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 `lamda = 600 nm, ` power = 0.5kW, t = 60 ms
power `P = (nhc)/(lamda t) rArr n = (P lamda t)/(hc)`
` = 0.5 xx 10^3 xx (600 xx 10^(-9) xx 60 xx 10^(-3) )/(6.6 xx 10^(-34) xx 3 xx 10^8) `
` = 100 xx 10^18 = 10^20`