JEE PYQ: Electrostatics Question 28
Question 28 - 2020 (06 Sep Shift 2)
Consider the force F on a charge ‘$q$’ due to a uniformly charged spherical shell of radius $R$ carrying charge $Q$ distributed uniformly over it. Which one of the following statements is true for F, if ‘$q$’ is placed at distance $r$ from the centre of the shell?
(1) $F = \frac{1}{4\pi\varepsilon_0}\frac{Qq}{R^2}$ for $r < R$
(2) $\frac{1}{4\pi\varepsilon_0}\frac{Qq}{R^2} > F > 0$ for $r < R$
(3) $F = \frac{1}{4\pi\varepsilon_0}\frac{Qq}{R^2}$ for $r > R$
(4) $F = \frac{1}{4\pi\varepsilon_0}\frac{Qq}{R^2}$ for all $r$
Show Answer
Answer: (3)
Solution
For a uniformly charged shell: $F = 0$ for $r < R$ (no field inside). $F = \frac{1}{4\pi\varepsilon_0}\frac{Qq}{r^2}$ for $r > R$. At $r = R$: $F = \frac{1}{4\pi\varepsilon_0}\frac{Qq}{R^2}$. So option (3) is correct for $r > R$ at $r = R$.
BETA
