Through which of the following materials does light travel fastest?
Definition
vacuum
Term
What was the very first observation that showed conclusively that light travels at a finite speed (not infinitely fast)?
Definition
Eclipses of Jupiter's moons, when they moved into or out of Jupiter's shadow, appeared to occur later than they should when Jupiter was farther away from Earth
Term
Approximately how many times around Earth (at the equator) could a beam of light travel in one second?
Definition
about 7½
Term
How long does it take light to travel from the Sun to Earth, a distance of 1.50 [image] 108 km?
Definition
8 1/3 minutes
Term
Historically, the wave nature of light was first demonstrated by
Definition
the interference produced when light passes through a double slit.
Term
Your cellular phone is actually a radio transmitter and receiver. You receive an incoming call in the form of a radio wave of frequency 880.65 MHz. What is the wavelength (in meters) of this wave?
Definition
2.61 [image] 1014 Hz
Term
The energy emitted per second by the Sun is greatest at a wavelength of about 500 nm. The energy emitted per second by a star having half the temperature of the Sun would be greatest at a wavelength of about
Definition
1000 nm in the infrared.
Term
Using Wien's law and the Stefan-Boltzmann law, explain the color and intensity changes that are observed as the temperature of a hot, glowing object increases.
Definition
As the temperature of a hot, glowing object increases it will be seen to glow more brightly. This is described by the Stephan-Boltzmann law, which shows the emitted flux of radiation increasing with the fourth power of the temperature. The color of the glowing object will be seen to shift toward the short-wavelength end of the spectrum in accord with Wien's law, which shows the peak wavelength in the spectrum decreasing as the temperature increases.
Term
One blackbody is at 6000 K and a second blackbody is at 3000 K. How many times more energy is radiated by the hotter object than the cooler one?
Definition
16
Term
There are no green stars because
Definition
as a star increases in temperature, the visible spectrum it produces changes from red to red plus green to red plus green plus blue, and none of these combinations looks green
Term
The bright star Bellatrix in the constellation Orion has a surface temperature of 21,500 K. What is its wavelength of maximum emission in nanometers? What is the color of the star?
Definition
135. blue.
Term
One beam of pure light has a high frequency and a short wavelength, while a second pure beam has a low frequency and a long wavelength. A photon from the high-frequency beam has ___________ than a photon from the low-frequency beam.
Definition
more energy
Term
The important breakthrough in theoretical physics that was first suggested by Planck to explain the shape of the spectrum of a hot body was the
Definition
concept that electromagnetic energy was emitted in small packets or quanta.
Term
The first person to show that light traveled in wave packets, or photons, in which the energy of a photon depends on its wavelength, was
Definition
Albert Einstein
Term
An atom of singly ionized magnesium has 12 protons in its nucleus. How many electrons surround this nucleus?
Definition
11
Term
Two isotopes of an element differ from one another because
Definition
they have the same number of protons but different numbers of neutrons in their nuclei.
Term
Gold has the atomic number 79, and the stable isotope of gold has the symbol 197Au. How many protons and neutrons does this nucleus have?
Definition
79 protons and 118 neutrons
Term
The physical structure of an atom is
Definition
10–10 m, or 0.1 nm.
Term
According to the Bohr theory, light emitted by atoms originates from
Definition
transitions of electrons between different energy levels in the atom.
Term
When an electron in an atom makes a transition from a higher to a lower orbit, light is
Definition
created, causing a continuous spectrum.
Term
The specific colors of light emitted by an atom in a hot, thin gas (e.g., in a tube in a laboratory or a gas cloud in space) are caused by
Definition
electrons jumping to lower energy levels, losing energy as they do so.
Term
A hydrogen atom in a low-density, hot gas gives off what type of spectrum?
Definition
a series of emission lines spaced in a mathematical sequence
Term
A source of waves emitting waves of a constant frequency approaches you, passes you, and recedes into the distance—all at a constant speed. The frequency of the waves you observe from this source
Definition
is higher (and constant) as the source approaches you and suddenly becomes lower (and constant) as the source moves away from you.
Term
In the spectrum of a particular star, the wavelength of the Hα spectral absorption line of hydrogen is measured to be 656.6 nm, whereas in the laboratory spectrum it is at 656.3 nm. What can you say about this star?
Definition
The star is moving away from the Earth at a speed of 137 km/s.
Term
What is the Doppler effect?
Definition
The Doppler effect is a shift in the observed wavelength due to relative radial motion between the source of the waves and the observer.
Term
Why is the Doppler effect important to astronomers?
Definition
The Doppler effect allows a determination of the relative radial velocity of a source of radiation from an examination of its spectrum
