The power output of a laser is measured by its wattage, the number of joules of energy it radiates per second (1 w = 1 j s-1). a 300-mw krypton laser produces a beam of red light with a wavelength of 676.4 nm (6.764×10-7 m). (a) calculate the energy carried by each photon. (b) calculate the number of photons emitted by the laser per second.

Explanation:

It is given that,

Wavelength of red light,

Power of the laser,

(a) The energy carried by each photon is given by :

(b) Let n is the number of photons emitted by the laser per second. It can be calculated as :

Hence, this is the required solution.    

you'd use the equation that establishes a relationship between  energy  and  wavelength, which looks like this

e=h⋅cλ, where

λ  - the wavelength of the photon; c  - the speed of light, usually given as  3⋅108m/s; h  -  planck's constant, equal to  6.626⋅10−34j s

plug the value you were given for the energy of the photon in the above equation to get the wavelength

e=h⋅cλ⇒λ=h⋅ce

λ=6.626⋅10−34js⋅3⋅108ms−1.257⋅10−24j=1.581⋅10−1m