Question

The electric field, at a distance of 20 cm from the centre of a dielectric sphere of radius 10 cm is 100 V/m. The ‘E’ at 3 cm distance from the centre of sphere is

• A. 100 V/m
• B. 125 V/m
• C. 120 V/m
• D. Zero

Answer 1

Answer: (C)

120 V/m

Answer 2

For dielectric sphere i.e. for non-conducting sphere

$E_{out} = \frac{k.q}{r^{2}}$ and $E_{in} = \frac{kqr}{R^{3}}$

$E_{out} = 100\frac{KQ}{(20 \times 10^{- 2})^{2}}$ ⇒ KQ = 100 × (0.2)² so $E_{in} = \frac{100 \times (0.2)^{2} \times (3 \times 10^{- 2})^{2}}{(10 \times 10^{- 2})^{3}}$= 120 V/m