Question

A parallel plate capacitor is charged by connecting it to an ideal battery, the capacitor is then disconnected. Originally the energy stored in the capacitor is U∘. If the distance between the plates is doubled, then the new energy stored in the capacitor will be

Answer 1

Explanation:

When battery is disconnected charge on capacitor is constant

We know C=

d

ε

0

A

when d is doubled C

1

=

2d

ε

0

A

∴Now C

1

=

2

C

Q=C

1

V

1

⇒V

1

=2

C

Q

=2V

∴E

1

=

2

1

C

1

0

V

1

2

=

2

1

⋅

2

C

⋅4V

2

=CV

2

II) When battery is connected V does not change

Now C

2

=

2d

ε

0

A

∴E

2

=

2

1

C

2

V

2

2

=

2

1

⋅(

2

C

)V

2

=

4.

CV

2

∴

E

2

E

1

=

4

CV

2

CV

2

=