The power of a red laser (λ = 630 nm) is 3.25 watts (abbreviated w, where 1 w = 1 j/s). how many photons per second does the laser emit?

The number of photons per second emitted by the laser is .

Energy of a single photon of the red light

The energy of a single photon of the red laser is calculated as follows;

Number of photons emitted by the laser

The number of photons per second emitted by the laser is calculated as follows;

Power of the laser = 3.25 W = 3.25 J/s

Thus, the number of photons per second emitted by the laser is .

Learn more about energy of emitted photons here: link

The energy delivered by the laser in 1 second is
In order to find how many photons correspond to this energy, we must calculate the energy of a single photon.
Calling h the Planck constant, c the speed of light and the wavelength of the light, the energy of a single photon is given by


So, the number of photons emitted by the laser in 1 second is equal to the total energy delivered by the laser divided by the energy of a single photon:
photons

Efficiency is an action of doing something. for example when you take a test. good efficiency means you did well but bad effeciency or no effiency means you did bad.