**Question 2.11: A 25-watt bulb emits monochromatic yellow light of wavelength of 0.57µm. Calculate the rate of emission of quanta per second.**

**Question 2.11: A 25-watt bulb emits monochromatic yellow light of wavelength of 0.57µm. Calculate the rate of emission of quanta per second.**

**Answer 2.11:** Power of bulb, P = 25 Watt = 25 Js^{–1}

The energy of one photon, E = hν = hc/Λ

Substituting the values of h, c, and Λ in the above relation

E = (6.626 × 10^{-34}) (3 × 10^{8})/0.57 × 10^{-6}

E = 34.87 × 10^{–20} J

Rate of emission of quanta per second = Power/ Energy

= 25 Js^{-1}/34.87 × 10^{–20} J = 7.169 × 10^{19} s^{-1}

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