question_answer 7)

A 100 watt bulb emits monochromatic light of wavelength 400 nm. Calculate the number of photons emitted per second by the bulb.

Answer:

A 100 watt bulb will emit 100 J energy per second. Let \[x\] photons are emitted per second from the bulb. \[\therefore \] \[E=x\times h\frac{c}{\lambda }\] Given: \[E=100J\] \[h=6.626\times {{10}^{-34}}Js\] \[c=3\times {{10}^{8}}m\,{{\sec }^{-1}}\] \[\lambda =400\times \times {{10}^{-9}}m\] Putting these values in Eqn. (i) we get \[100=x\times \frac{6.626\times {{10}^{-34}}\times 3\times {{10}^{8}}}{400\times {{10}^{-9}}}\] \[x=\frac{100\times 400\times {{10}^{-9}}}{6.626\times {{10}^{-34}}\times 3\times {{10}^{8}}}\]photons \[=2.012\times {{10}^{20}}\]photons