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NEET 2012
Exam
NEET
Year
2012
Subject
Physics
Chapter
Dual Nature of Matter

NEET 2012 · Physics · Dual Nature of Matter

A 200 ~W sodium street lamp emits yellow light of wavelength 0.6 μ...

A 200 W200 \mathrm{~W} sodium street lamp emits yellow light of wavelength 0.6μm0.6 \mu \mathrm{m}. Assuming it to be 25%25 \% efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is

Options

  1. A1.5×10201.5 \times 10^{20}
  2. B6×10186 \times 10^{18}
  3. C62×102062 \times 10^{20}
  4. D3×10193 \times 10^{19}

Correct answer

A. 1.5×10201.5 \times 10^{20}

Step-by-step solution

Efficient power P=Nt×hcλ=200×0.25P=\frac{N}{t} \times \frac{h c}{\lambda}=200 \times 0.25Nt=50×λhc=50×0.6×10−66.6×10−34×3×108=1.5×1020\begin{aligned} & \frac{N}{t} =50 \times \frac{\lambda}{h c} \\ & =\frac{50 \times 0.6 \times 10^{-6}}{6.6 \times 10^{-34} \times 3 \times 10^8} \\ & =1.5 \times 10^{20} \end{aligned}$$
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