Department of Pre-University Education, KarnatakaPUC Karnataka Science Class 12
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The Relative Luminosity of Wavelength 600 Nm is 0.6. 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. - Physics


The relative luminosity of wavelength 600 nm is 0.6. 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.

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Relative luminosity = 0.6

Let P be the radiant flux of the source.

∴ Luminous flux = P × 685

Again, relative luminosity

`="Luminous flux of a source of given wavelength"/"Luminous flux of a source of 555nm of same power"`

`therefore0.6="Luminous flux of a source P watt"/(685P)`

`rArr685 xxPxx0.6=120xx685`

`rArr P=120/0.6=200W`

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

Concept: Light Process and Photometry
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HC Verma Class 11, 12 Concepts of Physics 1
Chapter 22 Photometry
Q 4 | Page 455
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