Question

Two tiny, identical, equally charged, insulating balls each weigh 0.1 g and hang from a common point by identical light strings 0.3m long. The balls repel each other, so that their separation is 8 cm. What is the magnitude of the charge on each ball? What can you say about the signs of each of these charges?

Answer 1

Given:

Mass of each ball

Length of each string

Separation between the balls

Solution:

Let the magnitude of charge on each ball is .

The electric force of repulsion between the two balls is given by

From the free body diagram of one of the balls it is clear that

Dividing the two equations we get

Answer:

Magnitude of the charge on each ball

The two charges are either both positive or both negative.