NEET-XII-Physics
42: Photoelectric Effect and Wave Particle Duality
- #4Calculate the number of photons emitted per second by a 10 W sodium vapour lamp. Assume that 60% of the consumed energy is converted into light. Wavelength of sodium light = 590 nmAns : Given:
Power of the sodium vapour lamp, P = 10 W
Wavelength of sodium light, `` \lambda `` = 590 nm
Electric energy consumed by the bulb in one second = 10 J
Amount of energy converted into light = 60 %
∴ Energy converted into light = `` \frac{60}{100}\times 10=6\,\mathrm{\,J\,}``
Energy needed to emit a photon from the sodium atom,
`` E\text{'}=\frac{hc}{\lambda }``
`` E\text{'}=\frac{6.63\times {10}^{-34}\times 3\times {10}^{8}}{590\times {10}^{-9}}``
`` E\text{'}=\frac{6.63\times 3}{590}\times {10}^{-17}\,\mathrm{\,J\,}``
Number of photons emitted,
`` n=\frac{6}{{\displaystyle \frac{6.63\times 3}{590}}\times {10}^{-17}}``
`` n=\frac{6\times 590}{6.63\times 3}\times {10}^{17}``
n = 1.77 × 1019
Page No 365: