Show that instantaneous energy density in electromagnetic wave is equally divided among electric and magnetic field.

Explanation

To show that the instantaneous energy density in an electromagnetic wave is equally divided between the electric field and the magnetic field, we can follow these steps:

### Step 1: Define the Energy Densities
The energy density \( U \) in an electromagnetic wave can be expressed as the sum of the energy densities due to the electric field \( U_e \) and the magnetic field \( U_m \):
\[ U = U_e + U_m \]
Where:
...