} \sin(kx - \omega t)$$

Question 18

Which of the following is a real-world application of electromagnetic waves in the microwave region?

Accepted Answer

Wireless data transmission (Wi-Fi)

Question 19

The time-averaged value of $$\sin^2$(kx - \omega t)$$ over one or more cycles is:

Accepted Answer

$$\frac{1}{2}$$

Electromagnetic Fields and Waves: Maxwell’s Equations, Wave Properties, and Energy Transport

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