Three capacitors having capacitances of `8.4 muF, 8.2muF` and `4.21muF` are connected in series across a 36 potential difference.
(a) What is the charge on `4.2muF` capacitor?
(b) What is the total energy stored in all three capacitors?
(c) The capacitors are disconnected from the potential difference without allowing them to discharge. They are then reconnected in parallel with each other, with the positively charged plates connected together. What is the voltage across each capacitor in the parallel combination?
(d) What is the total energy now stored in the capacitors?

Answer

A, B

Explanation

a. `1/C_(n et)=1/8.4+1/8.2+1/4.2`
`:.C_(n et)=2.09muF`
`q_(n et)=C_(n et)V`
`=(2.09)(36)`
`=75.14muC=76muC`
in series charge remains same in all capacitors.
b. `U_("total")=1/2C_(n et)V^2`
`c. q_("total")=(3)(76)muC=288muC`
Now common potential in parallel.
`V=q_("total")/C_("total")=(228muC)/((8.4+8.2+4.2)muF)`
`d. U_("total")-=1/2C_(n et)V^2`