Question

Calculate the rate of emission of quanta per second, when a $25watt$ bulb emits monochromatic yellow light of wavelength $ \, 0.57\mu m$ .

• A. $7.17 \, \times \, 10^{29} \, s^{- 1}$
• B. $ \, 7.17 \, \times \, 10^{11} \, s^{- 1}$
• C. $ \, 7.17 \, \times \, 10^{9} \, s^{- 1}$
• D. $ \, 7.17 \, \times \, 10^{19} \, s^{- 1}$

Answer 1

Answer: (D)

$\frac{E}{photon}=\frac{h c}{\lambda }=\frac{6.625 \times 10^{- 34} \times 3.0 \times 10^{8}}{0.57 \times 10^{- 6}}=34.86 \, \times \, 10^{- 20} \, J$ .
$Watt=No.ofphotons\frac{e m i t t e d}{s e c .}\times \frac{E}{p h o t o n}\left(W a t t = 25 J s^{- 1}\right)$ .
$25=No. \, of \, photons \, \times \, 34.86 \, \times \, 10^{- 20}$
$\therefore $ No. of photons emitted
$=\frac{25}{34.86 \times 10^{- 20}}=7.17 \, \times \, 10^{19}s^{- 1}$