Question 1

A sinusoidal electromagnetic wave has an electric field whose rms value is 100 V/m.What is the instantaneous rate S of energy flow for this wave?

Accepted Answer

A) 1.7 *10-4 W/m2 
B) 13 W/m2 
C) 27 W/m2 
D) 1.0 * 105 W/m2 
E) 4.0 * 1010 W/m2 
A) 1.7 *10-4 W/m2 
B) 13 W/m2 
C) 27 W/m2 
D) 1.0 * 105 W/m2 
E) 4.0 * 1010 W/m2

Question 2

At a certain point and a certain time the electric field of an electromagnetic wave is in the negative z direction and the magnetic field is in the positive y direction.Which of the following statements is true?

Accepted Answer

A) Energy is being transported in the positive x direction but half a cycle later, when the electric field is in the opposite direction, it will be transported in the negative x direction. 
B) Energy is being transported in the positive x direction and half a cycle later, when the electric field is in the opposite direction, it will still be transported in the positive x direction. 
C) Energy is being transported in the negative x direction but half a cycle later, when the electric field is in the opposite direction, it will be transported in the positive x direction. 
D) Energy is being transported in the negative x direction and half a cycle later, when the electric field is in the opposite direction, it will still be transported in the negative x direction. 
E) None of the above is true. 
A) Energy is being transported in the positive x direction but half a cycle later, when the electric field is in the opposite direction, it will be transported in the negative x direction. 
B) Energy is being transported in the positive x direction and half a cycle later, when the electric field is in the opposite direction, it will still be transported in the positive x direction. 
C) Energy is being transported in the negative x direction but half a cycle later, when the electric field is in the opposite direction, it will be transported in the positive x direction. 
D) Energy is being transported in the negative x direction and half a cycle later, when the electric field is in the opposite direction, it will still be transported in the negative x direction. 
E) None of the above is true.

Question 3

If the electric field in a plane electromagnetic wave is along the y axis and its magnitude is given by Em sin (kx + $ \omega $t)in SI units, then the magnetic field is along the z axis and its magnitude is given by:

Accepted Answer

A) (Em/c)cos (kx + $ \omega $t) 
B) -(Em/c)cos (kx + $ \omega $t) 
C) (Em/c)sin (kx + $ \omega $t) 
D) -(Em/c)sin (kx + $ \omega $t) 
E) Em cos (kx + $ \omega $t) 
A) (Em/c)cos (kx + $ \omega $t) 
B) -(Em/c)cos (kx + $ \omega $t) 
C) (Em/c)sin (kx + $ \omega $t) 
D) -(Em/c)sin (kx + $ \omega $t) 
E) Em cos (kx + $ \omega $t)

Question 4

A pole stands in a river, half in and half out of the water.Another pole of the same length stands vertically on the shore at a place where the ground is level.The shadow cast by the pole in the river on the river bottom is:

Accepted Answer

A) slightly longer than the shadow of the pole on land 
B) much longer than the shadow of the pole on land 
C) shorter than the shadow of the pole on land 
D) shorter than the shadow of the pole on land if the sun is high and longer if the sun is low 
E) the same length as the shadow of the pole on land 
A) slightly longer than the shadow of the pole on land 
B) much longer than the shadow of the pole on land 
C) shorter than the shadow of the pole on land 
D) shorter than the shadow of the pole on land if the sun is high and longer if the sun is low 
E) the same length as the shadow of the pole on land

Question 5

An electromagnetic wave is transporting energy in the negative y direction.At one point and one instant the magnetic field is in the positive x direction.The electric field at that point and instant is:

Accepted Answer

A) positive y direction 
B) negative y direction 
C) positive z direction 
D) negative z direction 
E) negative x direction 
A) positive y direction 
B) negative y direction 
C) positive z direction 
D) negative z direction 
E) negative x direction

Question 6

The electric field in unpolarized light:

Accepted Answer

A) has no direction at any time 
B) rotates rapidly 
C) is always parallel to the direction of propagation 
D) can be in any direction perpendicular to the direction of propagation 
E) remains along the same line but reverses direction randomly and often 
A) has no direction at any time 
B) rotates rapidly 
C) is always parallel to the direction of propagation 
D) can be in any direction perpendicular to the direction of propagation 
E) remains along the same line but reverses direction randomly and often

Question 7

The magnetic field in a sinusoidal light wave has an amplitude of 3.3 * 10-7 T.The intensity of the wave is:

Accepted Answer

A) 1.7 *10-4 W/m2 
B) 13 W/m2 
C) 27 W/m2 
D) 1.0 * 105 W/m2 
E) 4.0 * 1010 W/m2 
A) 1.7 *10-4 W/m2 
B) 13 W/m2 
C) 27 W/m2 
D) 1.0 * 105 W/m2 
E) 4.0 * 1010 W/m2

Question 8

The diagram shows total internal reflection.Which of the following statements is NOT true?

