Question

Two parallel conducting plates of area each are placed 6 mm apart and are both earthed. A third plate, identical with the first two, is placed at a distance of 2 mm from one of the earthed plates and is given a charge of 1 C. The potential of the central plate is.

• A.
• B.
• C.
• D.

Answer 1

Answer: (A)

Answer 2

: The plates 1 and 2 will form one capacitor and plates 2 and 3 will form another capacitor. These two capacitors are in parallel. Their effective capacitance is

Potential of central plate, $\mathrm { V } = \frac { \mathrm { Q } } { \mathrm { C } } = \frac { \mathrm { Q } 2 \mathrm {~d} } { 3 \varepsilon _ { 0 } \mathrm {~A} }$

$= \frac { 1 \times 2 \times 2 \times 10 ^ { - 3 } } { 3 \times 8.85 \times 10 ^ { - 12 } \times 2.5 } = 6 \times 10 ^ { 7 } \mathrm {~V}$