If the frequency of an EM wave is $10$ MHz, then its wavelength is:
1. $30$ m
2. $300$ m
3. $3$ m
4. none of the above

The biological importance of the ozone layer is:

Which of the following has the minimum wavelength?
1. $X\text-$rays
2. Ultraviolet rays
3. $\gamma\text-$rays
4. Cosmic rays

What is the cause of “Greenhouse effect”?
1. Infra-red rays
2. Ultraviolet rays
3. $X\text-$rays
4. Radio waves

The velocity of electromagnetic waves is parallel to:

1. $\overrightarrow{\mathrm{B}}\times \overrightarrow{\mathrm{E}}$

2. $\overrightarrow{\mathrm{E}}\times \overrightarrow{\mathrm{B}}$

3. $\overrightarrow{\mathrm{E}}$

4. $\overrightarrow{\mathrm{B}}$

If $\lambda_{v}, \lambda_{x},$ and $\lambda_{m}$ represent the wavelengths of visible light, $x\text-$rays and microwaves respectively, then:
1. $\lambda_{m}>\lambda_{x}>\lambda_{v}$
2. $\lambda_{v}>\lambda_{m}>\lambda_{x }$
3. $\lambda_{v}>\lambda_{x}>\lambda_{m }$
4. $\lambda_{m}>\lambda_{v}>\lambda_{x}$