If $E$ and $H$ represent the intensity of the electric field and the magnetising field respectively,then the unit of $E/H$ will be:

The velocity of electromagnetic waves is parallel to which of the following?

The electric field of a plane electromagnetic wave is given by: $E_y = 69 \sin[0.6 \times 10^3 x - 1.8 \times 10^{11} t] \text{ V/m}$. The expression for the magnetic field associated with this electromagnetic wave is . . . . . . $T$.

The electric field of a plane electromagnetic wave of wave number $k$ and angular frequency $\omega$ is given by $\vec{E} = E_0(\hat{i} + \hat{j}) \sin(kz - \omega t)$. Which of the following gives the direction of the associated magnetic field $\vec{B}$?

The equation of a light wave,normally incident on a surface,is given by $B = (100 \text{ nT}) \sin(2\pi(10^{15}t - (3 \times 10^{-7})x) + \frac{\pi}{6})$. Find the intensity of light on that surface in $W/m^2$.

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?