=========================preview======================
(PHYS002)solfa_f01.pdf
Back to PHYS002 Login to download
======================================================
Physics 002 Final Examination 15 December, 2001.
Time allowed: 90 minutes Total: 80 marks


A



Data table:
1 parsec
3.26 light years

1 parsec
206,265 AU

1 Astronomical Unit
1.50 1011 m

Speed of light
3 108 m/s

Universal gravitational constant
6.67 10-11 N.m2/kg2

Mass of Sun
1.99 1030 kg

Our distance from the center of Milky Way
8,500 pc




Part A Multiple choice (20 marks):

(1)
Which of the following would not be a piece of evidence in support of the general theory of relativity?

A. The precession of the orbit of Mercury around the Sun.
B. The prolonged decay of high-speed muons from space.
C. The change in the orbital period of a binary system of neutron stars.
D.The image of a distant galaxy appearing as a ring around a massive object.
E. A change in the frequency of light as it travels towards the Earth.
Ans. B



The prolonged decay of high-speed muons from space is due to time dilation, which is an effect of special relativity. The other phenomena are due to general relativity.

(2)
The X-ray pulses from a pulsar change their intensity periodically over 100 days. What is the most probable cause of this periodic variation?

A. Back-and-forth transfer of mass between a red giant and a neutron star.
B. Bursts of carbon explosions.
C. Radiation of gravitational waves by a pair of neutron stars.
D. Synchrotron radiation.
E. The orbital motion of a neutron star in a binary system.


Ans. E

When a neutron star orbits in a binary system, it can be blocked by its companion star. This leads to a change in the intensity of the pulses. It is possible that the orbital period is of the order of 100 days. For example, SS433 has an orbital period of 168 days.

(3)
How does the future of the universe depend on its density?

A. If its density is greater than or equal to the critical density, then the night sky will be darker in the future.
B. If its density is less than the critical density, then the temperature of the cosmic background radiation will eventually rise.
C. If its density is equal to the critical density, then the Hubble constant in the future will be equal to its present value.
D. If scientists find that there is no dark matter in the universe, then the rate of expansion the universe will be faster and faster.
E. None of the above.
Ans. E



If the density is greater than the critical density, the universe will contract eventually. The nights will become brighter.
If the density is less than the critical density, the universe will expand forever. The temperature of the background radiation will continue to drop.
If the density is equal to the critical density, the cosmic expansion will eventually approach zero. The Hubble constant will approach zero, and is less than its present value.
If scientists find that there is no dark matter in the universe, the d