(2) (a) Find the potential difference between a point located a distance r from

Question

(2) (a) Find the potential difference between a point located a distance r from a positive point charge, +q, located at the origin and a point located very far away.

(b) Find the potential difference between a point located a distance r away from a positive point charge, +q, located at a point R away from the origin in the x-direction.

(c) Imagine a situation where both these charges exist. Describe the surface where the total potential is zero.

(d) Describe the surface where the total electric field is zero.

Explanation / Answer

a) potential due to point charge at distance r is given as

V = kq/r

when point is far far away then V = 0

deltaV = kq/r

b) Vr = kq/r

VR = kq/R

delatV = VR - Vr = kq [ 1/R - 1/r]   = kq(r - R) / rR

c) potential at point distance r1 from q1 and r2 from q2 then

kq1/r1 + kq2/r2 = 0

q1/r1 = - q2/r2

this will be inifinite plane perpendicular to the line joing charges.

d) E = kq/r^2

hence kq1/r1^2 = - kq2/r2^2

q1/r1^2 = - q2 / r2^2

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