Refractive index for a material for infrared light is
[CPMT 1984]
Equal to that of ultraviolet light
Less than for ultraviolet light
Equal to that for red colour of light
Greater than that for ultraviolet light
The threshold wavelength for photoelectric emission from a material is 5200˙A. Photoelectrons will be emitted when this material is illuminated with monochromatic radiation from a
Give reason for the following :
(i) Infrared radiations are used for photography in fog.
(ii) Infrared radiations are used for signals during the war.
(iii) The photographic darkrooms are provided with the infrared lamps.
(iv) A rock salt prism is used instead of a glass prism to obtain the infrared spectrum.
(v) A quartz prism is required for obtaining the spectrum of the ultraviolet light.
(vi) Ultraviolet bulbs have a quartz envelope instead of glass.