Question

A $50$ watt bulb emits monochromatic red light of wavelength of $795nm$. The number of photons emitted per second by the bulb is $x\times 10^{20}$, The value of $x$ is _____.
[Given : $h=6.63\times 10^{-34}Js$ and $c-3.0\times 10^{8}m{s}^{-1}$ ]

Answer 1

Answer: 2

Total energy per sec. $=50J$
$50=\frac{n\times 6.63\times 10^{-34}\times 3\times 10^8}{795\times 10^{-9}}$
$n=1998.49\times 10^{17}$
$[n=$ no. of photons per second $]$
$=1.998\times 10^{20}$
$\simeq 2\times 10^{20}$
$=x\times 10^{20}$
$x=2$