JEE Physics 2025 Question with Solution

Given: The expression is $\sqrt{\frac{2I}{\epsilon_0 c}}$.

Find: The unit of the given expression.

For an electromagnetic wave, the intensity is

Substituting this into the given expression,

Hence,

The unit of electric field $E$ is $\text{N/C}$, equivalently $\text{N C}^{-1}$.

Therefore, the unit of the given expression is $\text{N C}^{-1}$. The correct option is D.

Given: $I$ is intensity, $\epsilon_0$ is permittivity of free space, and $c$ is the speed of light.

Find: The unit of $\sqrt{\frac{2I}{\epsilon_0 c}}$.

Using the units:

• $I$ has unit $\text{W/m}^2$
• $\epsilon_0$ has unit $\text{F/m}$
• $c$ has unit $\text{m/s}$

From electromagnetic wave theory, the expression corresponds to the electric field magnitude. Therefore its SI unit must be the unit of electric field.

So the required unit is $\text{N C}^{-1}$.

The solution also concludes that the correct option is D.