$A$ lamp emits monochromatic green light uniformly in all directions. The lamp is $3\%$ efficient in converting electrical power to electromagnetic waves and consumes $100\,W$ of power. The amplitude of the electric field associated with the electromagnetic radiation at a distance of $5\,m$ from the lamp will be nearly.......$V/m$

The peak value of the magnetic field of an electromagnetic wave moving in a magnetic field is $20 \, nT$. The peak value of the electric field intensity is ..... $V/m$.

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?

Why does a microwave oven heat up a food item containing water molecules most efficiently?

To heat the food containing water,the frequency of the microwaves used in a microwave oven is

Radio waves and visible light in vacuum have