Question

How many photons are emitted by a laser source $5\times {10}^{-3}W$ operating at $632.2nm$ in $2s$?

• A. $3.2\times {10}^{16}$
• B. $1.6\times {10}^{16}$
• C. $4\times {10}^{16}$
• D. None of these

Answer 1

The correct option is A

$3.2\times {10}^{16}$

Step 1: Given data

Power of laser source = $5\times {10}^{-3}W$

Operation time for laser = $2seconds$

Wavelength = $632.2nm$

Wavelength $=632.2x{10}^{-9}m$

Step 2: Formula used

The energy of the photon wavelength,$E_p=\frac{hc}{\lambda }$, here$h$ plank constant,$C$ the speed of light and $\lambda$ is the wavelength.

The number of photons$n=\frac{E_L}{E_p}$, here$E_L$ the energy released by the laser, $E_P$ the energy of one photon.

Step 3: Calculation of energy

The energy released by the laser source in $2sec$

$E_L=Powerxtime$

$E_L$$=5\times {10}^{-3}x2$

$E_L$$=10x{10}^{-3}$

$E_L$$={10}^{-2}Joule$

The energy of one photon with wavelength, $\lambda =632.2x{10}^{-9}m$

$E_p=\frac{hc}{\lambda }$

$E_p=3.13x{10}^{-19}$

Step 4: Calculation of number of the photon

Number of emitted photons in $2sec$

$n=\frac{E_L}{E_p}$

$n=\frac{{10}^{-2}}{3.13x{10}^{-19}}$

$n=3.2x{10}^{16}$

Hence, the correct option is (A).