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Physics 002 Final Examination 20 December, 2003.
Time allowed: 90 minutes Total: 70 marks
Name:
Student ID:
A
Data table:
1 parsec (pc)
3.26 light years
1 parsec (pc)
206,265 AU
Speed of light
3 108 m/s
Universal gravitational constant
6.67 10-11 N.m2/kg2
1 Astronomical Unit
1.50 1011 m
Mass of Sun
1.99 1030 kg
1 rad
206,265 arc sec
Part A Multiple choice (20 marks):
(1) What is the end state of a medium size main sequence star like our sun?
A.
Brown dwarf.
B.
White dwarf.
C.
Neutron star.
D.
Black dwarf.
E.
Black hole. Answer:__D______
(2) Pulsars are believed to slow down because
A.
they are converting energy of rotation into radiation.
B.
there are internal disturbances similar to earthquakes.
C.
there is friction with the interstellar medium.
D.
angular momentum must be conserved.
E.
their mass is decreasing. Answer:___A_____
(3) Where would a supernova explosion most likely occur?
I.
in an elliptical galaxy
II.
in the disk of a spiral galaxy
III.
in the halo of a spiral galaxy
A.
I only
B.
II only
C.
III only
D.
II & III
E.
! & III Answer:___B_____
(4) In Special Relativity,
A.
the speed of light is the same in all media.
B.
nothing can move with a speed faster than the speed of light in water.
C.
time is dilated in any frame.
D.
mass of an object remains the same independent of its speed.
E.
there is no absolute time. Answer:___E_____
(5) Which of the following would be true if our universe is open?
A.
Two parallel light beams would meet at a point in the future.
B.
A Big Crunch would occur in the future.
C.
The density of the Milky Way would be less than the critical density.
D.
The expansion of the universe would accelerate.
E.
The expansion of the universe would never stop. Answer:___E_____
Part B True and False (16 marks):
(1-8) Read carefully the following italicized paragraphs abridged from Scientific American. The theme is about the age of the universe.
Hubble and other pioneers estimated distances to various galaxies by assuming that the ones that appeared bright were comparatively close, and the ones that appeared dim were far away. But this methodology works only crudely, because galaxies differ in their properties. And it fails entirely for distant sources C whose light takes so long to reach the Earth that it reveals the faraway galaxies as they were billions of years ago (that is, in their youth) C because their intrinsic luminosity could have been quite different from that of more mature galaxies seen close to home.
Around the 1970s, astronomers began exploring the idea of using supernovae as standard candl