Photon Question-Energy Quantization Question-

[quickclick330]

Photon Question-Energy Quantization Question---please help!

This is a somewhat simple question I'm just unsure what relations to use. I found an equation relating number of protons to power and frequency but I'm not sure how to apply it to this case.

EQUATION?

Power = energy per unit time
= (energy per photon) * (photon per unit time)
= (h*f) * (photons per unit time)

*where*
Power = wattage
h = Planck's constant
f = frequency.


QUESTION
A certain laser outputs pure red light (photon energy 1.8 eV) with power 550 milliwatts (0.55 watts). How many photons per second does this laser emit?
photons/s

-Thanks!

 

[Doc Al]

Looks like you have the correct relations. Just be sure to convert everything to standard units: eV to Joules, mW to Watts.

 

[ogb p]

Great question! To find the number of photons emitted per second by the laser, we can use the equation you mentioned:

Power = (h*f) * (photons per unit time)

We know the power (0.55 watts) and the photon energy (1.8 eV), so we can rearrange the equation to solve for the number of photons per second:

(photons per unit time) = Power / (h*f)

Substituting in the values, we get:

(photons per unit time) = 0.55 watts / (6.63 x 10^-34 J*s * (1.8 eV / 1 photon))

= 0.55 watts / (1.188 x 10^-19 J/photon)

= 4.63 x 10^18 photons/second

Therefore, the laser emits 4.63 x 10^18 photons per second. I hope this helps!