Q4 of 38 Page 455

The relative luminosity of wavelength 600 nm is 06. Find the radiant flux of 600 nm needed to produce the same brightness sensation as produced by 120 W of radiant flux at 555 nm.

Given,
Relative luminosity = 0.6
Let P be the radiant flux of the source.


∴ Luminous flux = P×685



Again,




⇒


⇒


So, 200 W radiant flux is needed to produce the same brightness sensation for 600 nm wavelength.


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2

A photographic plate records sufficiently intense lines when it is exposed for 12 s to a source of 10 W. How long should it be exposed to a 12 w source radiating the light of same colour to get equally intense lines?

 3

Using figure (22.1), find the relative luminosity of wavelength (A) 480 nm, (B) 520 nm (C) 580 nm and (D) 600 nm.

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The luminous flux of a monochromatic source of 1 w is 450 lumen. Find the relative luminosity at the wavelength emitted.

 6

A source emits light of wavelengths 555 nm and 600 nm. The radiant flux of the 555 nm part is 40 W and of the 600 nm part is 30 W. The relative luminosity at 600 nm is 06. Find (A) the total radiant flux, (B) the total luminous flux, (C) the luminous efficiency.