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PHYS126 Spring 2006
Introduction to Modern Physics
Midterm Exam C Set A


Date: 25 March 2006
Time: 9:30-11:30 am

Name: _________________________
Student ID: _____________________
Seat No.: _______

Part
Marks

I (15)


II (25)


III (20)


IV (40+10)


Total marks







Formulae provided:











Part I Multiple Choice Questions (3 pts each, total 15 pts) Circle one answer only.

1) Which are the postulates (basic assumptions) for the special theory of relativity?
Note: All the statements below are true.)
(
A) The speed of light is the same for everyone.
The laws of nature are the same for everyone.

B) For every action there is an equal and opposite reaction.
The concept of simultaneous events must be given up.

C) E = mc2.
The laws of nature are the same for everyone.

D) An object at rest will stay at rest unless acted upon by an external force.
The speed of light is the same for everyone.

E) The laws of nature are the same for everyone.
For every action there is an equal and opposite reaction.

2) As measured by an observer in reference S, two events, A and B, occur at the same position XA = XB . Event A and B occurred at TA and TB respectively, and TB > TA. When these events are observed by a second observer in reference frame S, moving with espect to S, we can be certain that:
r
A) XA > XB B) XA = XB C) XA < XB D) TA > TB
E) TA = TB F) TA < TB G) none of these

) According to general relativity, how is time affected by gravity?
3
A) Time is not affected by gravity.
B) Time is affected by gravity, but not in a predictable way.
C) Time runs faster in stronger gravitational fields.
D) Time runs slower in stronger gravitational fields.
E) Time is stopped by any gravitational field.

4) Using the same crystal, we can see diffraction patterns using either X-ray or electrons. To see the same diffraction angle for the two cases, the X-ray and the electron must ave
h
A) the same wavelength
B) the same wavelength, the same momentum and the same energy
C) the same momentum and the same energy
D) the same energy
E) this is not possible

5) Two stars, A and B (thermal radiators) are at the same distance from us. Emission from A peaks at 600 nm, while emission from B peaks at 300 nm. The energy output from the two are measured to be about the same. The ratio of the diameters between A nd B is (DA/DB):
a
A) 0.5 B) 2 C) 16 D) 8 E) 4 F) 0.25 G) None of these


Part II Experiments (25 pts total)

6) Our modern knowledge of what matters are made of came from experiments. For each of the following, in the space provide