Question

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 is

Answer 1

Formula of power is given by
P = nhc/λt
Here n is the number of photons , h is plank's constant , c is the speed of light , λ is the wavelength and t is the time .
n = Pλt/hc
Here , P = 0.5kW = 500W
λ = 660 nm = 660 × 10⁻⁹ m
t = 60 ms = 60 × 10⁻³ sec = 0.06 sec
h = 6.6 × 10⁻³⁴ Js and c = 3 × 10⁸ m/s

Now, n = 500 × 660 × 10⁻⁹ × 0.06/6.6 × 10⁻³⁴ × 3 × 10⁸
= (500 × 100 × 0.06/3 ) × 10¹⁷
= 1000 × 10¹⁷
= 10²⁰

Hence, number of photons = 10²⁰

Answer 2

Answer:

Explanation:

we know ,no. of photons per second is equal to Power/area

so, n=N/t=P/E now see the entire part of the problem..i give the image