Three plates `A, B, C` each of area `50 cm^(2)` have separation `3 mm` between `A` and `B mm` between `B` and `C`. The energy stored when the plates area fully charged is

Options

A. `1.6 xx 10^(-9) J`
B. `2.1 xx 10^(-9) J`
C. `5 xx 10^(-9) J`
D. `7 xx 10^(-9) J`

Answer

B

Explanation

There are two capacitors parallel to each other.
`:.` Total capacitance `= (2epsilon_(0)A)/(d)`
`:.` Energy stored ` = (1)/(2) ((2epsilon_(0)A)/(d)) V^(2)`
`= (8.86 xx 10^(-12) xx 50 xx 10^(-4) xx 12^(2))/(3 xx 10^(-3)) = 2.1 xx 10^(-9) J`