The electromagnetic waves of wavelength in the range of 8000\(\overset{\circ }{\mathop{A}}\,\) to 10000000\(\overset{\circ }{\mathop{A}}\,\) are known as infrared radiations

Detection:

When a thermometer with a blackened bulb is moved from the violet end of the spectrum to the red end, a very sluggish rise in temperature is detected, but when it is moved beyond the red extreme, a rapid rise in temperature is observed. It means that there are certain radiations in the spectrum beyond the red extreme that produce a high heating effect but are not visible. Infrared radiations are the name for these types of radiations.

Because infrared radiation is not visible and does not absorb well in the medium, it is utilised as a signal during wartime.