Positive charge  Q is distributed over a circular Ring of radius a. A point particle of massm & negetive charge -q, is placed on its Axis at a distance y from the centre. Find force on particle. Option 1) $\frac{kQ}{a^2}$ Option 2) $\frac{kqyQ}{a^3}$ Option 3) 0 Option 4) $\frac{kQy}{a^3}$

A Avinash

As we have learnt,

E and V at a point P that lies on the axis of ring -

$\dpi{100} E_{x}=\frac{kQx}{\left ( x^{2}+R^{2} \right )^{\frac{3}{2}}}$  ,   $\dpi{100} V=\frac{kQ}{\left ( x^{2}+R^{2} \right )^{\frac{1}{2}}}$

-

As $E = \frac{kQ}{(a^2 + R^2)^{\frac{3}{2}}}\Rightarrow F = qE$

Putting values

$F = \frac{kQqy}{a^3}$

Option 1)

$\frac{kQ}{a^2}$

Option 2)

$\frac{kqyQ}{a^3}$

Option 3)

0

Option 4)

$\frac{kQy}{a^3}$

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