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

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

Power of the bulb, $P = 25 Watt = 25\, Js^{-1}$

Energy (E) of one photon= $h\nu =\frac{hc}{\nu}$

Substituting these values in the expression for E:

$E=\frac{(6.626\times 10^{-34})(3\times 10^{8})}{(0.57\times 10^{-6})}$

$=34.87\times 10^{-20}\, J$

$E= 34.87\times 10^{-20}\, J$

Thus, the rate of discharge of quanta (per second) = $E=\frac{25}{34.87\times 10^{-20}}$

= $7.169\times 10^{19}\, s^{-1}$

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