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 = 6.62 × 10 − 34   J s )

Step-by-step solution

The energy of photon is given by E = h c λ . Power P is given as, P = E t = n h c λ t From the above equation, the number of photons is n = P λ t h c = 0.5 × 10 3 × 660 × 10 - 9 × 60 × 10 - 3 6.6 × 10 - 34 × 3 × 10 8 Hence, number of photons in the pulse are = 100 × 10 18 = 10 20 .