Question

Which of the following represents an infrared wavelength?
A) ${10^{ - 4}}$ cm
B) ${10^{ - 5}}$ cm
C) ${10^{ - 6}}$ cm
D) ${10^{ - 7}}$ cm

Answer 1

Hint:Infrared radiations are electromagnetic radiations and thus is a part of the electromagnetic spectrum where all the radiations (electromagnetic) are distributed according to frequency and wavelength. The wavelength table of the electromagnetic spectrum can be used to identify which of the given options represents an infrared wavelength.
We need to carry out the conversions as all the options are given in cm.

Complete step by step answer:Electromagnetic spectrum is the range of all electromagnetic radiations and these radiations are distributed according to frequency and wavelength.
Infrared radiation is invisible to the eyes as these are beyond the red end of the visible spectrum.

Wavelength table of electromagnetic spectrum:

From the table it can be observed the range of Infrared radiations is:
700 nm to 1 mm
Converting this range into cm:
$700 \times {10^{ - 7}} = 7 \times {10^{ - 5}}cm$
$1 \times {10^{ - 1}} = 0.1cm({10^{ - 1}})$
Range in cm = $7 \times {10^{ - 5}}$ cm - ${10^{ - 1}}$
The only option falling under this range is ${10^{ - 4}}$ cm (Rest all does not fall into this range; either have lower or higher values)
Checking on number line:
From here, we can see that ${10^{ - 4}}$ satisfies this range but ${10^{ - 5}}$ cm, ${10^{ - 6}}$ cm, ${10^{ - 7}}$ cm does not.
Therefore, the correct answer is option A) ${10^{ - 4}}$ cm.

Note:Infrared radiations cannot be seen (as it is beyond visible rays wavelength) but can be felt due to its warmth.
It can be classified as near, middle and far depending upon its distance with respect to the visible spectrum.