An insulating sphere of radius 0.140m has uniform charge density 8.00*10^(-9)C/m

Question

An insulating sphere of radius 0.140m has uniform charge density 8.00*10^(-9)C/m^3 . A small object that can be treated as a point charge is released from rest just outside the surface of the sphere. The small object has positive charge 4.50*10^(-6)C

How much work does the electric field of the sphere do on the object as the object moves to a point very far from the sphere? Express your answer to three significant figures and unit.

A charged paint is spread in a very thin uniform layer over the surface of a plastic sphere of diameter 15.0cm , giving it a charge of -13.0?C

Find the electric field 6.50cm outside the surface of the paint layer. Express your answer to three significant figures

Explanation / Answer

Work done = V*Q where V is the potential at the surface of the sphere and Q is the positive charge

V = 9*10^9 * [8*10^(-9) * (4pi/3)*.14^3]/.14 = 5.911 V

Work done = 5.911*4.5*10^-6 = 26.6 uJ

I am unable to see the units of charge of paint and I am doing it considering it as nC

Electric field = k*Q'/r^2 = 9*10^9 *(-13*10^-9 + (8*10^-9 * (4pi/3)*.14^3))/(.14+.065)^2 = -8.15 N/C

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