The energy of a photon is proportional to its frequency.

E = hf

The constant of proportionality is called the Planck constant. It has the symbol 'h' and is on your data sheet. It has a value of 6.63 x 10 ^-34 Js

Now, for all electromagnetic radiation the velocity is 'c' (the speed of light - again on your data sheet as 3.0 x 10⁸ m/s).

Combining this equation with the wave equation we have:

(always write it this way - learn to - it saves time!)

Try this question:

A 50W lamp radiates in the visible region of the spectrun (400 to 700 nm). Estimate the number of photons produces each second by the lamp.

Click here for the answer

Now, Einsein's equation E = mc² links mass and energy. Mass can be converted into energy and vice versa.

We can therefore find the mass equivalent of a photon and then work out its momentum!

E = hf = mc²

so,

m_photon = hf/c²

and as the momentum of the photon = mc

p_photon = hf/c

but

f = c/l

so p_photon = h/l