Question

A ring of radius R is charged uniformly with a charge +Q. The electric field at a point on its axis at a distance r from any point on the ring will be:-

• A. $\frac{KQ}{\left(r^2-R^2\right)}$
• B. $\frac{KQ}{r^2}$
• C. $\frac{KQr}{r^3}{\left(r^2-R^2\right)}^{\frac{1}{2}}$
• D. $\frac{KQr}{R^3}$

Answer 1

The correct option is A $\frac{KQ}{\left(r^2-R^2\right)}$

form Charge Q, at distance x ,electric field:

$E=\frac{kQ}{x^2}$ ---eq.1

$r^2=R^2+x^2$

from eq.1

$E=\frac{kQ}{r^2-R^2}$

Hence option 'A' is correct.