The equivalent capacitances of the combination between points A and B in the given figure is `4muF`.

(i) Calculate capacitance of the capacitor C.
(ii) Calculate charge on each capacitor, if a 12 V battery is connected across terminals A and B.
(iii) What will be the potential drop across each capacitor ?

Explanation

According to the question, `20muF` and C are connected in series.
(i) The equivalent capacitances
`(4muF)=((20muF)xxC)/(20+C)`
`(20+C)=5C`
or 4C = 20
`:." C "=5muF`
(ii) Both capacitors are connected in series, so charge on both of them will be same and will be equal to the total charge.
`:.` Charge on each capacitor,
`Q=CV=4xx12`
`=48muC`
Same charge `48muC` lines on both the capacitors
(iii) Potential drop across `20muF` capacitor is given by
`V_(1)=(Q)/(C_(1))=(48muC)/(20)=2.4V`
Potential drop across `5muF` capacitor is given by
`V_(2)=(Q)/(C_(2))=(48muC)/(5)=9.6V`