how many photons

Question

A laser is used in eye surgery to weld a detached retina back into place. The wavelength of the laser beam is 596 nm, while the power is 2.1 W. During surgery, the laser beam is turned on for 0.055 s. During this time, how many photons are emitted by the laser?

Answer 1

Hey Aly,

The main idea here is to find the energy of a single photon from this laser and then divide that into the total energy required during the procedure.

The energy of a photon is given by E = hf = hc/λ. Just remember to put your wavelength into meters first.

The total energy used during the procedure can be found with the general equation for power: P = E/t, or E = P*t.

Now just divide the total energy by the energy of one photon to find your answer.

Hope this helps,

Chris