A 50 watt bulb emits monochromatic red light of wavelength of 795 nm. The number of photons emitted per second by the bulb is x $\times$ 10²⁰. The value of x is __________. [Given : h = 6.63 $\times$ 10^$-$34 Js and c = 3.0 $\times$ 10⁸ ms^$-$1]

Energy of photon is given as $E = {{nhc} \over \lambda }$ .... (i)<br/><br/>where, E = energy of photon (50 W),<br/><br/>n = number of photon<br/><br/>h = Planck's constant (6.63 $\times$ 10^$-$34 Js)<br/><br/>c = speed of light (3 $\times$ 10⁸ m/s)<br/><br/>$\lambda$ = wavelength of light (795 $\times$ 10^$-$9 m)<br/><br/>E = 50W = 50 J = energy of photon<br/><br/>50 J = $${{n \times 6.63 \times {{10}^{ - 34}}Js \times 3 \times {{10}^8}m/s} \over {795 \times {{10}^{ - 9}}m}}$$<br/><br/>$\Rightarrow$ $$n = {{50 \times 795 \times {{10}^{ - 9}}} \over {6.63 \times {{10}^{ - 34}} \times 3 \times {{10}^8}}}$$<br/><br/>$= 1998.49 \times {10^{17}} = 1.998 \times {10^{20}}$<br/><br/>$\Rightarrow$ $\approx$ 2 $\times$ 10²⁰<br/><br/>$\therefore$ x = 2