PHYSICS 232
Midterm 1, February 21 , 1997, 5:30pm-6:45pm
Instructor: P. Q. Hung

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

Useful formulas (not necessarily applied to all problems below):

1) Two volley balls, mass 0.3 kg each, tethered by nylon strings and charged with an electrostatic generator, hang as shown in the figure. What is the charge on each, assuming the charges are equal.

Let's look at the force diagram for one ball.

[eq1]

[eq2]

[eq1]+[eq2]

2) Three conducting plates are placed parallel to one another as shown. The outer plates are connected by a wire. The inner plate is isolated and carries a charge amounting to 10 nC (1 nC = C) per square centimeter of plate. In what proportion must this charge divide itself into a surface charge on one face of the inner plate and a surface charge on the other side of the same plate?

The electric fields looks like

where