Download 109 HW#18

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PHY109 Reading Quiz#18
No reading quiz on 3/17(M), but FYI here are typical questions for the sections
assigned.
Answers in bold
1.
In an electromagnetic wave, _________________ in time.
(a) only the electric filed oscillates
(b) only the magnetic filed oscillates
(c) both the electric and magnetic fields oscillate
2. An electromagnetic wave is a _________ wave.
(a) longitudinal
(b) transverse
3. An electromagnetic wave can travel through _________ .
(a) a vacuum only
(b) material substances only
(c) a vacuum and a material substance
4. Both AM and FM radio waves are _________ waves.
(a) sound
(b) electromagnetic
(c) supersonic
5. Radio waves, infrared radiation, visible light, ultraviolet radiation, x-rays, and gamma
rays travel through a vacuum _________ .
(a) at different speeds
(b) at the same speed
6. Radio waves, infrared radiation, visible light, ultraviolet radiation, x-rays, and gamma
rays have _________ .
(a) the same frequency
(b) different frequencies
Reading assignment for 3/19/14 (no reading quiz on this assignment)
1. Sec.24.3
How did Foucault and Michelson measure the speed of light? Read Conceptual Example 3.
How are the permittivity of free space and the permeability of free space related with
the speed of light?
2. Sec.24.4
How does a microwave oven work?
What is the total energy density of an electromagnetic wave in a vacuum?
Which field carries more energy in an electromagnetic wave, the electric field or
the magnetic field?
How is the electric field strength related with the magnetic field strength in
an electromagnetic wave?
How can we find the average energy density of an electromagnetic wave from
the rms values for the electric and magnetic fields?
Read Example 4.
How can we find the intensity of an electromagnetic wave?
Read Example 5.
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2. Sec.24.6 (p.746-747 and p.750-751)
What does “linearly polarized” mean?
How can we generate a polarized electromagnetic wave?
Is the light from an incandescent light bulb polarized?
What is the intensity of the polarized light that is transmitted through a polarizing
material compared to the intensity of the incident unpolarized light?
How do Polaroid sunglasses work?
Homework (Ch.24) due at 1 p.m. on 3/26/14 (W)
1. Which one of the following statements concerning electromagnetic waves is false?
(a) Electromagnetic waves are transverse waves.
(b) Electromagnetic waves carry energy through space.
(c) The existence of electromagnetic waves was predicted by Maxwell.
(d) Electromagnetic waves cannot propagate in a material substance.
(e) Electromagnetic waves can propagate in a vacuum.
2. Which one of the following will not generate electromagnetic waves or pulses?
(a) a steady direct current
(b) an accelerating electron
(c) a proton in simple harmonic motion
(d) an alternating current
(e) charged particles traveling in a circular path in a mass spectrometer
3.
Which one of the following statements concerning electromagnetic waves is false?
(a) Electromagnetic waves carry energy.
(b) X-rays have shorter wavelengths than radio waves.
(c) In vacuum, electromagnetic waves with different wavelengths travel at different speeds.
(d) Lower frequency electromagnetic waves can be produced by oscillating circuits.
(e) They consist of mutually perpendicular electric and magnetic fields that oscillate
perpendicular to the direction of propagation.
4.
The various colors of visible light differ in ____________ .
(a) frequency only (b) wavelength only
(d) frequency and wavelength
5.
6.
(c) their speeds in a vacuum
(e) frequency and their speeds in a vacuum
Which one of the following colors of visible light has the lowest frequency?
(a) yellow
(b) red
(c) green
(d) blue
(e) violet
When a radio telescope observes a region of space between two stars, it detects
electromagnetic radiation that has a wavelength of roughly 0.2 m. This radiation was
emitted by hydrogen atoms in the gas and dust located in that region. What is the frequency
of this radiation?
7
(a) 1.5 × 10 Hz
8
9
10
(b) 1.5 × 10 Hz (c) 1.5 × 10 Hz (d) 1.5 × 10 Hz
11
(e) 1.5 × 10 Hz
3
7.
A radio wave sent from the earth’s surface reflects from the surface of the moon and
returns to the earth. The elapsed time between the generation of the wave and the
detection of the reflected wave is 2.6 s. Find the distance from the surface of the
earth to the surface of the moon.
(a) 390 km
8.
(b) 3900 km
(c) 39000 km
(d) 390000 km
(e) 3900000 km
Which one of the following statements concerning the energy carried by an
electromagnetic wave is true?
(a) The energy is carried only by the electric field.
(b) More energy is carried by the electric field than by the magnetic field.
(c) More energy is carried by the magnetic field than the electric field.
(d) The energy is carried only by the magnetic field.
(e) The energy is carried equally by the electric and magnetic fields.
9.
An electromagnetic wave has an electric field with peak value 20 N/C. What is the
average intensity of the wave? Use ε 0 ≈ 9 × 10−1 2 C 2 / (N ⋅ m 2 ) .
(a) 0.1 W / m2
(b) 0.3 W / m 2
(c) 0.5 W / m 2
(d) 0.7 W / m 2
(e) 0.9 W / m 2