Question

The distance between the circular plates of a parallel plate condenser $40mm$ in diameter, in order to have same capacity as a sphere of radius $1\mspace{6mu} metre$is

• A. $0.01mm$
• B. 0.1 $mm$
• C. 1.0 $mm$
• D. 10 $mm$

Answer 1

Answer: (B)

0.1 $mm$

Answer 2

$4\pi\varepsilon_{0}r = \frac{\varepsilon_{0}A}{d}$ ⇒ $d = \frac{A}{4\pi r} = \frac{\pi(20 \times 10^{- 3})^{2}}{4\pi \times 1} = 0.1mm$