A `5muF` capacitor is placed across a 12 V battery. It is disconnected from the battery and connected across a condenser of unknown capacity. The voltage then is found to be 3V. The value of the unknownn capacity is

Options

A. `5muF`
B. `10muF`
C. `15muF`
D. `20muF`

Answer

C

Explanation

`Q=c_(1)v_(1)=5xx10^(-6)xx12=60xx10^(-6)C`
when it is connected in parallel with another capacitor
`(c_(2))` theire resultant capacity `=c_(1)+c_(2)` but the charge remains the same
`therefore (c_(1)+c_(2))V=q" "therefore (c_(1)+c_(2))xx3=60xx10^(-6)`
`therefore c_(1)+c_(2)=20xx10^(-6)" "therefore c_(2)=15xx10^(-6)F`