Question

A parallel-plate capacitor is charged by a 18.0 V battery, then battery is removed.

What is the potential difference between the plates after the battery is disconnected?

What is the potential difference between the plates after a sheet of Teflon is inserted between them?

What is the power output of the charger in watts?

Answer 1

1.

After disconnecting the battery the charge on the plates of the capacitor remains same and also potential difference will not change.
that is the potential difference is now 18V .

2.

The charge when the battery is removed Q = C*V

charge when battery is removed after inserting Teflon Q' = C'*V'

The dielectric teflon does not increase the charge but changes the capacitance and potential difference between the parallel plates ,

Q' = Q

and , C' = C/k

Q' = C'*V'

Q = k*C*V'

V' = Q/k*C

V' = V/k

V' = 18/2

V' = 9 V