Accepted Answer

A) angle AON is the angle of incidence 
B) angle AON = angle BON 
C) angle AON must be the critical angle 
D) the speed of light in medium II is greater than that in medium I 
E) if angle AON were increased, there would still be total internal reflection 
A) angle AON is the angle of incidence 
B) angle AON = angle BON 
C) angle AON must be the critical angle 
D) the speed of light in medium II is greater than that in medium I 
E) if angle AON were increased, there would still be total internal reflection

Question 9

A sinusoidal electromagnetic wave with an electric field amplitude of 100 V/m is incident normally on a surface with an area of 1 cm2 and is completely absorbed.The energy absorbed in 10 s is:

Accepted Answer

A) 1.3 mJ 
B) 13 mJ 
C) 27 mJ 
D) 130 mJ 
E) 270 mJ 
A) 1.3 mJ 
B) 13 mJ 
C) 27 mJ 
D) 130 mJ 
E) 270 mJ

Question 10

Maxwell's equations predict that the speed of electromagnetic waves in free space is given by:

Accepted Answer

A) µ0ε0 
B) (µ0ε0)1/2 
C) 1/ µ0ε0 
D) 1/(µ0ε0)1/2 
E) 1/(µ0ε0)2 
A) µ0ε0 
B) (µ0ε0)1/2 
C) 1/ µ0ε0 
D) 1/(µ0ε0)1/2 
E) 1/(µ0ε0)2

Question 11

The illustration shows total internal reflection taking place in a piece of glass.The index of refraction of this glass:

Accepted Answer

A) is at least 2.0 
B) is at most 2.0 
C) is at least 1.15 
D) is at most 1.15 
E) cannot be calculated from the given data 
A) is at least 2.0 
B) is at most 2.0 
C) is at least 1.15 
D) is at most 1.15 
E) cannot be calculated from the given data

Question 12

The diagram shows the passage of a ray of light from air into a substance X.The index of refraction of X is:

Accepted Answer

A) 0.53 
B) 0.82 
C) 1.2 
D) 1.9 
E) 3.0 
A) 0.53 
B) 0.82 
C) 1.2 
D) 1.9 
E) 3.0

Question 13

Radio waves of wavelength 3 cm have a frequency of:

Accepted Answer

A) 1 MHz 
B) 9 MHz 
C) 100 MHz 
D) 900 MHz 
E) 10,000 MHz 
A) 1 MHz 
B) 9 MHz 
C) 100 MHz 
D) 900 MHz 
E) 10,000 MHz

Question 14

The sun is about 1.5 * 1011 m away.The time for light to travel this distance is about:

Accepted Answer

A) 4.5 * 1019 s 
B) 8 s 
C) 8 min 
D) 8 hr 
E) 8 yr 
A) 4.5 * 1019 s 
B) 8 s 
C) 8 min 
D) 8 hr 
E) 8 yr

Question 15

The separation of white light into colors by a prism is associated with:

Accepted Answer

A) total internal reflection 
B) partial reflection from each surface 
C) variation of index of refraction with wavelength 
D) a decrease in the speed of light in the glass 
E) selective absorption of various colors 
A) total internal reflection 
B) partial reflection from each surface 
C) variation of index of refraction with wavelength 
D) a decrease in the speed of light in the glass 
E) selective absorption of various colors

Question 16

If nwater = 1.33 and nglass = 1.50, then total internal reflection at an interface between this glass and water:

Accepted Answer

A) occurs whenever the light goes from glass to water 
B) occurs whenever the light goes from water to glass 
C) may occur when the light goes from glass to water 
D) may occur when the light goes from water to glass 
E) can never occur at this interface 
A) occurs whenever the light goes from glass to water 
B) occurs whenever the light goes from water to glass 
C) may occur when the light goes from glass to water 
D) may occur when the light goes from water to glass 
E) can never occur at this interface

Question 17

An electromagnetic wave is traveling in the positive x direction with its electric field along the z axis and its magnetic field along the y axis.The fields are related by:

Accepted Answer

A) "$\partial$E/$\partial$x = $\mu$0$\varepsilon$0$\partial$B/$\partial$x" 
B) "$\partial$E/  $\partial$ x = $\mu$0$\varepsilon$0$\partial$B/$\partial$t" 
C) "$\partial$B/$\partial$x = $\mu$0$\varepsilon$0$\partial$E/$\partial$x" 
D) "$\partial$B/$\partial$x = $\mu$0$\varepsilon$0$\partial$E/$\partial$t" 
E) "$\partial$B/$\partial$x = -$\mu$0$\varepsilon$0$\partial$E/$\partial$t" 
A) "$\partial$E/$\partial$x = $\mu$0$\varepsilon$0$\partial$B/$\partial$x" 
B) "$\partial$E/  $\partial$ x = $\mu$0$\varepsilon$0$\partial$B/$\partial$t" 
C) "$\partial$B/$\partial$x = $\mu$0$\varepsilon$0$\partial$E/$\partial$x" 
D) "$\partial$B/$\partial$x = $\mu$0$\varepsilon$0$\partial$E/$\partial$t" 
E) "$\partial$B/$\partial$x = -$\mu$0$\varepsilon$0$\partial$E/$\partial$t"

