Question

A tiny ball (mass = 0.010 kg) carries a charge of -24C. What is the electric field magnitude that would cause the ball to float above the ground?

Answer 1

Use the relation between electric force and electric field and the concept of gravitational force to calculcate the electric field. The electric force is given by

`F_e = qE`

And the gravitational force is

`F_g = mg`

For the ball to float above the ground, the magnitude of electric force on the ball must be equal to the magnitude of the gravitational force. That is must be a equilibrium condition, so,

`F_e = F_g`

`qE = mg`

`E = (mg)/(q)`

Replacing the values we have that,

`E = ((0.010)(9.8))/(-24*10^(-6))`

`E = -4.083*10^(3) N/C`

Therefore the electric field magnitude that would cause the ball to float above the ground is
`-4.083*10^(3) N/C`