Question

A condenser is charged and then battery is removed. A dielectric plate is put between the plates of condenser, then correct statement is

• A. Q is constant, V and U decrease
• B. Q is constant, V increases U decreases
• C. Q increases, V decreases U increases
• D. Q, V and U increase

Answer 1

Answer: (A)

Q is constant, V and U decrease

When a condenser is changed and the battery is removed the charge present on condenser remains same.
electric field is given by $\frac{\sigma }{{ϵ}_0}$
Now when dielectric plate is placed between $C=\frac{K{ϵ}_{0}A}{d}$ , C increases
We know $Q=C.V$
$V=\frac{Q}{C}$
as C increases with addition of dielectric V decreases
$\therefore$ As V decreases U decreases