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midterm 3 solutions pt. 4

# midterm 3 solutions pt. 4 - ASTR 100 Midterm 3 Version 4...

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ASTR 100 Midterm 3 Version 4 Solutions April 19, 2006 Multiple Choice, 2 pts each. 1. D 6. C 11. A 16. B 21. B 2. B 7. D 12. C 17. B 22. B 3. B 8. B 13. A 18. D 23. B 4. A 9. B 14. C 19. B 24. C 5. D 10. D 15. D 20. D 25. A Short Answer, 10 pts each. 1. Suppose a star formed with half of the mass of the Sun. Describe two things about the star that would be different from the Sun, and explain why. Many things would be different about this star. You needed to name two, and be specific about what the changes would be. For example, saying that the star’s surface temperature would be different is not sufficient: you need to say if it would be hotter or colder and explain why. The star would be smaller in radius. This is because it is made of less material. The star would have a lower surface temperature. This is because its lower mass would less effectively weigh down on the core of the star, causing lower temperatures in the core, leading to a slower rate of fusion. The smaller amount of energy traveling outward through the star would cause its surface temperature to be lower. The star would have a lower luminosity. As in previous item, the star would have a slower rate of fusion, so less energy would be escaping from the star every second, leading to lower luminosity. The star would have a redder color. This is because it has a lower surface temperature. Objects that emit a thermal radiation spectrum emit most of their light at a wavelength determined by their temperature: the higher the temperature, the shorter the wavelength. The star would be in a different spectral class, specifically one corresponding to a lower surface temperature.

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