Question

The radiation having maximum wavelength is:
A.Ultraviolet rays
B.Radio waves
C.X rays
D.Infrared rays

Answer 1

As speed of light is constant thereby frequency of a radiation inversely proportional to its wavelength. The radiation with maximum wavelength has minimum frequency and vice versa.

Complete answer:
Electromagnetic radiation or light has dual nature namely wave nature and particle nature. Properties of light like interference and diffraction can only be explained if considered wave nature of light. On the other hand, properties of light like photoelectric effect and black body radiation can only be explained if considering the particle nature of light.
To understand the electromagnetic spectrum, we need to first understand some properties of electromagnetic radiation. Wave nature explains the wave associated with an accelerated charged particle is known as electromagnetic wave or electromagnetic radiation. In an electromagnetic radiation, electric field and magnetic field components have the same frequency, speed, wavelength, amplitude but only they oscillate in perpendicular planes. EM waves can travel through vacuum. Due to differences in terms of frequency or wavelength, we obtain a spectrum of electromagnetic radiation of different frequency and wavelength. These different regions of the electromagnetic spectrum are identified by different names.

Region of electromagnetic radiation	Frequency range	Wavelength range
$\gamma$ rays	$3 \times {10^{22}}{\text{ to }}3 \times {10^{18}}{\text{Hz}}$	${10^{ - 14}}{\text{ to }}{10^{ - 10}}{\text{m}}$
X ray	$5 \times {10^{19}}{\text{ to }}5 \times {10^{17}}{\text{Hz}}$	$6 \times {10^{ - 12}}{\text{ to }}{10^{ - 9}}{\text{m}}$
UV rays	$3 \times {10^{17}}{\text{ to }}5 \times {10^{19}}{\text{Hz}}$	$6 \times {10^{ - 10}}{\text{ to }}3.8 \times {10^{ - 7}}{\text{m}}$
Visible light	$8 \times {10^{14}}{\text{ to }}4 \times {10^{14}}{\text{Hz}}$	$3.8 \times {10^{ - 7}}{\text{ to }}7.8 \times {10^{ - 7}}{\text{m}}$
IR rays	$4 \times {10^{14}}{\text{ to }}3 \times {10^{11}}{\text{Hz}}$	$7.8 \times {10^{ - 7}}{\text{ to }}{10^{ - 3}}{\text{m}}$
Microwaves	$3 \times {10^{11}}{\text{ to }}{10^9}{\text{Hz}}$	${10^{ - 3}}{\text{ to }}0.3{\text{m}}$
Radio waves	${10^9}{\text{ to few Hz}}$	$0.3{\text{m to few Km}}$

As we can see, from moving $\gamma$ rays to radio waves; frequency decreases or wavelength increases. Thereby, decreasing order of frequency can be given by:
$\gamma {\text{rays}} > {\text{X ray}} > {\text{UV rays}} > {\text{visible light}} > {\text{IR rays}} > {\text{Microwaves}} > {\text{Radio waves}}$ and the order of increasing wavelength can be given by:
$\gamma {\text{rays}} < {\text{X rays}} < {\text{UV rays}} < {\text{Visible light}} < {\text{IR rays}} < {\text{Microwaves}} < {\text{Radio waves}}$ .

Thus, the correct option is B.
Note:
The electromagnetic waves consist of sinusoidal time varying electric and magnetic fields at right angles to each other as well as at right angles to the direction of propagation.