Physics 360 Questions on the final



Question: In problem #3, you forbid finding the B-field using current configuration.
 Should I NOT use the Biot-Savart law?  Should I find the Vector Potential
A? I understand if the second question cannot be answered, but I AM
concerned about the ambiguity of question #3.  Thank you.

Answer: You are not to use any RESULTS for any current configuration.  For example, you are not to look up the field due to a straight wire segment, which is done as an example in both Griffiths and Lea and Burke, and use the formula.  Rather you are to calculate from first principles using the Biot-Savart Law for a wire segment dl or a current j d(volume).

Question: In problem 4, can we assume that the particle has a mass, m?
Answer: Yes

Question
 I noticed you stated "a uniform E-field...a large distance from the cylinder".  I just assumed a uniform E-field throughout, even around the location of the cylinder, or are we suppose to treat that differently.

Answer
The field is uniform everywhere before the cylinder is put in place.  Afterward it remains unchanged a great distance from the cylinder, but not necessarily anywhere else.

Question.
I was wondering if it's ok to reference our calculator for doing an integral.

Answer:
Only if you absolutely have to. The one integral you need to do is pretty easy, actually. You "just" need the right substitution! But if you run out of time and you still don't have it, use the calculator. A calculator is just a small computer, so technically is forbidden by the rules of the exam.  You won't get the points for doing the integral, but you will get the points for the answer.