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Three point charges 4q, Q and q are plac...

Three point charges 4q, Q and q are placed in a straight line of length L at points 0, L/2 and L respectively. The net force on charge q is zero. The value of Q is

A

4q

B

`-q`

C

`-0.5q`

D

`-2q`

Text Solution

Verified by Experts

The correct Answer is:
B

`because` Net force on charge, q=0
`rArr f_(1) + f_(2)= 0` …(i)
Here, `f_(1)` is the force on charge q due to charge 4q `f_(2)` is the force on charge q due to charge Q
`therefore` From eq (i),
`rArr (K(4q)q)/(L^(2))+ (KQq)/((L//2)^(2))=0`
`rArr 4q^(2)+4Qq=0`
`rArr Q=-q`
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