Question

A capacitor (without dielectric) is discharging through a resistor. At same instant a dielectric is inserted between the plates, then-

• A. Just after the insertion of the dielectric, current will increase
• B. Just after the insertion of the dielectric charge on capacitor will increase
• C. Just after the insertion of the dielectric, energy stored in the capacitor will increase
• D. After the insertion of the dielectric, time constant will increase

Answer 1

Answer: (D)

After the insertion of the dielectric, time constant will increase

Answer 2

Let the capacitance before insertion of dielectric be C and the resistance be R.

\ q = q₀ $e ^ { \frac { \mathrm { t } } { \mathrm { RC } } }$ and i =

Just after insertion of dielectric the capacitance increases.

The charge just after insertion of dielectric remains same, but the current decreases Ž (1) and (2) are false.

The energy stored in capacitor is, hence energy decreases.

Ž (3) is false.

The time constant is RC and hence increases.

Ž (4) is true.