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A point charge -q is carried from a poin...

A point charge -q is carried from a point A to anther point B on the axis of a charged ring of radius r carrying a charge +q. If the point A is at a distance `4/3 r` from the centre of the ring and the point B is `3/4 r` from the centre but on the opposite side, what is the net work that need to be done for this

A

`-7/5 (q^2)/(4pi epsilon_(0)r)`

B

`-1/5 (q^2)/(4pi epsilon_(0)r)`

C

`7/5 (q^2)/(4pi epsilon_(0)r)`

D

`1/5 (q^2)/(4pi epsilon_(0)r)`

Text Solution

Verified by Experts

The correct Answer is:
B
Net work done (W) = electric potential energy at point B - electric potential energy at point a

`or, W = 1/(4 pi epsilon_(0)) cdot ((+q)(-q))/(sqrt(r^(2)+(3/4 r)^(2))) - 1/(4 pi epsilon_(0)) cdot ((+q)(-q))/(sqrt(r^(2)+(4/3 r)^(2))) - 1/(4 pi epsilon_(0))`
`= -1/5 cdot (q^2)/(4 pi epsilon_(0)r)`.
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