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NEET-XII-Physics

22: Photometry

with Solutions - page 3
Qstn# iv-6-a Prvs-QstnNext-Qstn
  • #6-a
    the total radiant flux, (b) the total luminous flux, (c) the luminous efficiency.
    Ans : Total radiant flux = radiant flux of 555 nm part of light + radiant flux of 600 nm part of light
    = 40 W + 30 W = 70 W (b) Total luminous flux = luminous flux of 555 nm part of light + luminous flux of 600 nm part of light
    = 1 × 40 × 685 + 0.6 × 30 × 685
    = 39730 lumen (c) `` \,\mathrm{\,Luminous\,}\,\mathrm{\,efficiency\,}=\frac{\,\mathrm{\,Total\,}\,\mathrm{\,luminous\,}\,\mathrm{\,flux\,}}{\,\mathrm{\,Total\,}\,\mathrm{\,radiant\,}\,\mathrm{\,flux\,}}``
    `` =\frac{39730}{70}=567.6\,\mathrm{\,lumen\,}/\,\mathrm{\,W\,}``
    So, the luminous efficiency is 568 lumen/W.
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  • #6-b
    the total luminous flux,
    Ans : Total luminous flux = luminous flux of 555 nm part of light + luminous flux of 600 nm part of light
    = 1 × 40 × 685 + 0.6 × 30 × 685
    = 39730 lumen
  • #6-c
    the luminous efficiency.
    Ans : `` \,\mathrm{\,Luminous\,}\,\mathrm{\,efficiency\,}=\frac{\,\mathrm{\,Total\,}\,\mathrm{\,luminous\,}\,\mathrm{\,flux\,}}{\,\mathrm{\,Total\,}\,\mathrm{\,radiant\,}\,\mathrm{\,flux\,}}``
    `` =\frac{39730}{70}=567.6\,\mathrm{\,lumen\,}/\,\mathrm{\,W\,}``
    So, the luminous efficiency is 568 lumen/W.
    Page No 455: