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Check Your Understanding A molecule is vibrating at a frequency of What is the smallest spacing between its vibrational energy levels?
The energy quantum that corresponds to this frequency is
When vibrations have amplitude the energy of oscillations is
Check Your Understanding Would the result in [link] be different if the mass were not 1.0 kg but a tiny mass of 1.0 µ g, and the amplitude of vibrations were 0.10 µ m?
No, because then
When Planck first published his result, the hypothesis of energy quanta was not taken seriously by the physics community because it did not follow from any established physics theory at that time. It was perceived, even by Planck himself, as a useful mathematical trick that led to a good theoretical “fit” to the experimental curve. This perception was changed in 1905 when Einstein published his explanation of the photoelectric effect, in which he gave Planck’s energy quantum a new meaning: that of a particle of light.
Which surface has a higher temperature – the surface of a yellow star or that of a red star?
yellow
Describe what you would see when looking at a body whose temperature is increased from 1000 K to 1,000,000 K.
Explain the color changes in a hot body as its temperature is increased.
goes from red to violet through the rainbow of colors
Speculate as to why UV light causes sunburn, whereas visible light does not.
Two cavity radiators are constructed with walls made of different metals. At the same temperature, how would their radiation spectra differ?
would not differ
Discuss why some bodies appear black, other bodies appear red, and still other bodies appear white.
If everything radiates electromagnetic energy, why can we not see objects at room temperature in a dark room?
human eye does not see IR radiation
How much does the power radiated by a blackbody increase when its temperature (in K) is tripled?
A 200-W heater emits a 1.5-µm radiation. (a) What value of the energy quantum does it emit? (b) Assuming that the specific heat of a 4.0-kg body is how many of these photons must be absorbed by the body to increase its temperature by 2 K? (c) How long does the heating process in (b) take, assuming that all radiation emitted by the heater gets absorbed by the body?
a. 0.81 eV; b. c. 2 min 20 sec
A 900-W microwave generator in an oven generates energy quanta of frequency 2560 MHz. (a) How many energy quanta does it emit per second? (b) How many energy quanta must be absorbed by a pasta dish placed in the radiation cavity to increase its temperature by 45.0 K? Assume that the dish has a mass of 0.5 kg and that its specific heat is (c) Assume that all energy quanta emitted by the generator are absorbed by the pasta dish. How long must we wait until the dish in (b) is ready?
(a) For what temperature is the peak of blackbody radiation spectrum at 400 nm? (b) If the temperature of a blackbody is 800 K, at what wavelength does it radiate the most energy?
a. 7245 K; b. 3.62 μm
The tungsten elements of incandescent light bulbs operate at 3200 K. At what frequency does the filament radiate maximum energy?
Interstellar space is filled with radiation of wavelength This radiation is considered to be a remnant of the “big bang.” What is the corresponding blackbody temperature of this radiation?
about 3 K
The radiant energy from the sun reaches its maximum at a wavelength of about 500.0 nm. What is the approximate temperature of the sun’s surface?
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