A laser light of wavelength 660 nm is used to weld Retina detachment. If a laser pulse of width 60 ms and power 0.5 kW is used, the approximate number of photons in the pulse are (Take Planck's Constant, `h=6.62xx10^(-34)Js`)

Options

A. `10^20`
B. `10^18`
C. `10^22`
D. `10^19`

Answer

A

Explanation

Given that the power of the laser light, `P=0.5kW = 0.5 xx10^3W`
width of the laser pulse, `t= 60 ms =60xx10^(-3)s`
Wavelength of the laser light,
`lamda=660nm =660 xx10^(-9)m`
Let the number of photons in the pulse be n.
The energy of a photon is given by
`E=(hc)/lamda`
The power of the pulse is given by
`P=(nhc)/(lamdat)`
`impliesn=(Plamdat)/(hc)`
`n=0.5xx10^3xx(660xx10^(-9)xx60xx10^(-3))/(6.6xx10^(-34)xx3xx10^8)=10^(20)`