Question

The decreasing order of wavelength of infrared, microwave, ultraviolet and gamma rays is
(A) Microwaves, infrared, ultraviolet, gamma rays
(B) Infrared, microwaves, ultraviolet, gamma rays
(C) Ultraviolet, gamma rays, infrared, microwaves
(D) Microwaves, gamma rays, infrared, ultraviolet

Answer 1

For decreasing order of wavelength of infrared, microwave, ultraviolet and gamma rays, first we have to calculate the wavelength of these rays experimentally after then arrange them in decreasing order with the help of numeric data.
For calculating the wavelength of infrared, microwave, ultraviolet and gamma rays experimentally, we use following formula -
$\lambda = \dfrac{c}{f}$
Where
f $=$ frequency of wave
c $=$ speed of light
$\lambda =$ wavelength of wave

Complete step by step solution:
All 4 waves i.e., microwaves, infrared, ultraviolet and gamma rays are the part of electromagnetic wave and its wavelength experimentally given as
For microwaves wavelengths range is
$1mm - 25\mu m$ …..(1)
For infrared wavelengths range is
$25\mu m - 2.5\mu m$ …..(2)
For ultraviolet wavelengths range is
$400nm - 1\mu m$ …..(3)
For gamma wavelengths range is
$< {10^{ - 12}}m$ …..(4)
Therefore, the decreasing order wavelength is
Microwaves $>$ Infrared $>$ Ultraviolet $>$ gamma rays

So, option A is correct.

Note: The decreasing order of the wavelength for the given rays is opposite to the order of their frequencies because the frequency of the wave is inversely proportional to the wavelength $f \propto \dfrac{1}{\lambda }$
To order of frequency for the wave is Microwaves $>$ Infrared $>$ Ultraviolet $>$ gamma rays
Therefore, the decreasing order wavelength is
Microwaves $>$ Infrared $>$ Ultraviolet $>$ gamma rays