Question

Two metal plates X and Y of the area ‘A’ are separated by a distance ‘d’, charged + and – respectively.

1. This arrangement is called………

2. The arrangement store energy in the………..(Magnetic field, Electric field, Electromagnetic field, Gravitational field)

3. Derive an expression for the energy stored in the arrangement.

4. When we increase separation between two plates by keeping V constant, what happens to total energy stored in the system.

Answer 1

1. Capacitor.

2. Electric field

3. If we supply a charge ‘dq’ to the capacitor, then work done can be written as,

dw = Vdq

dw = \(\frac{q}{c}\) dq (since v = \(\frac{q}{c}\) ) 

∴ Total work done to charge the capacitor (from ‘0’ to ‘Q’) is

4. When we increase the separation between two plates, capacitance (c) decreases. The energy in the capacitor U = \(\frac{1}{2}\) CV² When c decreases, the energy decreases (because V is constant).