Physics 1320 Chapter 26 (Exam 2) – Flashcards
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Most of the waves in the electromagnetic spectrum are
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invisible
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Electromagnetic waves consist of
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oscillating electric and magnetic fields
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The source of all electromagnetic waves is
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accelerating electric charges.
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A changing electric field induces a changing
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magnetic field.
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If a light signal and a radio signal were emitted simultaneously from Alpha Centauri, the first to reach Earth would be the
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both the same time
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If the Sun were to disappear at this moment, we wouldn't know about it for
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8 minutes.
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Which of the following is fundamentally different from the others?
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sound waves
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Which travels with the greatest speed in a vacuum?
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gamma rays, X-rays, light waves AND radio waves all have the same speed
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Which of these electromagnetic waves have the shortest wavelength?
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X-rays
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Which of these electromagnetic waves have the longest wavelength?
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radio waves
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Compared to ultraviolet waves, the wavelength of infrared waves is
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longer
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Compared to ultraviolet waves, the frequency of infrared waves is
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lower
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Compared to radio waves, the velocity of visible light waves in a vacuum is
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the same
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A main difference between a radio wave and a light wave is
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frequency AND wavelength.
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If the color spectrum ranges from red to violet, then it ranges from
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Both long wavelengths to short wavelengths and low frequencies to high frequencies.
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What is the wavelength of a 1-hertz electromagnetic wave?
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more than 1 m
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What is the wavelength of an electromagnetic wave that has a frequency of 3 kilohertz?
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more than 1 km
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What is the frequency of an electromagnetic wave that has a wavelength of 300,000 km?
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1 Hz
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A main difference between a radio wave and a sound wave is
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medium or no medium.
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Sunburns are produced by
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ultraviolet light.
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Which best shields you from sunburn when at the beach?
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a sheet of glass between you and the Sun
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Kids in elementary school get this right: Which color of light gets through red glass?
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red
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The fact that you can see stars in the nighttime sky is evidence that
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our atmosphere is transparent to visible light AND light can travel in a vacuum.
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Which of the following cannot travel in a vacuum?
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a sound wave
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If an electric charge is shaken up and down frequently enough
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light can be emitted.
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If an electron vibrates up and down 1000 times each second, it generates an electromagnetic wave having a
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frequency of 1000 Hz.
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The natural frequency of the atoms in glass is in the
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ultraviolet part of the spectrum.
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When visible light is incident upon clear glass, atoms in the glass
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are forced into vibration.
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The speed of light in the void between molecules in glass is
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the same as its speed in a vacuum.
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Compared to its average speed in air, the average speed of a beam of light in glass is
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less.
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Glass is transparent to
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visible light.
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When ultraviolet light is incident upon glass, atoms in the glass
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resonate
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Consider light energy that is momentarily absorbed in glass and then re-emitted. Compared to the absorbed light, the frequency of the re-emitted light is
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the same.
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Glass is transparent to wave frequencies that
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are below its natural frequencies.
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Infrared waves are often called heat waves because they
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induce resonance in molecules and increase internal energy in a substance.
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Metals are shiny because
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their electrons vibrate to the oscillations of any incident light.
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Materials generally become warmer when light is
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absorbed by them.
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Earth's atmosphere is opaque to waves that are concentrated in the
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infrared part of the spectrum.
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A pair of sunglasses and a pair of clear reading glasses are left in the sunlight. The hotter glasses will be the
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sunglasses
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A total shadow is called
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an umbra, and a partial shadow a penumbra.
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A lunar eclipse occurs when the
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Moon passes into Earth's shadow.
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A solar eclipse occurs when the
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the Moon's shadow is cast on Earth.
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A total solar eclipse occurs for people in the Sun's
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umbra
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A partial solar eclipse occurs for people in the Sun's
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penumbra
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While Earth is experiencing a total solar eclipse, an observer on the side of the Moon facing Earth would see
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a dark area moving across the face of Earth.
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An annular eclipse of the Sun occurs when the Moon doesn't quite cover the Sun in the zone of totality. This means that the Moon is
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farther than usual from Earth.
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The round spots of light on the ground beneath a tree on a sunny day are images of
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the Sun.
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The Moon would be at its fullest just before the time of a
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lunar eclipse.
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A new Moon appears in the sky just before the time of a
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solar eclipse.
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When an astronaut on the Moon experiences a solar eclipse, observers on Earth see
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a lunar eclipse.
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The sensation of color is seen when light falls on the eye's
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cones
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The cones in the retina of the eye are
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most densely packed at the center of vision.
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Red-hot and blue-hot stars appear white to the eye because
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they are too dim to fire the cones.
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In the periphery of our vision, we are
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sensitive to movement, but cannot see color.
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Information-carrying nerves are connected to the retina at the
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blind spot.
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The size of the pupil of your eye depends on
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the brightness of light in the room AND your mood.
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The main difference between the retina of a human eye and that of a dog's eye is the
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absence of cones in a dog's retina.
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Colors are barely seen or not at all in nighttime because moonlight
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is too dim to activate the retina's cones.
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In 1887, Albert A. Michelson sent a beam of light from a revolving mirror to a stationary mirror 15 km away. Find the time interval between light leaving and returning to the revolving mirror.
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t = 1.0×10^−4 s
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Find the time for a pulse of laser light to reach the Moon and to bounce back to Earth.
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t = 2.6 s
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The nearest star beyond the Sun is Alpha Centauri, 4.2×1016m away. If we were to receive a radio message from this star today, find the time when it would have been sent.
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t = 4.4 years ago
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A certain radar installation tracks airplanes by transmitting electromagnetic radiation of wavelength 2.6 cm . Find the frequency of this radiation. Find the time required for a pulse of radar waves to reach an airplane 6.0
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12 GHz t = 4.0×10^−5 s
