PHYSICS 232
Midterm 2, March 28 , 1997, 5:30pm-6:45pm
Instructor: P. Q. Hung

25 points for each problem. READ the problems carefully. SHOW CLEARLY YOUR WORK. DO NOT JUST write the answers down. ANSWERS WITHOUT EXPLANATION WILL BE GIVEN NO CREDIT.

Useful formulas from Midterm 1 in addition to your formula sheet:

1) The magnetic flux through the loop shown in the figure below (B out of the plane) increases according to the relation where is in milliwebers and t is in seconds. (a) What is the magnitude of the emf induced in the loop when t= 2.0 s? (b) What is the direction of the current through R?

a)

At t=2.0s,

b) Flux is increasing out of page

current induced clockwise

current passes through resistor from right to left

2) A straight conductor carrying a current I = 5.0 A splits into identical semicircular arcs of radius r = 5 cm as shown in the figure below. What is the magnetic field at the center C of the resulting circular loop?

No contribution from the straight parts of the wire. Splitting the wire into two semicircles, we look at the top semicircle:

(into the page)

For the bottom semicircle, we have

(out of the page)

resulting in

Therefore,