A capacitor charged from a 100 V d.c supply is found to have charge of \( 20\,\mu\mathrm{C} \). How much energy is stored in it?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → \( 1 \times 10^{-3}\,\mathrm{J} \)
The energy stored in a charged capacitor is half the product of its charge and the potential difference across it.
\( \displaystyle U = \frac{1}{2}\,Q\,V \)
\( Q = 20\,\mu\mathrm{C} = 20\times10^{-6}\,\mathrm{C} \)
\( V = 100\,\mathrm{V} \)
\( \displaystyle U = \frac{1}{2} \times 20\times10^{-6} \times 100 = 1\times10^{-3}\,\mathrm{J} \)