What are ultra violet radiations? How are they detected? State one use of these radiations.

The electromagnetic radiations of wavelength λ = 100 Å to 4000 Å are called the ultraviolet radiations.

For the detection of ultra violet radiations —

If silver chloride solution is exposed to the electromagnetic waves starting from the red to the violet end and then beyond it, it is observed that from the red end to the violet end, the solution remains almost unaffected.

But just beyond the violet end, the solution first turns violet and then finally it becomes dark brown (or black).

It shows that there exists certain radiations beyond the violet extreme of the visible part, which are chemically more active than the visible light. These radiations are called the ultra violet radiations ( or actinic rays).

Ultraviolet radiations are used for sterilising air, surgical equipment, etc.