Magnitude of an electric field?

Question

What is the magnitude of an electric field that balances the weight of a plastic sphere of mass 9.0g that has been charged to -3.0 nC?. 

A) 9.0 × 10^6 N/C B) 6.3 × 10^6 N/C C) 3.3 × 10^6 N/C D) 2.9 × 10^7 N/C 

Answer 1

Electrical field is force per charge ratio.

Given,

Mass of the sphere m  = 9 g = 9×10^-3 kg

Charge, q = - 3 nC = -3×10^-9 C

Calculate the weight of the sphere.

F = mg

    = (9×10^-3) (9.81)

    = 0.08829 N

Calculate the magnitude of the electrical field ,

E = F / q

   = 0.08829 / -3×10^-9

    = -2.9×10⁷ N/C

Therefore, the option D is correct.