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A laser light of wavelength 660 nm is us...

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`)

A

`10^(22)`

B

`10^(19)`

C

`10^(20)`

D

`10^(18)`

Text Solution

Verified by Experts

The correct Answer is:
C
The energy of photon is given by
`E=(hc)/(lambda)`
Power P is given as, `P=(E)/(t)=(nhc)/(lambdat)`
From the above equation, the number of photons is `n (P lambda t)/(hc)`
`=0.5xx10^(3)xx(660xx10^(-9)xx60xx10^(-3))/(6.6xx10^(-34)xx3xx10^(8))`
Hence, number of photons in the pulse are `=100xx10^(18)=10^(20)`
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