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7C
Review Problems for Midterm 2 (Spring 2009)
1)
You have a stack of N polarizers. You rotate them so the total angle between first and
last is 90
°
, and so each adjacent pair is equally spaced. ( for example for N=3, the
first two are 45
°
apart, the next is 45
°
again, for a total of 90
°
between first and last. )
If you send in unpolarized light at intensity I
o
, what intensity comes out? Find
a.
a number for N = 2,3,4;
b.
a formula for general N
c.
the limit as N goes to infinity. Interpret what this limit means physically.
2)
A relativistic snake of proper length 100cm is moving at speed v = 0.6c to the right
across a table. A mischievous grad student, wishing to tease the snake, holds two
hatchets 100cm apart and plans to bounce them simultaneously on the table so that
the left hatchet lands immediately behind the snake’s tail.
The student
argues as
follows:
“The snake is moving with
β
=.6. Therefore its length is contracted by a
factor
γ
= 5/4 and its length (as measured in my frame) is 80cm. This
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 Spring '08
 LIN
 Quantum Physics, Special Relativity, 90°, 20cm, 1G, B. Westbrook, J. Kjall

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