Question

A small charge pith ball is suspended2 cm above a second charge pith ball resting on an insulated surface. If the charge of the lower ball is +20 stat C and it has a mass of 0.25 g, what must be the on the upper ball to lift the lower ball?

Answer 1

Answer:

49

Explanation:

To lift the lower pith ball, the net force acting on it should be zero. Therefore gravitational force (in downward direction) acting on it must be equal to the Coulomb attraction force (in upward direction) exerted on it by the upper pith ball.

As those two balls attract each others, their charge must be opposite. As the lower ball has +ve charge on it, charge on the upper ball is negative.

Let the charge on upper ball be q

Hence, 0.25*980=(20*q)/2^2

or, q=49

Charge on the upper ball is -49 statC