$A$ beam of light travelling along the $X$-axis is described by the electric field $E_{y} = 900 \sin \omega(t - x/c)$. The ratio of the electric force to the magnetic force on a charge $q$ moving along the $Y$-axis with a speed of $3 \times 10^{7} \, m/s$ will be:
[Given: speed of light $c = 3 \times 10^{8} \, m/s$]

Answer the following questions:
$(a)$ Long distance radio broadcasts use short-wave bands. Why?
$(b)$ It is necessary to use satellites for long distance $TV$ transmission. Why?
$(c)$ Optical and radio telescopes are built on the ground but $X$-ray astronomy is possible only from satellites orbiting the earth. Why?
$(d)$ The small ozone layer on top of the stratosphere is crucial for human survival. Why?
$(e)$ If the earth did not have an atmosphere,would its average surface temperature be higher or lower than what it is now?
$(f)$ Some scientists have predicted that a global nuclear war on the earth would be followed by a severe 'nuclear winter' with a devastating effect on life on earth. What might be the basis of this prediction?

The speed of an electromagnetic wave in a medium (whose dielectric constant is $2.25$ and relative permeability is $4$) is equal to .......... $\times 10^8 \, m/s$.

$A$ point source of $100\,W$ emits light with $5\%$ efficiency. At a distance of $5\,m$ from the source,the intensity produced by the electric field component is:

The energy density associated with the electric field $\overrightarrow{E}$ and magnetic field $\overrightarrow{B}$ of an electromagnetic wave in free space is given by ($\epsilon_0$ - permittivity of free space,$\mu_0$ - permeability of free space):

Show that the radiation pressure exerted by an $EM$ wave of intensity $I$ on a surface kept in vacuum is $\frac{I}{c}$.