Question

Unit of energy density of electromagnetic wave is (A) \(\mathrm{Jm}^{-3}\) (B) \(\mathrm{Jm}^{-2}\) (C) \(\mathrm{wm}^{-2}\) (D) None of these

Short answer

The unit of energy density of an electromagnetic wave is: (A) \(\mathrm{Jm}^{-3}\).

Step-by-step solution

Option A: Jm⁻³

This unit represents Joules per cubic meter, which means energy per unit volume. This fits the definition of energy density. We can keep this option as a potential answer.

Option B: Jm⁻²

This unit represents Joules per square meter, which implies energy per unit area. However, the exercise asks for energy density, which is energy per unit volume, not per unit area. So, this option is incorrect.

Option C: wm⁻²

This unit may look a bit confusing at first, but it appears to be Watts per square meter (Wm⁻²). Watts is a unit of power, not energy, and again, the unit is per unit area instead of per unit volume. So, this option is incorrect.

Option D: None of these

Option A is suitable as the unit for energy density, so this "none of these" option is incorrect as there is a correct choice available among the given options. To conclude, the unit of energy density of an electromagnetic wave is: (A) \(\mathrm{Jm}^{-3}\)