Question

A capacitor is made with a polymeric dielectric having an ϵr of 3 and a dielectric breakdown strength of 60 kV/cm. The permittivity of free space is 8.85 × 10-12 F/m. If the rectangular plates of the capacitor have a width of 15 cm and a length of 35 cm, then the maximum electric charge on the capacitor is ________ 
1. 5 μC
2. 10 μC
3. 15 μC
4. 9 μC

Answer 1

Correct Answer - Option 4 : 9 μC

Concept:

\(C = \frac{{{\epsilon_0}{\epsilon_r}A}}{d}\)

Q = CV

\(= \frac{{{\epsilon_0}{\epsilon_r}AV}}{d}\)

Analysis:

Maximum electrical charge on the capacitor,

when,

 \(\left( {\frac{V}{d}} \right) = {\left( {\frac{V}{d}} \right)_{max}} = 60 \times kV/cm = 60 \times {10^3} \times {10^2}V/m\)

Q = 8.85 × 10-12 × 3 × 15 × 10-2 × 35 × 10-2 × 60 × 103 × 102

= 8.36 μC