Q 12-01-008NEETNEET 2020Top questionEasy
A spherical conductor of radius $10$ cm has a charge of $3.2 \times 10^{-7}$ C distributed uniformly. What is the magnitude of electric field at a point $15$ cm from the centre of the sphere ? $\left(\dfrac{1}{4\pi\epsilon_0} = 9 \times 10^9\ \text{N m}^2/\text{C}^2\right)$
Answer: (B) $1.28 \times 10^5$ N/C
The point is outside the sphere, so the charge acts as if concentrated at the centre:
$$E = \frac{kq}{r^2} = \frac{9 \times 10^9 \times 3.2 \times 10^{-7}}{(0.15)^2} = \frac{2880}{0.0225} = 1.28 \times 10^5\ \text{N/C}$$
Solution by Sreeraj P, M.Sc Physics