MCQ
A $50\, watt$ bulb emits monochromatic red light of wavelength of $795\, \mathrm{~nm}$. The number of photons emitted per second by the bulb is $\mathrm{x} \times 10^{20}$. The value of $\mathrm{x}$ is ...... .

$\left[\right.$ Given $: \mathrm{h}=6.63 \times 10^{-34} \,\mathrm{Js}$ and $\left.\mathrm{c}=3.0 \times 10^{8} \,\mathrm{~ms}^{-1}\right]$

  • A
    $1$
  • B
    $4$
  • $2$
  • D
    $3$

Answer

Correct option: C.
$2$
c
Total energy per sec. $=50\, \mathrm{~J}$

$50=\frac{\mathrm{n} \times 6.63 \times 10^{-34} \times 3 \times 10^{8}}{795 \times 10^{-9}}$

$\mathrm{n}=1998.49 \times 10^{17}[\mathrm{n}=\mathrm{no} .$ of photons per second $]$

$=1.998 \times 10^{20}$

$\simeq 2 \times 10^{20}$

$=\mathrm{x} \times 10^{20}$

$\mathrm{x}=2$

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