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  • A laser beam emits 2 watts of power at a wavelength of . Calculate the number of photo

A laser beam emits 2 watts of power at a wavelength of 500 \mathrm{~nm}. Calculate the number of photons emitted by the laser per second. (Take Planck's constant, h=6.626 \times 10^{-34} \mathrm{Js} and the speed of light, c=3 \times 10^8 \mathrm{~m} / \mathrm{s})

Option: 1

4.46 \times 10^{16}$ photons $/ \mathrm{s}


Option: 2

2.23 \times 10^{16}$ photons $/ \mathrm{s}


Option: 3

1.12 \times 10^{16}$ photons $/ \mathrm{s}


Option: 4

5.6 \times 10^{16}$ photons $/ \mathrm{s}


Answers (1)

best_answer

Given, power of the laser beam, P = 2 W and wavelength of the light emitted,

\lambda=500 \mathrm{~nm}=5 \times 10^{-7} \mathrm{~m}

Using the formula, 

n=\frac{P \lambda}{h c}

We can calculate the number of photons emitted per second by the laser beam as:

\begin{aligned} & \quad n=(2 \mathrm{~W})\left(5 \times 10^{-7} \mathrm{~m}\right) /\left(6.626 \times 10^{-34} \mathrm{Js} \times\right. \\ & \left.3 \times 10^8 \mathrm{~m} / \mathrm{s}\right) \\ & n=4.46 \times 10^{16} \mathrm{photons} / \mathrm{s} \end{aligned}

Therefore, option A is the correct answer.. 

 

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