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Physics 002 Midterm 2 23 April, 2002.
Time allowed: 70 minutes Total: 70 marks

Name:

Student ID:
A




Table 1: Useful Data

1 AU
1.5 108 km

Suns temperature
5,800 K

Suns absolute magnitude
+4.8

Suns lifetime
10 billion y

H line
656.3 nm




Table 2: Spectral Types and Temperatures of Stars

Spectral type
O5
B0
B5
A0
A5
F0
F5

Temperature (K)
40,000
28,000
15,000
9,900
8,500
7,400
6,600




Spectral type
G0
G5
K0
K5
M0
M5
M8

Temperature (K)
6,000
5,500
4,900
4,100
3,500
2,800
2,400




Part A Short Questions (1 mark each):

(1-5) A star of spectral type K0 and luminosity class II has an apparent magnitude of +17. Use Figure 1 to find, to 2 significant figures,
(1)
absolute magnitude of the star





(2)
luminosity of the star (in units of solar luminosity)





(3)
distance of the star from Earth (in pc)





(4)
temperature of the star





(5)
radius of the star (in units of solar radius)








(6-9) Due to the dust in the interstellar medium, a star will appear to an observer on Earth to be

Yes
No

(6)
pinker than it really is, since hydrogen appears pink.






(7)
bluer than it really is, because of scattering.






(8)
cooler than it really is.






(9)
fainter than it really is.









(10-13) Which are true about heat convection in main sequence stars?

Yes
No

(10)
It is not present in upper main sequence stars.






(11)
It prevents the accumulation of helium ash in the core of lower main sequence stars.






(12)
It prevents photons from escaping from the star.






(13)
It is caused by the ionization of hydrogen atoms.









(14-18) Which statements are true about star formation?

Yes
No

(14)
Star formation can be triggered by shock waves generated by supernova explosions.






(15)
Young stars are poorer in heavy elements because heavy elements are formed only at the later stages of stellar evolution.






(16)
Star formation can be triggered by shock waves experienced by interstellar clouds travelling through galactic arms.






(17)
Young stars are richer in heavy elements because they are made from interstellar clouds which are recycled from supernova explosions.






(18)
Star formation can be triggered by shock waves inside globular clusters due to their high density of stars.










Part B Multiple choice (4 marks each):

(1) The radius of a white dwarf decreases with its mass because
A.
inward gravitational force increases with mass.


B.
the pressure-temperature thermostat operates a