How many photons are emitted per second by a 5 m W laser source operating at 632.8nm?

Explanation

The energy of each photon is
` E = (hc/lambda)`
` = ((6.63 xx (10^-34)J s) xx (3 xx (10^8)m (s^-1))/ (632.8 xx (10^-9)m))`
` = (3.14 xx (10^-9)m).`
The energy of the laser emitted per second is
` (5 xx (10^-3)J). Thus the number of photons emitted per`
second
` (5 xx (10^-3)J/ 3.14 xx (10^-19)J) = 1.6 xx (10^16).