Question

A parallel plate air capacitor is charged to a potential difference of V volts. After disconnecting the charging battery the distance between the plates of the capacitor is increased using an insulating handle. As a result the potential difference between the plates.

• A. Increases
• B. Decreases
• C. Does not change
• D. Becomes zero

Answer 1

Answer: (A)

Increases

Answer 2

$\mathrm { F } = \varepsilon _ { 0 } \frac { \mathrm { V } ^ { 2 } } { \mathrm {~d} ^ { 2 } } \pi \mathrm { r } ^ { 2 }$

If the disc is to be lifted,

i.e., $\varepsilon _ { 0 } \frac { \mathrm { V } ^ { 2 } } { \mathrm {~d} ^ { 2 } } \pi \mathrm { r } ^ { 2 } = \mathrm { mg }$ (for minimum V)

$\therefore \mathrm { V } = \sqrt { \frac { \mathrm { mgd } ^ { 2 } } { \pi \varepsilon _ { 0 } \mathrm { r } ^ { 2 } } }$