Question

A parallel plate condenser with oil (dielectric constant 2) between the plates has capacitance C. lf oil is removed, the capacitance of capacitor becomes

• A. $\sqrt 2\,C$
• B. 2C
• C. $\frac {C}{\sqrt 2}$
• D. $\frac {C}{2}$

Answer 1

Answer: (D)

$\frac {C}{2}$

Answer 2

The capacitance of a parallel plate capacitor with dielectric
(oil) between its plates is

$C = \frac {K \varepsilon_0 A}{d} \, \, \, \, \, \, \, ...(i)$
When dielectric (oil) is removed, so capacitance
$C_0 = \frac {\varepsilon_0 A}{d} \, \, \, \, \, \, \, ...(ii)$
Comparing Eqs. (i) and (ii), we get
$\, \, \, \, \, \, \, \, \, \, \, \, C = KC_0$
$\Rightarrow \, \, \, \, \, \, \, C_0 = \frac {C}{K} = \frac {C}{2} \, \, \, \, \, \, (\therefore k = 2)$