Problem sets         Physics 9HC      spring 2003
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The latest is listed first!
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You are encouraged to discuss the problems with me, your TA,
or your classmates. However, the solutions that you hand in
must be written by you alone and must be *your own
understanding* of the problem. You may achieve that
understanding on your own or by talking and working with
others, but what goes on the paper you turn in must include
only the understanding that you have reached and not what
someone else has told you is correct. Including on your
paper information that you got from others but do not
understand yourself is a violation of the Code of Academic
Conduct.

You should *not* expect to read a problem and immediately
see how to do it. Expect to spend some time thinking and
trying various approaches until you find one that works. It
usually helps a lot to begin by identifying the fundamental
physical principles involved in the problem.

To get credit for your answers, you must show your work, and
it is to your advantage to make it neat, clear, and
organized. Please keep in mind that you are writing your
solutions for someone else to read---someone who is not a
mind reader and who has limited time to try to figure out
your solution. If we cannot figure out what you have done,
we cannot give you any credit. Write up your solution after
you have figured out how to do it on scratch paper. Whenever
possible, draw a picture and label it with the relevant
physical variables. List the quantities that you are given
with their values and the unknown quantities that you are
trying to find. Then state the most important physical laws
or principles that you are going to use to solve the
problem. If you turn in solutions on problem sets that are
difficult to read and that do not follow this structure, you
will lose points even if your answer is correct!

Usually one or two of the problems will be graded. You will
receive points for turning in solutions to all the problems,
points for the correctness of the problem or problems
that are graded, and points for presentation.

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Problem set 8  due 9am Tuesday, 3 June 
in the locked boxes at the back of our lecture, 55 Ro.

Q8:  S.2 S.6 S.7ab S.8
Q11:  B.1 B.5 S.2

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Problem set 7  due 9am Tuesday, 27 May 
in the locked boxes at the back of our lecture, 55 Ro.

"Additional problem for P. Set 7" on website

Q7: B.3 S.9 R.1
 
Consider a potential step 10eV high so that V(x)=0 for
for x<0 and V(x) = 10eV for x>0.

1. Electrons with a kinetic energy of 15eV are beamed at 
the step from the left. 
  a) Use the Schroedinger to get the momentum of the electrons
     for x>0. How does your result compare with what you would
     get from classical reasoning?
  b) What fraction of the electrons travel to right past the 
     step?

2. Electrons with a kinetic energy of 5eV are beamed at 
the step from the left. Roughly what is the distance to the 
right of x=0 that there is a reasonably large probability to 
observe an electron? 

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Problem set 6  due 9am Tuesday, 20 May 
in the locked boxes at the back of our lecture, 55 Ro.

Do both the probblems called 
"Problem set 6a" and 
"Problem set 6b" on our website. 
In the documents themselves, they are called 
Problem set 6 and Problem set 7

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***Note due Thursday not Tuesday***

Problem set 5  due 9am Thursday, 8 May 
in the locked boxes at the back of our lecture, 55 Ro.

See "Problem set 5" on our website.

This problem set is short. I suggest you think of it as
part of your preparation for the Thursday midterm. 

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Problem set 4  due 9am Tuesday, 29 April 
in the locked boxes at the back of our lecture, 55 Ro.

Q3: S.2 R.1 A.1
Q4: B.3 S.5 S.7 S.11
Q5: B.7

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Problem set 3  due 9am Tuesday, 22 April 
in the locked boxes at the back of our lecture, 55 Ro.

Q2: B.13 S.6 R.3

1. Use the rainbow reflection off the bottom side of a CD to 
estimate the spacing of the "grooves".

2. The claim has been made that spy satellites have gotten so 
good that they can read license plate numbers. Is this claim 
plausible? dubious? ridiculous?

3. Full width at half maximim (FWHM): This is a measure of the width of
a peak. Start at the top and go out to the left until the height is half
the peak height. Let that angle be theta_1. Next do the same thing going
to the right to get theta_2. FWHM is theta_2  - theta_1. For a single
slit diffraction pattern, what is FWHM? Express it in terms of the slit
width and the wavelength. Note: you will need to use your calculator or
computer do make a numerical estimate to the solution of an equation
that you cannot solve analytically.

4. A police car has a siren and a light on the roof. 
On day with no wind when the speed of sound is 300m/s, you 
are standing still, and the police car goes by at 30m/sÑfirst 
approaching then receding. Let the fractional change in 
the frequency be the difference between the approaching 
and receding frequencies divided by the true frequency. 
Compare the fractional change in the frequency of the sound 
and the light. Give a brief explanation of the result.

5. As we will soon see, de Broglie taught us to associate
a wavelength lambda = h/p with the probability amplitude 
of a particle with momentum p. (h is Planck's constant.)
(Note that this is the same as the relation that we alresdy
have for photons.) Atoms have a size of roughly 0.1 nm. Using that,
discuss Feynman's claim on pages 1-4,5 that it is difficult
to actually do the 2-slit experiment with electrons.

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Problem set 2  due 9am Tuesday, 15 April 
in the locked boxes at the back of our lecture, 55 Ro.

1. One piano wire is 1m long and tuned to 440Hz. Another has 
the same wave speed but is 2mm longer. What is the beat 
frequency when they are played together?

Q1: B.7

Q2: B.2 S.3 S.4

I think Eq. Q1.14 is incorrect if k=pi/L. Do you agree? 
Why or why not? What is the correct expression?

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Problem set 1  due 9am Tuesday, 8 April 
in the locked boxes at the back of our lecture, 55 Ro.

See "Problem set 1" on the website.

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