PHYS1010 Questions and Answers 100%
Correct
21. Why does the Sun look reddish at sunrise and sunset? High- frequency light (the blue
end of the spectrum) is scattered most. So, at sunrise and sunset, when light follows a long path
through air to reach you, most of the sunlight reaching you is what is left, low-frequency light
(reds, oranges).
23. What is absorbed by water to give it a cyan color? Infrared and red light are absorbed
by water. Absorption of red produces the complementary color, cyan.
25. What prevents rainbows from being seen as complete circles? The ground gets in the
way of viewing a whole circular rainbow.
27. Is polarization a property of transverse waves, longitudinal waves, or both?
Polarization is a property of transverse waves, never longitudinal waves.
29. Will light pass through a pair of Polaroid filters when their axes are aligned? When their axes
are at right angles to each other? Light will pass through the pair when their axes are
aligned, but not when the axes are at right angles to each other.
,39. Consider a pulse of laser light that is aimed at the Moon and bounces back to Earth. The
distance between Earth and the Moon is 3.84 × 108 m. Show that the round-trip time for this
pulse of light is 2.56 s. Earth-Moon distance is 3.84 × 108 m, so the round-trip distance is
7.68 × 108 m. Rearranging .
41. Blue-green light has a frequency of about 6 × 1014 Hz. Using the relationship , show that its
wavelength in air is 5 × 10−7 m. How much larger is this wavelength compared to the size of an
atom, which is about 10−10 m? From , or 500 nanometers. This is 5000 times larger than
the size of an atom, which is about 0.1 nanometer. (The nanometer is a common unit of length in
atomic and optical physics.)
43. When you walk toward a mirror, you see your image approaching you. If you walk at 2 m/s,
how fast do you and your image approach each other? The relative speed of you and your
image toward each other is 4 m/s. (This question could have been asked back in Chapter 1,
"Motion is Relative.")
49. What is the fundamental source of electromagnetic radiation? The fundamental source
of electromagnetic radiation is vibrating electric charges, which emit vibrating electric and
magnetic fields.
, 51. Which has the longest wavelength light waves, X-rays, or radio waves?: The
wavelengths of radio waves are longer than those of light waves, which are longer than the
wavelengths of X-rays.
53. What is the speed of X-rays in a vacuum? X-ray speed is c, the speed of light.
55. What do radio waves and light have in common? What is different about them? Radio
waves and light are both electromagnetic, transverse, move at the speed of light, and are created
and absorbed by oscillating charge. They differ in their frequency and wavelength and in the type
of oscillating charge that creates and absorbs them.
57. Is glass transparent or opaque to light of frequencies that match its own natural frequencies?
Explain. Glass is opaque to frequencies of light that match its own natural frequencies.
This is because the electrons in the absorbing medium are driven to oscillations of much larger
amplitudes than occur for non-resonant frequencies. These large amplitudes result in energy
transfer to neighboring atoms and an increase in thermal energy rather than a re-emission of
light.
59. What determines whether a material is transparent or opaque? Transparency or
opaqueness is determined by the match between incident light frequencies and the resonant
Correct
21. Why does the Sun look reddish at sunrise and sunset? High- frequency light (the blue
end of the spectrum) is scattered most. So, at sunrise and sunset, when light follows a long path
through air to reach you, most of the sunlight reaching you is what is left, low-frequency light
(reds, oranges).
23. What is absorbed by water to give it a cyan color? Infrared and red light are absorbed
by water. Absorption of red produces the complementary color, cyan.
25. What prevents rainbows from being seen as complete circles? The ground gets in the
way of viewing a whole circular rainbow.
27. Is polarization a property of transverse waves, longitudinal waves, or both?
Polarization is a property of transverse waves, never longitudinal waves.
29. Will light pass through a pair of Polaroid filters when their axes are aligned? When their axes
are at right angles to each other? Light will pass through the pair when their axes are
aligned, but not when the axes are at right angles to each other.
,39. Consider a pulse of laser light that is aimed at the Moon and bounces back to Earth. The
distance between Earth and the Moon is 3.84 × 108 m. Show that the round-trip time for this
pulse of light is 2.56 s. Earth-Moon distance is 3.84 × 108 m, so the round-trip distance is
7.68 × 108 m. Rearranging .
41. Blue-green light has a frequency of about 6 × 1014 Hz. Using the relationship , show that its
wavelength in air is 5 × 10−7 m. How much larger is this wavelength compared to the size of an
atom, which is about 10−10 m? From , or 500 nanometers. This is 5000 times larger than
the size of an atom, which is about 0.1 nanometer. (The nanometer is a common unit of length in
atomic and optical physics.)
43. When you walk toward a mirror, you see your image approaching you. If you walk at 2 m/s,
how fast do you and your image approach each other? The relative speed of you and your
image toward each other is 4 m/s. (This question could have been asked back in Chapter 1,
"Motion is Relative.")
49. What is the fundamental source of electromagnetic radiation? The fundamental source
of electromagnetic radiation is vibrating electric charges, which emit vibrating electric and
magnetic fields.
, 51. Which has the longest wavelength light waves, X-rays, or radio waves?: The
wavelengths of radio waves are longer than those of light waves, which are longer than the
wavelengths of X-rays.
53. What is the speed of X-rays in a vacuum? X-ray speed is c, the speed of light.
55. What do radio waves and light have in common? What is different about them? Radio
waves and light are both electromagnetic, transverse, move at the speed of light, and are created
and absorbed by oscillating charge. They differ in their frequency and wavelength and in the type
of oscillating charge that creates and absorbs them.
57. Is glass transparent or opaque to light of frequencies that match its own natural frequencies?
Explain. Glass is opaque to frequencies of light that match its own natural frequencies.
This is because the electrons in the absorbing medium are driven to oscillations of much larger
amplitudes than occur for non-resonant frequencies. These large amplitudes result in energy
transfer to neighboring atoms and an increase in thermal energy rather than a re-emission of
light.
59. What determines whether a material is transparent or opaque? Transparency or
opaqueness is determined by the match between incident light frequencies and the resonant
