Question

A parallel plate capacitor has area $20c{m}^2$ and separation between the plates is $0.1mm$. The dielectric break down strength is $3\times {10}^6$$v/m$. The maximum r.m.s voltage which can be safely applied is :

• A. $210V$
• B. $300V$
• C. $100V$
• D. $200$

Answer 1

The correct option is A $210V$

Above a particular electric field, of dielectric strength say $E_{ds}$, the dielectric in a capacitor becomes conductive. The voltage at which this occurs is called the breakdown voltage of the device, and is given by the product of the dielectric strength and the separation between the conductors.
Thus we get $V_{bd}=E_{ds}d$
Thus we get
$E_{ds}=3\times {10}^6=\frac{V_{bd}}{d}$
or $V_{rms}=\frac{V_{bd}}{\sqrt{2}}=\frac{3\times {10}^6\times {10}^{-4}}{\sqrt{2}}=210V$