Hints for Assignment 8

41. You usually prove a negative statement by assuming that the statement is true and reasoning your way to a statement that you know is untrue. If the reasoning is correct, then the initial assumption had to be false.

42. Draw in the forces. Don't take anything out of an integral that depends on the integration parameter.

43. The hint is given in the problem. Under no circumstances should you attempt to integrate the Biot-Savart Law over the current distribution, and the complete current distribution does not have any usable symmetry. Follow the hint. Superposition is the key word.

In part (c), it is possible to get the answer without a great deal of algebra by a clever use of vectors.

44. Can you say "sum over loops"? Let the thickness of the wire be small compared to the length of the coil. (Why?) This problem shows why we would rather use Ampere's Law than do the sum over loops explicitly.

45. Follow the instructions.

Return to Assignment

Last revised 1998/03/29