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**1.**Is binding energy equivalent to work (W)?

**2.**A He-Ne gas laser produces monochromatic red ligth with a wavelength of 6.3 x 10

^{-7}. If the beam is reflected normally from a mirror, what is the change in momentum of each photon on reflection?

I am particularly confused about this question. I used delta p = m(v - u) where v was the speed of light but it didn't result in the correct answer. Could anyone please give me a hint?

I also couldn't figure out what the mass of a photon was so I used the mass of an electron which I am sure is wrong.