Question

Unit of energy density of electromagnetic wave is:

• A. $J{m}^{-3}$
• B. $J{m}^{-2}$
• C. $W{m}^{-2}$
• D. None of these

Answer 1

The correct option is A

$J{m}^{-3}$

Explanation of correct option

Option(A)-

Energy density:

1. It could be defined as the amount of energy stored in a system per unit volume. It is expressed as the ratio of the energy of a given system and its total volume.
2. Mathematically the energy density of a given system is expressed as, $Energydensity=\frac{Energy}{Volume}$.
3. The SI unit of energy is Joules $J$ and the SI unit of volume is meter-cube $m^3$. So, the unit of energy density is $J/m^3$.
4. Hence, the unit of the energy density of electromagnetic wave is $J/m^3$.

Explanation of incorrect options

Option(B)-

The volume of a 3D solid is calculated by multiplying length, breadth and height, therefore, $m^{-3}$and not $m^{-2}$

Option(C)-

Energy is measured in Joules($J$) and not weber (W)

Option(D)-

None of these cannot be the right option since option A is.correct.

Hence, option A is correct