HWK1-1. Students should give a careful discussion of method of attack. (3 points)

Calculating the number of excess (or deficit) electrons on the U tape.

We plan to use force of gravity which we can calculate, and newton's second law, or the equilibrium principle, to help us determine the electric force. We will use two U tapes, that way we'll know that the charge on the two pieces of tape are approximately the same, enabling us to use the following calculations to obtain the charge on one of the tapes.

The big picture: (3 points)

from whence, F_E = mgx/y = kq²/d², so

3 points

The number of excess (or deficit) electrons on the tape is n = q/1.6x10^-19C/e

(this value should be approximately 10⁸)

Data taken: 3 points

mass of tape m = .2 g = .2x10^-3kg

x = __________

y = __________

z = __________ (if used to find x or y)

d = __________

HWK 1-2. To find the ratio of excess electrons to molecules on the surface we need to obtain the number of molecules on the surface, and divide the number of excess electrons by this number.

2 points

The number of molecules on the surface of the tape is obtained by

HWK1-3: (1 point) Should discuss how your density compares with 5x10^-5 C/m²