Repulsion of Charged Pith Balls

separation

1.

length

1.

mass

0.005

Two equally charged pith balls of equal mass are separated by a distance

r

, due to their mutual electrostatic repulsion. Each ball hangs on a string of length

l

from a common point, making an angle

θ

with the horizontal. The value of the angle

θ

, the charge

q

, and the tension

T

of the string are calculated.

By trigonometry, the angle is equal to

-1

cos

(r/2l)

, the value of the charge is

2

r

mg/(ktanθ)

, and the tension is

mg/sinθ

, where

g

is the acceleration of gravity and

k

is the constant in Coulomb's law.

Enrique Zeleny