Q: Which of the following is the correct differential form of Gauss's law for electricity, as given by Maxwell's equations?

$$ \nabla \cdot \vec{E} = \frac{\rho}{\varepsilon_0} $$

Q: Which of the following best describes the Poynting vector $$\vec{S} in $$the context of electromagnetic waves?

$$ \vec{S} = \frac{1}{\mu_0} \vec{E} \times \vec{B} $$

Q: A radio station broadcasts at a frequency of $$100$$ MHz. What is the wavelength of the radio waves it emits?

$$ \lambda = \frac{c}{f} = \frac{3.0 \times 10^8 \ \text{m/s}}{1.0 \times 10^8 \ \text{Hz}} = 3.0 \ \text{m} $$

Question 1

Which of the following is the correct differential form of Gauss's law for electricity, as given by Maxwell's equations?

Accepted Answer

$$ 
abla \cdot \vec{E} = \frac{ho}{\varepsilon_0} $$

Question 2

Why did Maxwell introduce the concept of displacement current in the Ampère-Maxwell law?

Accepted Answer

To account for the changing electric field in regions where there is no conduction current, such as between the plates of a charging capacitor.

Question 3

Consider a parallel-plate capacitor being charged by a current $$I. $$According to Maxwell's correction, what is the expression for the displacement current $$I_d$$ between the plates?

Accepted Answer

$$ I_d = \varepsilon_0 \frac{d\Phi_E}{dt} $$

Question 4

Which of the following statements about electromagnetic waves in free space is correct?

Accepted Answer

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

Question 5

What is the speed of electromagnetic waves in vacuum, according to Maxwell's equations?

Accepted Answer

$$ c = \frac{1}{\sqrt{\varepsilon_0 \mu_0}} $$

Question 6

A sinusoidal electromagnetic wave is traveling in the $$+x$$ direction. If the electric field is given by $$\vec{E} = E_0$ \sin(kx - \omega t) \hat{y}$$, what is the corresponding magnetic field?

Accepted Answer

$$ \vec{B} = \frac{E_0}{c} \sin(kx - \omega t) \hat{z} $$

Question 7

Which of the following best describes the Poynting vector $$\vec{S} in $$the context of electromagnetic waves?

Accepted Answer

$$ \vec{S} = \frac{1}{\mu_0} \vec{E} 	imes \vec{B} $$

Question 8

Which of the following is NOT a consequence of Maxwell's equations?

Accepted Answer

The existence of magnetic monopoles.

Question 9

A radio station broadcasts at a frequency of $$100$$ MHz. What is the wavelength of the radio waves it emits?

Accepted Answer

$$ \lambda = \frac{c}{f} = \frac{3.0 	imes 10^8 \ 	ext{m/s}}{1.0 	imes 10^8 \ 	ext{Hz}} = 3.0 \ 	ext{m} $$

Question 10

Which of the following best explains why electromagnetic waves can travel through the vacuum of space?

Accepted Answer

They are self-sustaining due to the mutual induction of electric and magnetic fields.

Question 11

In the context of the electromagnetic spectrum, which type of wave has the shortest wavelength?

Accepted Answer

Gamma rays

Question 12

A satellite dish receives signals from a satellite. Which region of the electromagnetic spectrum do these signals most likely belong to?

Accepted Answer

Microwaves

Question 13

Which of the following is the correct integral form of Faraday's law of induction?

Accepted Answer

$$ \oint \vec{E} \cdot d\vec{l} = -\frac{d\Phi_B}{dt} $$

Question 14

If the electric field in an electromagnetic wave is doubled, what happens to the energy density $$u of $$the wave?

Accepted Answer

It increases by a factor of 4.

Question 15

Which of the following best describes the orientation of the electric and magnetic fields in a plane electromagnetic wave propagating in the $$x-$$direction?

Accepted Answer

The electric field is along $$y$$, the magnetic field is along $$z$$, and both are perpendicular to $$x.$$

Question 16

A cell phone communicates using electromagnetic waves. Which property of these waves allows information to be transmitted over long distances?

Accepted Answer

They can propagate through the atmosphere and vacuum at the speed of light.

Question 17

Which of the following is a correct statement about the magnetic flux through a closed surface, according to Maxwell's equations?

Accepted Answer

It is always zero, indicating the absence of magnetic monopoles.

Question 18

Which equation describes the wave nature of the electric field in free space, derived from Maxwell's equations?

Accepted Answer

$$ 
abla^2 \vec{E} = \varepsilon_0 \mu_0 \frac{\partial^2 \vec{E}}{\partial t^2} $$

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