Question

A parallel plate condenser is immersed in an oil of dielectric constant 2. The field between the plates is :

• A. increased, proportional to $\frac{1}{2}$
• B. decreased, proportional to -2
• C. increased, proportional to -2
• D. decreased, proportional to $-\frac{1}{2}$

Answer 1

The correct option is D decreased, proportional to $-\frac{1}{2}$

Let before immersed in oil the capacitance is $C$ , potential is $V$.
and field , $E=V/d$ where $d=$ separation of plates.
After immersed in oil the capacitance becomes $C^{\prime }=kC=2C$ and potential becomes $V^{\prime }=V/2$ becasuse $C=\frac{Q}{V}$.
Now filed , $E^{\prime }=V^{\prime }/d=\frac{1}{2}\left(V/d\right)=\frac{E}{2}$