Question

Many of the applications of capacitors depend on their ability to store energy.
1. In a charged capacitor energy is stored in the

• positively charged plate
• negatively charged plate
• electric field between the plates
• none of these 

2. Draw a graph showing the variation of charge stored in a capacitor with its potential. How will you calculate the energy stored in the capacitor using the above graph?

3. An electric flash lamp has 20 capacitors each of capacitance 5µF connected in parallel. The lamp is operated at 100 V. If the energy stored in the combination is completely radiated out in a single flash, how much energy will be radiated in a flash?

Answer 1

1. Electric field between the plates

2. 

Area under the straight line graph gives the energy stored in the capacitor.

3. Effective capacitance C = 20 × 5µF = 100µF, V = 100 v,

Energy stored E = \(\frac{1}{2}\)CV

E = \(\frac{1}{2}\times100\times10^{-6}\times100^2\) = 0.5 J