Question 18

A ray of light in water (index n1)is incident on its surface (with air)at the critical angle.Some oil (index n2)is now floated on the water.The angle between the ray in the oil and the normal is:

Accepted Answer

A) sin-1(1.00) 
B) sin-1(1/n1) 
C) sin-1(1/n2) 
D) sin-1(n1/n2) 
E) sin-1(n2/n1) 
A) sin-1(1.00) 
B) sin-1(1/n1) 
C) sin-1(1/n2) 
D) sin-1(n1/n2) 
E) sin-1(n2/n1)

Question 19

The electric field for a plane electromagnetic wave traveling in the +y direction is shown.Consider a point where is in the +z direction.The field is:

Accepted Answer

A) in the +x direction and in phase with the field 
B) in the -x direction and in phase with the field 
C) in the +x direction and 1/4 wave out of phase with the field 
D) in the +z direction and in phase with the field 
E) in the +z direction and 1/4 wave out of phase with the field 
A) in the +x direction and in phase with the field 
B) in the -x direction and in phase with the field 
C) in the +x direction and 1/4 wave out of phase with the field 
D) in the +z direction and in phase with the field 
E) in the +z direction and 1/4 wave out of phase with the field

Question 20

Three polarizing sheets are placed in a stack with the polarizing directions of the first and third perpendicular to each other.Which of the following angles should the polarizing direction of the middle sheet make with the polarizing direction of the first sheet to obtain zero transmitted intensity when unpolarized light is incident on the stack?

Accepted Answer

A) 0° 
B) 30$\degree$ 
C) 45$\degree$ 
D) 60$\degree$ 
E) all angles allow light to pass through 
A) 0° 
B) 30$\degree$ 
C) 45$\degree$ 
D) 60$\degree$ 
E) all angles allow light to pass through

Exam 33: Electromagnetic Waves

A sinusoidal electromagnetic wave has an electric field whose rms value is 100 V/m.What is the instantaneous rate S of energy flow for this wave?

At a certain point and a certain time the electric field of an electromagnetic wave is in the negative z direction and the magnetic field is in the positive y direction.Which of the following statements is true?

If the electric field in a plane electromagnetic wave is along the y axis and its magnitude is given by Em sin (kx + ω \omega ω t)in SI units, then the magnetic field is along the z axis and its magnitude is given by:

A pole stands in a river, half in and half out of the water.Another pole of the same length stands vertically on the shore at a place where the ground is level.The shadow cast by the pole in the river on the river bottom is:

An electromagnetic wave is transporting energy in the negative y direction.At one point and one instant the magnetic field is in the positive x direction.The electric field at that point and instant is:

The electric field in unpolarized light:

The magnetic field in a sinusoidal light wave has an amplitude of 3.3 * 10-7 T.The intensity of the wave is:

The diagram shows total internal reflection.Which of the following statements is NOT true?

A sinusoidal electromagnetic wave with an electric field amplitude of 100 V/m is incident normally on a surface with an area of 1 cm2 and is completely absorbed.The energy absorbed in 10 s is:

Maxwell's equations predict that the speed of electromagnetic waves in free space is given by:

The illustration shows total internal reflection taking place in a piece of glass.The index of refraction of this glass:

The diagram shows the passage of a ray of light from air into a substance X.The index of refraction of X is:

Radio waves of wavelength 3 cm have a frequency of:

The sun is about 1.5 * 1011 m away.The time for light to travel this distance is about:

The separation of white light into colors by a prism is associated with:

If nwater = 1.33 and nglass = 1.50, then total internal reflection at an interface between this glass and water:

An electromagnetic wave is traveling in the positive x direction with its electric field along the z axis and its magnetic field along the y axis.The fields are related by:

A ray of light in water (index n1)is incident on its surface (with air)at the critical angle.Some oil (index n2)is now floated on the water.The angle between the ray in the oil and the normal is:

The electric field for a plane electromagnetic wave traveling in the +y direction is shown.Consider a point where is in the +z direction.The field is:

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If the electric field in a plane electromagnetic wave is along the y axis and its magnitude is given by E_msin (kx + $\omega$ t)in SI units, then the magnetic field is along the z axis and its magnitude is given by:

The magnetic field in a sinusoidal light wave has an amplitude of 3.3 * 10^-7T.The intensity of the wave is:

A sinusoidal electromagnetic wave with an electric field amplitude of 100 V/m is incident normally on a surface with an area of 1 cm² and is completely absorbed.The energy absorbed in 10 s is:

The illustration shows total internal reflection taking place in a piece of glass.The index of refraction of this glass: $The illustration shows total internal reflection taking place in a piece of glass.The index of refraction of this glass:$

The diagram shows the passage of a ray of light from air into a substance X.The index of refraction of X is: $The diagram shows the passage of a ray of light from air into a substance X.The index of refraction of X is:$

The sun is about 1.5 * 10¹¹ m away.The time for light to travel this distance is about:

If n_water = 1.33 and n_glass = 1.50, then total internal reflection at an interface between this glass and water:

A ray of light in water (index n₁)is incident on its surface (with air)at the critical angle.Some oil (index n₂)is now floated on the water.The angle between the ray in the oil and the normal is: