Question

Electrostatic energy of $3.5 \times {10^{ - 4}}$ J is stored in a capacitor at 700V. What is the charge on the capacitor?

Answer 1

Hint: As question says Electrostatic energy of $3.5 \times {10^{ - 4}}$ J and given voltage 700V. so, we have to apply voltage and energy related formulas, by putting these values we easily calculate the charge on the capacitor.

Formula used:
$Q = \dfrac{{2u}}{V}$

Complete Step by step solution:
We know that formula
$u = \dfrac{1}{2}QV$
u is the electrostatic energy.
Q is the charge.
V is the voltage.

Given values are $u = 3.5 \times {10^{ - 4}}$, V=700V, Q have to find.

From the formula we get.
$ \Rightarrow Q = \dfrac{{2u}}{V}$

Subtitue given values in the above equation
$ \Rightarrow Q = \dfrac{{2 \times 3.5 \times {{10}^{ - 4}}}}{{700}}$

Solve above equation we get
$\therefore Q = {10^{ - 6}}C$

Hence, charge on the capacitor is ${10^{ - 6}}C$.

Additional information:
$\bullet$ Capacitor is a device which stores electrical energy in the form of an electrical field.
$\bullet$ Commonly asked question in the viva is what is capacitance, we have to answer the effect of capacitor is known as capacitance.
$\bullet$ Electrostatic means electric charges at rest. Electrodynamics means motion of electric charges.
$\bullet$ Electrostatic may involve buildup of charge on the surface of material due to contact with other surfaces.
$\bullet$ Voltage is nothing but electric potential difference. The dimension of the voltage is ${\text{M}}{{\text{L}}^{\text{2}}}{{\text{T}}^{{\text{ - 3}}}}{{\text{I}}^{{\text{ - 1}}}}$ and its unit is volt which is denoted as V.
$\bullet$ Electric current is proportional to voltage and inversely proportional to resistance which is stated in a ohm's law.
$\bullet$ Resistance is measured in ohms, resistance means the measurement of opposition to current flow.

Note:
We know that here one faraday capacitor at a voltage of 1 volt stores one-coulomb is equivalent to $6.25 \times {10^{18}}$ electrons and a current of 1A shows rate of 1 coulomb each second, hence there is a capacitor of one faraday at 1 volt can store one ampere second electron.