In fig. `C_(1) = 20 muF, C_(2) = 30 muF and C_(3) = 15 muF` and the insulated plate of `C_(1)` is at a potential of 90 V, one plate of `C_(3)` being earthed. What is the potential difference between th plates of `C_(2)` three capacitors being connected in series ?

Options

A. 10 e.s.u.
B. 30 e.s.u.
C. 40 e.s.u.
D. 20 e.s.u.

Answer

D

Explanation

`C_(1)=20esu, C_(2)=30esu,C_(3)=15esu,`
`V=90esu, V_(2)=?`
`1/C_(s)=1/C_(1)+1/C_(2)+1/C_(3)`
`=1/20+1/30+1/15=(3+2+4)/60`
`C_(s)=60/9esu`
Now `V_(2)=Q/C_(2)=(C_(s)*V)/C_(2)=60/9xx90/30`
`V_(2)=20esu`