Question

Capacity of a parallel plate condenser is 10μF when the distance between its plates is 8 cm. If the distance between the plates is reduced to 4cm, its capacity will be

• A. 10μF
• B. 15μF
• C. 20μF
• D. 40μF

Answer 1

Answer: (C)

20μF

Answer 2

$C = \frac { \varepsilon _ { 0 } A } { d } \propto \frac { 1 } { d }$∴$\frac { C _ { 1 } } { C _ { 2 } } = \frac { d _ { 2 } } { d _ { 1 } }$ or

$C _ { 2 } = \frac { d _ { 1 } } { d _ { 2 } } \times C _ { 1 } = \frac { 8 } { 4 } \times 10 = 20 \mu \mathrm { F }$