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Question: A charge Q is placed at the centre of the line joining two point charge +q and +q as shown in figure...

A charge Q is placed at the centre of the line joining two point charge +q and +q as shown in figure. The ratio of charges Q and q is

A

4

B

1/4

C

-4

D

-1/4

Answer

-1/4

Explanation

Solution

: For the system to be in equilibrium, net force on q = 0 Electric charges and Fields

or Qq4πε0x2+qq4πε0(2x)2=0\frac{Qq}{4\pi\varepsilon_{0}x^{2}} + \frac{qq}{4\pi\varepsilon_{0}(2x)^{2}} = 0

or Q=−q4Q = \frac{- q}{4} or Qq=−14\frac{Q}{q} = - \frac{1}{4}