HW2-1

The excess negative charge on the shoe soles repels the negative ions in the body and on the skin, forcing them to the upper extremities of the body, including onto the fingers. When the finger is brought near the door knob, the door knob is polarized, which in turn, polarizes the finger even more, and it together with the finger provides enough force on free electrons in the air to cause them to accelerate enough to knock electrons off atoms they bang into, causing a chain reaction that knocks electrons off lots of atoms. Each time an electron is knocked off an atom, it emits light. When there are enough reactions, the light is visible. Once you get close enough to discharge the finger by grounding on the doorknob, the reactions cease.

HWK 2-2

HWK 2-3 BIGGER!

HWK 2-4

HWK 2-5

HWK 2-6.

a) Have: two identical metal balls
q1 = q2 = 0.5 x 1010 e.
r = .2 m
Assumptions:
Both balls share charge equally
All charge behaves as if it is located at the center of the balls
Distance between balls that polarization can be ignored.

F = kq1q2 / (0.2 m)2 = 1.44 x 10-7 N

b) When the two spheres are close together relative to their diameters, the negative charges on each sphere repel each other so that the center of excess charge on each ball is shifted away from the center of the spheres, so that the distance between the "average" location of total charge on the two spheres is a further distance than the distance between the centers of the two spheres.

HWK 2-7.

a) Positive glass rod attracts some of the excess electrons to the top, leaving the charge on the gold foils net positive, so they repel each. b) Charging by contact leaves like charge. Since the foils move closer together, moving the electroscope near the positively charged rod attracted electrons from the leaves to the ball. The leaves had to have excess electrons, hence the metal ball was charged negatively.

HW2-9: We will present particular solutions, but these are not the only valid schemes.

Hwk 2-10

I'm not going to tell you!

Just use page 43 in C&S as a guide and figure it out.