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11.Dual Nature of Radiation and matter
medium
A $200\, W$ sodium street lamp emits yellow light of wavelength $0.6\, \mu \,m$. Assuming it to be $50\%$ efficient in converting electrical energy to light, the number of photon of yellow light it emits per second is
A
$62 \times 10^{20}$
B
$3 \times 10^{20}$
C
$1.5 \times 10^{20}$
D
$6 \times 10^{18}$
Solution
Effective power $=\frac{50}{100} \times 200 \mathrm{\,W}=100 \mathrm{\,W}$
now, $100=n h v=\frac{\text { nhc }}{\lambda}$
$\mathrm{n}=\frac{\lambda \times 100}{\mathrm{hc}}=\frac{0.6 \times 10^{-6} \times 100}{20 \times 10^{-26}}=3 \times 10^{20}$
Standard 12
Physics
