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Physics 002 Midterm 1 10 October 2002.
Time allowed: 70 minutes Total: 70 marks

Name:

Student ID:
A




Part A: True or false questions (18 marks, 2 marks each)



True
False

1
You are located 23.5 degrees South latitude. On 21 September, nights begin to get longer than days.

False

2
If the local time is 3 pm, and the Moon is directly overhead, the most likely phase of the Moon is gibbous.

False

3
During a total lunar eclipse, the Moon is in Earths umbra.
True


4
As viewed from Earth, Venus can go through a full set of phases.
True


5
If you live on Mars, Mercury is never seen in the sky at midnight.
True


6
On a mountain top, a telescope with a diameter of 5 cm is able to distinguish 2 stars separated by an angle of 1 arc seconds.

False

7
Light from stars has an emission spectrum.

False

8
Refracting telescopes suffer from the problems of chromatic aberration and the sagging of mirrors.
True
False

9
Ultraviolet radiation from stars can be detected by Earthbound telescopes.

False




Explanation:
1: 21 September is the Autumnal Equinox. It is Autumn in the Northern Hemisphere, and Spring in the Southern Hemisphere. Days begin to get longer than nights.
2. The Moon has a crescent phase. As seen from above the North Pole,

Sunlight

East horizon


4. As viewed from the Earth, Venus is an inner planet. Hence Venus can go through a set of phases from crescent, quarter, gibbous to nearly full.
5. If you live on Mars, Mercury is an inner planet. Hence it is always seen near the Sun, and can never be seen in the sky at midnight.
6. The resolving angle of the telescope is 11.6/5 = 2.3 arc seconds. Hence the 2 stars separated by an angle of 1 arc second are too near to be distinguished.
7. Light originating from the bodies of stars is a continuous spectrum like blackbody radiation. When it passes through the hot thin gases on the surface of stars, it will create an absorption spectrum.
8. The answer is true. Some students answer false because they point out that the phrase sagging of mirrors should be sagging of lenses, so false is also accepted.


Part B Short questions (16 marks, 2 marks each)

What are the temperatures of the following stars? Give your answer to the nearest thousand degrees Kelvin. (Surface temperature of the Sun = 6,000 K)


Answer

1
A star with a maximum intensity at a wavelength of 800 nm.
4,000 K

2
A star with strong lines of hydrogen.
10,000 K

3
A star whose flux is 25 times that from the Sun.
13,000 K




Explanation:
1. Using Wiens law, the temperature of the star is 3,000,000/800 = 3,750 K 4,000 K.
3.Since Flux Temperature4,




T = 2.236TO = 2.236 6,000 = 13,416 K 13,000 K.













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