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 ?

Answer

20 V

Explanation

The equivalent capacitance of the series combination is fig.

`(1)/(C ) = (1)/(C_(1)) + (1)/(C_(2)) + (1)/(C_(3)) = (1)/(20) + (1)/(30) + (1)/(15)`
`= (3)/(20) , C = (20)/(3) muF`
Total potential diff. `V = 90- 0 = 90 V`
Total charge, `q = CV = ((20)/(3) xx 10^(-6)) xx90`
`= 600xx10^(-6) C`
Potential diff. between plates of `C_(2)`
`V_(2) = (q)/(C_(2)) = (600xx10^(-6))/(30xx10^(-6)) = 20 V`