Deck 12: Electromagnetic Waves

Question 1

Find the frequency of X-rays of wavelength 1 Å = 10-10 m.

A)3 * 1018 Hz
B)3 * 1010 MHz
C)6 *109 Hz
D)3 *108 Hz
E)3 * 1020 Hz

Answer 1

3 * 1018 Hz

Question 2

A solar cell has a light-gathering area of 10 cm2 and produces 0.2 A at 0.8 V (DC) when illuminated with S = 1000 W/m2 sunlight.What is the efficiency of the solar cell?

A)16%
B)7%
C)23%
D)4%
E)32%

Answer 2

16%

Question 3

What is the maximum radiation pressure exerted by sunlight in space (S = 1 350 W/m2) on a flat black surface?

A)2.25 * 10-5 Pa
B)0.06 Pa
C)7 * 10-4 Pa
D)4.5 * 10-6 Pa
E)9.0 *10-6 Pa

Answer 3

4.5 * 10-6 Pa

Question 4

At a distance of 10 km from a radio transmitter, the amplitude of the E-field is 0.20 volts/metre.What is the total power emitted by the radio transmitter?

A)10 kW
B)67 kW
C)140 kW
D)245 kW
E)21 kW

Question 5

The Earth is 1.49 * 1011 metres from the Sun.If the solar radiation at the top of the Earth's atmosphere is 1 340 W/m2, what is the total power output of the Sun?

A)7.10*1027 W
B)2.20 * 1030 W
C)6.62 * 1026 W
D)3.74 * 1026 W
E)2.98 * 1025 W

Question 6

If the radiant energy from the Sun comes in as a plane EM wave of intensity 1340 W/m2, calculate the peak values of E and B.

A)300 V/m, 10-4 T
B)1000 V/m, 3.35 * 10-6 T
C)225 V/m, 1.60* 10-3 T
D)111 V/m, 3.00 * 10-5 T
E)711 V/m, 2.37 *10-6 T

Question 7

The magnetic field of a plane-polarised electromagnetic wave moving in the z-direction is given by in SI units.What is the maximum E-field?

A)1000 V/m
B)180 V/m
C)81 V/m
D)360 V/m
E)0.40 V/m

Question 8

What should be the height of a dipole antenna (of dimensions 1/4 wavelength) if it is to transmit 1200 kHz radiowaves?

A)11.4 m
B)60 cm
C)1.12 m
D)62.5 m
E)250 m

Question 9

What is the maximum radiation pressure exerted by sunlight in space (S = 1 350 W/m2) on a highly polished silver surface?

A)1.4 * 10-2 Pa
B)0.12 Pa
C)9.0 * 10-6 Pa
D)4.5 * 10-5 Pa
E)2.3 *10-6 Pa

Question 10

An FM radio station broadcasts at 98.6 MHz.What is the wavelength of the radiowaves?

A)60.8 m
B)6.08 m
C)3.04 m
D)0.314 m
E)0.33 cm

Question 11

How much electromagnetic energy is contained in each cubic metre near the Earth's surface if the intensity of sunlight under clear skies is 1000 W/m2?

A)3.3 * 10-6 J
B)3.3 J
C)0.003 J
D)10-4 J
E)3.0 * 105 J

Question 12

If the maximum E-component of an electromagnetic wave is 600 V/m, what is the maximum B-component?

A)1.4 T
B)1.8 * 10-5 T
C)2.0 * 10-6 T
D)1.0 * 10-3 T
E)1.6 *10-10 T

Question 13

Green light has a wavelength of 5.4 *10-7 m.What is the frequency of this EM-wave in air?

A)5.55*1014 Hz
B)6.00 *1011 Hz
C)9.00 * 108 Hz
D)3.00 *1010 MHz
E)1.80 * 1015 Hz

Question 14

Find the force exerted by reflecting sunlight off a reflecting aluminium sheet in space if the area normal to the sunlight is 10 000 m2 and the solar intensity is 1350 W/m2.

A)0.72 N
B)0.09 N
C)9 N
D)45 N
E)0.18 N

Question 15

What is the average value of the magnitude of the Poynting vector at 1 metre from a 100-watt light bulb radiating in all directions?

A)1 W/m2
B)4 W/m2
C)2 W/m2
D)8 W/m2
E)12 W/m2

Question 16

The magnetic field of a plane-polarised electromagnetic wave moving in the z-direction is given by in SI units.What is the frequency of the wave?

A)500 MHz
B)250 kHz
C)1.25 MHz
D)10 mHz
E)300 MHz

Question 17

The magnetic field of a plane-polarised electromagnetic wave moving in the z-direction is given by in SI units.What is the wavelength of the EM wave?

A)120 m
B)240 m
C)60 m
D)100 m
E)360 m

Question 18

The magnetic field of a plane-polarised electromagnetic wave moving in the z-direction is given by in SI units.Find the average power per square metre carried by the EM wave.

A)720 W
B)172 W
C)500 W
D)2* 107 W
E)86 W

Question 19

The magnetic field of a plane-polarised electromagnetic wave moving in the z-direction is given by in SI units.What is the speed of the EM wave?

A)3 * 108 m/s
B)100 m/s
C)106 m/s
D)2 *107 m/s
E)2 *108 m/s

Question 20

A 100-kW radio station emits EM waves in all directions from an antenna on top of a mountain.What is the intensity of the signal at a distance of 10 km?

