For an electromagnetic wave travelling in free space,the relation between average energy densities due to electric $(U_{e})$ and magnetic $(U_{m})$ fields is

About $20 \%$ of the power of a $100 \ W$ bulb is converted to visible radiation. Assuming that the radiation is emitted isotropically and neglecting reflection,the average intensity of visible radiation at a distance of $5 \ m$ is $\frac{\alpha}{25 \pi} \ W/m^2$. The value of $\alpha$ is

$A$ plane electromagnetic wave is incident on a plane surface of area $A$ normally,and is perfectly reflected. If energy $E$ strikes the surface in time $t$,then the average pressure exerted on the surface is ($c=$ speed of light).

For a plane electromagnetic wave,the magnetic field at a point $x$ and time $t$ is $\overrightarrow{ B }( x , t ) = [1.2 \times 10^{-7} \sin (0.5 \times 10^{3} x + 1.5 \times 10^{11} t) \hat{ k }] \text{ T}$. The instantaneous electric field $\overrightarrow{ E }$ corresponding to $\overrightarrow{ B }$ is: (speed of light $c = 3 \times 10^{8} \text{ m/s}$)

The electric field of a plane electromagnetic wave is given by $\vec E = E_0 \hat i \cos(kz) \cos(\omega t)$. The corresponding magnetic field $\vec B$ is then given by:

The average value of electric energy density in an electromagnetic wave is: