Question

Two charge 5 milli coulomb and -4 milli coulomb are kept 5.0
m apart at points A and B respectively.
How much work will have to be done to
move the charge at A through a distance
of 5.0 m further away from point B along the line BA​

Answer 1

Answer:

Lets say charge 'B'(Q = -4μC) is fixed as and 'A'(q = 5μC) is moved. We think of this situation as moving charge A in the B's electric field.

Work done in moving a charge in electric field, W = qΔV

q = 5μC

W = q(Vf - Vi)

Vf = KQ/Rf = (9*10⁹ x -4*10⁻⁶)/10m = -3600V

Vi = KQ/Ri = (9*10⁹ x -4*10⁻⁶)/5m = -7200V

ΔV = Vf - Vi = -3600V- (-7200V) = 3600V

W = qΔV = 5μC x 3600V = 18mJ = 1.8x10⁻⁴ J

Work in moving A in the electric field of B,

W =  1.8x10⁻⁴ J