A)8 * 10-5 W/m2
B)8 * 10-6 W/m2
C)3 * 10-3 W/m2
D)0.8 W/m2
E)2.5 * 10-5 W/m2

Question 21

In the atmosphere, the shortest wavelength electromagnetic waves are called:

A)microwaves.
B)infrared waves.
C)ultraviolet waves.
D)X-rays.
E)gamma rays.

Question 22

A plane parallel plate capacitor has plates of 10 cm2 area that are 1.0 mm apart.At an instant when charge is being accumulated on the plates at a rate of 12 nC/s, the displacement current between the plates is:

A)1.06 * 10-16 A.
B)1.2 * 10-8 A.
C)8.85 * 10-9 A.
D)1.00 A.
E)1.36 A.

Question 23

A possible means of spaceflight is to place a perfectly reflecting aluminised sheet into Earth orbit and use the light from the Sun to push this solar sail.If a huge sail of area 6.00 *105 m2 and mass 6000 kg were placed into orbit and turned toward the Sun, what would be the force exerted on the sail? (Assume a solar intensity of 1380 W/m2.)

Question 24

Two identical silver spheres of mass m and radius r are placed a distance R (sphere 1) and 2R (sphere 2) from the Sun respectively.The ratio of the gravitational force exerted by the Sun on sphere 1 to the pressure of solar radiation on sphere 1 is T1; the ratio for sphere 2 is T2.The ratio of T2 to T1 is:

A)0.25.
B)0.50.
C)1.0.
D)2.0.
E)4.0.

Question 25

In an electromagnetic wave, 1) how are the electric and magnetic field directions related and 2) how is the direction of travel determined from their directions? ( is the velocity of the light wave.)

A)
B)
C)
D)
E)

Question 26

The magnetic field amplitude in an electromagnetic wave in vacuum is related to the electric field amplitude by B = :

A)
B)
C)E.
D)
E)cE.

Question 27

You can raise the temperature of an object with:

A)microwaves.
B)infrared waves.
C)ultraviolet rays.
D)microwaves, infrared waves and ultraviolet waves.
E)microwaves and infrared rays.

Question 28

High frequency alternating current is passed through a solenoid that contains a solid copper core insulated from the coils of the solenoid.Which statement is correct?

A)A copper core remains cool no matter what the frequency of the current in the solenoid is.
B)The copper core remains cool because the induced emf is parallel to the solenoid axis and fluctuates rapidly.
C)The copper core heats up because an emf parallel to the solenoid axis is induced in the core.
D)The copper core heats up because circular currents around its axis are induced in the core.
E)The copper core heats up because the electric field induced in the copper is parallel to the magnetic field produced by the solenoid.

Question 29

The speed of light is given by the value of:

A)( $\varepsilon$ 0 $\mu$ 0.)
B)
C)
D)
E)

Question 30

Magnetic fields are produced by:

A)constant electric currents.
B)electric currents that vary sinusoidally with time.
C)time-varying electric fields.
D)all of the above.
E)only (a) and (b) above.

Question 31

The intensity of radiation reaching the Earth from the Sun is 1350 W/m2.The Earth's radius is 6.4 *106 m.How big a force does this radiation exert on the Earth? (Assume it is all absorbed.)

A)5.8 * 108 N
B)1.2 *109 N
C)2.3*109 N
D)4.6 *109 N
E)1.7 * 1017 N

Question 32

At every instant the ratio of the magnitude of the electric to the magnetic field in an electromagnetic wave in vacuum is equal to:

A)the speed of radio waves.
B)the speed of light.
C)the speed of gamma rays.
D)all of the above.
E)only (a) and (b) above.

Question 33

When E and B are the amplitudes of the electric and magnetic fields in an electromagnetic wave in vacuum, the total average energy density in the wave is:

A)
B)
C)( $\varepsilon$ 0E2.)
D)
E)

Question 34

A spherical particle of density and 2.00 mm radius is located at the same distance from the Sun as the Earth.RSE = 1.5 *1011 m..If the particle absorbs 100 per cent of the sunlight reaching it, the ratio of the force exerted by the solar radiation to the force of gravity exerted on the particle by the Sun is:

A)5.8 * 10-5.
B)0.58.
C)1.0.
D)1.7.
E)1.7 * 104.

Question 35

Since $\varepsilon$ 0 = 8.85 *10-12 C2 / N . m2, the units of $\varepsilon$ 0E2 can be reduced to:

A)
B)
C)
D)
E)

Question 36

An open circuit consists of a 12 $\mu$ F parallel plate capacitor charged to 200 V and a 10 $\Omega$ resistor.At the instant when a switch closes the circuit (with no battery in it) the displacement current between the plates of the capacitor is:

A)1.2 $\mu$ A.
B)2.4 * 10-4 A.
C)2.4 mA.
D)10 A.
E)20 A.

Question 37

The Sun radiates energy at a rate of 3.86 * 1026 W.Its radius is 7.0 * 108 m.If the distance from the Earth to the Sun is 1.5 * 1011 m, what is the intensity of solar radiation at the top of the Earth's atmosphere?

Question 38

Two identical silver spheres of mass m and radius r are placed a distance R (sphere 1) and 2R (sphere 2) from the Sun respectively.The ratio of the pressure of solar radiation on sphere 2 to that on sphere 1 is:

A)0.25.
B)0.50.
C)1.0.
D)2.0.
E)4.0.

Question 39

Near the surface of the planet, the Earth's magnetic field is about 0.50 * 10-4 T.How much energy is stored in 1.0 m3 of the atmosphere because of this field?

Question 40

The correct form of Ampere's law for circuits with gaps in them is:

A)
B)
C)
D)
E)