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# Chapter 4 - Chapter 4 Review Question Answers 1 A blackbody...

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Chapter 4 Review Question Answers 1. A blackbody glowing with which of the following colors is hottest? a. yellow, b. red, c. orange, d. violet, e. blue (d) a violet color is the hottest. 2. Of the following photons, which has the lowest energy? a. infrared, b. gamma rays, c. visible light, d. ultraviolet, e. X ray (c) visible light is the lowest energy. 3. The spectrum of which of the following objects will show a blueshift? a. an object moving just eastward on the celestial sphere, b. an object moving just northward on the celestial sphere, c. an object moving directly toward Earth, d. an object moving directly away from Earth, e. an object that is not moving relative to Earth (c) an object moving directly towards the Earth will be blue shifted. 4. What is a blackbody? What does it mean to say that a star appears almost like a blackbody? If stars appear to be like blackbodies, why are they not black? A blackbody is a hypothetical object whose radiated spectrum depends only on its temperature. A star is described as almost like a blackbody when the continuous part of that star’s spectrum follows the shape of a blackbody spectrum. Stars are not black because they are hot and emit large amounts of electromagnetic radiation. They would be black only if they gave off no electromagnetic radiation. 5. What is Wiens law? How could you use it to deter-mine the temperature of a stars surface? Wien’s law is the mathematical relationship between the dominant wavelength and the temperature of a blackbody. It says that the hotter an object is, the shorter the wavelength of the peak of its blackbody curve. This peak is the wavelength that the body emits most intensely. Since all blackbodies with the same temperature have the same black body curves, finding the wavelength at the peak of the continuous spectrum enables you to directly calculate the object’s surface temperature. 6. What is the Stefan- Boltzmann law? How do astronomers use it? The Stefan-Boltzmann law is

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Chapter 4 - Chapter 4 Review Question Answers 1 A blackbody...

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