How to find the wavelength of a Photon with no mass?

[nukeman]

Homework Statement

Hey guys, So I just did a problem here: (its find wavelength of particle with mass)
https://www.physicsforums.com/showthread.php?t=596936

But I need to figure out how to find the wavelength of a Photon with no mass.

I know the formula I need is this: wavelength = c/f = hc/Energy

BUT... What would be a general question that would ask this? What variable would be given, as in the problem I listed above trying to find the wavelength of a particle with mass, I was given the speed, so I could then plug into equation.

What would I be given to ask to find the wavelength of a photo with no mass?

Much thanks!

Homework Equations

The Attempt at a Solution

 

[Redbelly98]

As far as I can think at the moment, a problem might provide any of the following types of information and ask you to find the wavelength:

• frequency
• photon energy
• photon momentum
• frequency and refractive index, if the photon is not traveling in vacuum
• frequency and speed, if the photon is not traveling in vacuum
• details of a diffraction or interference experiment