Answer the following: (a) Name the EM waves which are used for the treatment of certain forms of cancer. Write their frequency range. (b) Why is the ozone layer on top of the stratosphere crucial for human survival?

(a) Gamma (γ) rays are used for the treatment of certain forms of cancer. Their frequency range is 3×1019 Hz to 5×1024 Hz
(b) The thin ozone layer on top of the stratosphere absorbs most of the harmful ultraviolet rays coming from the sun towards the Earth. They include UVA, UVB and UVC radiations, which can destroy the life system on the Earth. Hence, this layer is crucial for human survival.
(c) Momentum transferred = Energy/Speed of light = hν/c = 10-26 (for ν = 1020 Hz) Thus, the amount of momentum transferred by the EM waves incident on the surface is very small.