Sample Essay Questions

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Current by Jason T Hardy
on Aug 29, 2007 23:58.

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Makeup examinations consist entirely of three essay questions and students must answer all three. Makeup examinations have no multiple-choice component and no choice of questions, and makeup examination essay questions are more difficult than regular examination essay questions.

* The photoelectric tube we studied in class last week has some unusual properties as a circuit element, including behaving for some voltages as if it had a negative resistance". (Note: By "negative resistance" I mean that for some values of V, "R" = V/I is negative. On our IV curve for the phototube we actually had positive current at a slightly negative voltage.) What is the difference between what is happening to the conduction electrons in the photoelectric tube as compared to what happens to them in a resistor?
* Describe briefly Rutherford's experiment probing the structure of the atom and explain why the result was a surprise.
* A researcher tells you that within a 10 second window, a single electron will hit the television screen you are viewing. Sure enough, there is a flash within that time window. The researcher told you nothing else, though, and so you don't know the experimental setup being used. You only know that she has a gizmo that allows the release electrons at long time intervals. Do you know if that electron went through a two-slit interference apparatus or if it was simply shot at the screen? Explain how you arrive at your answer.
h2. Sample Questions (All were used in previous sections of this course)

* An electron and a proton of identical energy are incident on the same potential barrier. If the probability of transmission for the electron greater than, less than, or equal to the transmission probability of the proton? Explain how you arrived at your answer.
* What is the difference between a conductor and an insulator? Give experimental evidence for the descriptions that you give, and try to account for these descriptions using a microscopic model of the material.
* Based on the model we have been describing in class, how could you account for the difference between a conductor and a resistor... Explain.
* How, if at all, can you account for the different conductivity values of different types of metals? Does copper conduct better, or does iron? How do you know? Explain how you think about the situation.
* An LED (light emitting diode) is a device like the one in your VCR remote control and many other appliances. When observed, it seems to shine in only one color. Is there a filter in the glass or is it a property of the device? Explain how you could account for the observation, based on what you know about the device. If you don't know anything about LEDs (I'm guessing that's the case for many of you), tell me, and then STILL try to figure out what might be going on. Use your everyday physics thinking on this one, if you don't know the formal response...
* We have talked about the LED and we have talked about polarization of metals. Compare and contrast the two. Compare the "current" electrons in the case of the LED and the polarized metal. What are the similarities and what are the differences? How do you know? Explain in as much detail as possible.
* Do you think a photon is more like a wave or more like a particle? Explain why you think so.
* In the infinite square well potential, there are often places (in excited states) where the probability of finding a particle is zero. Does that mean that a particle can't move through that location? Explain (i.e. explain how we can measure the location in one probable area, then later measure it in another probable area separated by a place where the probability was zero).
* You have a friend taking this class at another university, and her class is slightly ahead of this one. She calls you up one day and says, "You won't believe my crazy prof, he's so funny and always has us laughing. It's the greatest. But you know what he told me? He said that there's nothing we can do about it, quantum mechanics is the real way of thinking about the world, and all that stuff we learned in our intro classes was all wrong." What do you tell her, should she agree with the prof or not? Do you? Back up your answer with examples from your previous studies of physics.
* When did you first learn about electrons and that electrons were particles which were parts of atoms? Elementary school, high school, college? From teachers, from magazines, from TV? Do you even remember when you learned it? How do you know that it's true? This is one of those questions to help me see where you stand, so you don't have to say too much. I'm just curious when and how you learned some of the things you're bringing to class.
* A friend of yours is taking a class like this one at another school. She calls you up one day and you get to talking about your classes. She says, "we just talked about the probability of finding particles in a potential well, and I think I figured it out. Whaddya think, the particle is always located somewhere, but we sometimes simply can't measure it. Even if we're not always paying attention to it, it's still located somewhere, right? That makes sense to me..." What do you tell her? Do you agree? disagree? Be as thorough and explicit as possible.
* A friend (not the same one who has stopped calling you, a different one...) talks to you in the hallway of the student union. You're being nerdy and talking about conduction in wires. He says the following, "When I have a wire, and it's not in an electric field or anything, it doesn't have any current, so there are no free electrons. There aren't any in the wire until an electric field, you know, a voltage or something, is on the thing. Then you get free electrons." Does his thinking agree with yours? How is it similar, how is it different? If it is similar, explain in more detail what your friend might be saying. If it is different, explain how you think about the existence of free electrons in a metal.
* A friend in your math class tells you that when doing quantum mechanics you don't have to think about classical things at all. It's either quantum or it isn't. When you do quantum, you just have to toss your intuition out the window and let the math and the weird stuff take over. Rather than simply reacting to this statement, I want you to give me TWO examples. As part (a), give me an example where your friend is CORRECT, and you had to suspend all understanding of classical mechanics in order to think about the quantum physics. In part (b), give an example where your friend is INCORRECT, and you had to use your classical reasoning to help you with the quantum mechanics.