A 200 W sodium street lamp emits yellow light of wavelength 0.6 μ m. Assuming it to be 25 % efficient in converting electrical energy to light, the number of photons of yellow light emitted per second is

Question

A 200 W sodium street lamp emits yellow light of wavelength 0.6 μ m. Assuming it to be 25 % efficient in converting electrical energy to light, the number of photons of yellow light emitted per second is (A) 1.5× 1020 (B) 6× 1018 (C) 62× 1020 (D) 3× 1019

Tardigrade Admin · Accepted Answer

Efficient power p=(N/t)× (h c/λ )=200× 0.25 (N/t)=50× (λ /h c) =(50 × 0.6 × 10- 6/6.6 × 10- 34 × 3 × 108) =1.5× 1020

Q. A $200 W$ sodium street lamp emits yellow light of wavelength $0.6 μ m .$ Assuming it to be $25%$ efficient in converting electrical energy to light, the number of photons of yellow light emitted per second is

$1.5 \times 1 0^{20}$

$6 \times 1 0^{18}$

$62 \times 1 0^{20}$

$3 \times 1 0^{19}$

Efficient power $p = \frac{N}{t} \times \frac{h c}{λ} = 200 \times 0.25$
$\frac{N}{t} = 50 \times \frac{λ}{h c}$
$= \frac{50 \times 0.6 \times 1 0 ^{- 6}}{6.6 \times 1 0 ^{- 34} \times 3 \times 1 0 ^{8}}$
$= 1.5 \times 1 0^{20}$

Q. A 200W sodium street lamp emits yellow light of wavelength 0.6μm. Assuming it to be 25% efficient in converting electrical energy to light, the number of photons of yellow light emitted per second is

1.5×1020

6×1018

62×1020

3×1019