Question

A parallel-plate air capacitor of capacitance Co is connected to a cell of emf E and then disconnected from it. A dielectric slab of
dielectric constant K, which can just fill the air gap of the capacitor, is now inserted in it. Which is incorrect?​

Answer 1

Answer:

C

f

=KC

i

Q

i

=C

i

V

U

i

=

2

1

C

i

V

2

U

f

=

2

1

C

f

Q

f

2

After the capacitor is disconnected from the battery, charge on the capacitor cannot change.

∴Q

f

=Q

i

∴U

f

=

2

1

C

f

Q

f

2

=

2

1

KC

i

C

i

2

V

2

ΔU=U

f

−U

i

=

2

1

KC

i

C

i

2

V

2

−

2

1

C

i

V

2

=

2

1

C

i

V

2

(

K

1

−1)=

2

1

CV

2

(

K

1

−1) since C

i

=C as given