Q: What is the speed of light in a vacuum, as given by electromagnetic theory?

$$c = 3.00 \times 10^8$\ \mathrm{m/s}$$

Question 1

Which of the following best describes the orientation of the electric and magnetic fields in an electromagnetic wave propagating in the positive x-direction?

Accepted Answer

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

Question 2

What is the speed of light in a vacuum, as given by electromagnetic theory?

Accepted Answer

$$c = 3.00 	imes 10^8$\ \mathrm{m/s}$$

Question 3

Which phenomenon explains why the frequency of light from a moving star appears shifted to an observer on Earth?

Accepted Answer

Doppler effect

Question 4

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

Accepted Answer

$$\lambda = 3.00\ \mathrm{m}$$

Question 5

Which region of the electromagnetic spectrum has the highest frequency?

Accepted Answer

Gamma rays

Question 6

What is the energy density $$u of an $$electromagnetic wave in terms of the electric field $$E$$ and the magnetic field $$B$$?

Accepted Answer

$$u = \frac{1}{2}\$$varepsilon_0$$ E^2$ + \frac{1}{2}\frac{B^2$}{\mu_0$}$$

Question 7

A beam of unpolarized light passes through a polarizer. What fraction of the original intensity is transmitted?

Accepted Answer

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

Question 8

Which of the following statements about the polarization of light is correct?

Accepted Answer

Polarized light has electric fields oscillating in a single direction.

Question 9

If the intensity of polarized light incident on a polarizer is $$I_0$$ and the angle between the light’s polarization direction and the polarizer’s axis is $$	heta$$, what is the transmitted intensity?

Accepted Answer

$$I = I_0$ \cos^2$ 	heta$$

Question 10

Which of the following is a real-world application of the radiation pressure exerted by electromagnetic waves?

Accepted Answer

The curvature of a comet’s dust tail

Question 11

A microwave oven operates at a frequency of $$2.45\ \mathrm{GHz}. $$What is the wavelength of the microwaves in the oven?

Accepted Answer

$$\lambda = 0.122\ \mathrm{m}$$

Question 12

Which of the following best explains why X-rays are useful for medical imaging?

Accepted Answer

They have high frequencies and can penetrate soft tissue but are absorbed by denser materials like bone.

Question 13

What is the relationship between the electric field $$E$$ and the magnetic field $$B in an $$electromagnetic wave in a vacuum?

Accepted Answer

$$E = cB$$

Question 14

Which of the following is NOT a correct statement about electromagnetic waves?

Accepted Answer

They require a medium to propagate.

Question 15

A beam of light is incident on a polarizer at an angle of $$60^\circ to $$the axis of the polarizer. If the initial intensity is $$I_0$$, what is the transmitted intensity?

Accepted Answer

$$I = I_0$ \cos^2$ 60^\circ = 0.25 I_0$

Question 16

Which of the following best describes the effect of the Doppler effect on electromagnetic waves?

Accepted Answer

It changes the frequency observed when the source and observer are moving relative to each other.

Question 17

Which of the following is a consequence of the energy carried by electromagnetic waves?

Accepted Answer

They can exert a force and pressure on objects.

Question 18

Which of the following is true about the electromagnetic spectrum?

Accepted Answer

Gamma rays have the shortest wavelength.

Question 19

A scientist wants to sterilize medical equipment using electromagnetic waves. Which type should they use?

Accepted Answer

Gamma rays

Question 20

Which of the following is a correct statement about the Law of Malus?

Accepted Answer

The transmitted intensity through a polarizer is proportional to the square of the cosine of the angle between the light’s polarization and the polarizer’s axis.

Electromagnetic Waves – Physics with Calculus Study Notes

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