5(iii)
(a) Infrared radiations are used in warfare. Explain with reason, why.
(b) A ray of light is incident at 45° on an equilateral prism in the diagram below.
- (a)Name the phenomenon exhibited by the ray of light when it enters and emerges out of the prism.
- (b)State the cause of the above phenomenon mentioned by you.
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(a) Infrared radiations are used for signals during war because they are not visible and they are not absorbed much in the medium.
(b)
- Dispersion.
- The cause of dispersion of white light is the change in speed of light with wavelength.
When white light passes through a glass prism, its constituent colours (red, orange, yellow, green, blue, indigo, violet) travel with different speeds in the prism because each colour has different wavelength. This causes the dispersion of light.