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# hw2answers - Homework Assignment 2 Answers PHYS 206 The...

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Homework Assignment 2 Answers PHYS 206: The Milky Way Inside and Out In the following multiple choice items, there may be one or more correct answers. 1. Galileo Galilei: (a) invented the telescope. (b) was the first to use the telescope for astronomy. (c) observed the phases of Venus, and concluded that it supported the Ptolemaic universe. (d) observed sunspots, and used them to measure the rotational period of the sun. (e) knew about the proposals of Copernicus and Kepler that the earth moved around the sun. 2. Isaac Newton: (a) showed that white light can be split with a prism into exactly two colors, red and blue. (b) proposed a law of gravity, in which the force between two bodies is proportional to the product of their masses, and inversely proportional to the square of the distance between them. (c) studied both light and gravity. (d) constructed the first telescope. 3. Light: (a) comes in two different modes: it can be either a wave, or it can be a particle. (b) has a dual nature: all light can be described as a wave and as a particle. (c) can be characterized by either a wavelength or energy (d) travels at a constant speed in a vacuum, regardless of either the wavelength or frequency. (e) has a higher velocity at higher frequencies. 4. (a) Write down the relationship between the velocity of light and its frequency and wavelength, using the commonly used variable letters. (b) What is the speed of light in a vacuum, in units of cm/sec? (c) If the wavelength of light is 1 cm, what is its frequency? (d) If the frequency of light is 1 s - 1 what is its wavelength? a) c = b) c = 3 × 10 10 cm / sec . c) f = c/λ = (3 × 10 10 cm / sec) / (1cm) = 3 × 10 10 /sec d) λ = c/f = (3 × 10 10 cm / sec) / (1s - 1 ) = 3 × 10 10 cm . 5. Give an approximate wavelength (in meters) for Note: These are approximate wavelengths; there is no hard definition : (a) radio waves. 0.0005-0.3 m (b) infra-red radiation 1 × 10 - 6 30 × 10 - 6 m (c) optical light. 300 × 10 - 9 - - 700 × 10 - 9 m (d) ultra-violet radiation. 20 × 10 - 9 - - 200 × 10 - 9 (e) X-ray radiation 0 . 1 × 10 - 10 - - 100 × 10 - 10 m 6. Which of the following is not electromagnetic radiation: (a) neutrinos (b) gravity waves (c) gamma-rays (d) light from a light bulb. 7. Grouping stars by constellation: (a) permits one to refer to them in discussion, so that they can be talked about. (b) also groups them physically, since stars so close together on the sky are all probably at the same distance. 1

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(c) does not clarify the relationship between the constellations, such as where they are located with respect to one another on the sky. (d) is not generally used by astronomers, since the discovery of new stars would require the arbitrary naming of new constellations.
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hw2answers - Homework Assignment 2 Answers PHYS 206 The...

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