Question

Calculate the number of photons emitted in 10 hours by 60 watt sodium lamp emitting radiation of wavelength 6000 angstrom.

Answer 1

Given , Power = 60W

time = 10 hours = 10 × 3600 sec = 3.6 × 10⁴ sec

We know, Energy = Power × time

so, Energy = 60W × 3.6 × 10⁴ sec = 21.6 × 10⁵J

Energy = 2.16 × 10⁶J

Now, A/C planks theory,

Energy of one photon = hc/λ ,

Here h is plank's constant and λ is wavelength of light emitted by sodium lamp.

you forgot to write wavelength of photon .

it is given λ = 5893 A° = 5.893 × 10⁻⁷ m

Now, Energy of one photon = 6.63 × 10⁻³⁴ × 3 × 10⁸/5.893 × 10⁻⁷

= 19.89/5.893 × 10⁻¹⁹ J

Now, number of photons = energy /energy of one photon

= 2.16 × 10⁶/{19.89/5.983 × 10⁻¹⁹}

= {2.16 × 5.893/19.89 }× 10²⁵

= 0.64 × 10²⁵

number of photons = 6.4 × 10²⁴