# Q. Charges -q and +q located at A and B, respectively, constitute an electric dipole. Distance AB = 2a, O is the mid point of the dipole and OP is perpendicular to AB. A charge Q is placed at P where OP = y and y >> 2a. The charge Q experiences and electrostatic force F. If Q is now moved along the equatorial line to P' such that OP' = $\left(\frac{y}{3} \right)$ , the forece on Q will be close to : $\left(\frac{y}{3} > > 2a\right)$

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Solution:

## Electric field of equitorial plane of dipole $= - \frac{K\vec{P}}{r^{3}}$ $\therefore At P,F = \frac{K\vec{P}}{r^{3}} Q.$ $At P^{1} , F^{1} = - \frac{K\vec{P}Q}{\left(r/3\right)^{3}} = 27F$

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