### Video Transcript

What is the momentum of a 4.00-centimetre-wavelength photon?

We can call the wavelength of this photon đťś†. And we want to solve for its momentum, which weâ€™ll call đť‘ť. To begin, we can recall the relationship for the momentum of a photon. Photon momentum đť‘ť is equal to Planckâ€™s constant â„Ž over photon wavelength đťś†.

Planckâ€™s constant weâ€™ll treat in this problem as exactly 6.626 times 10 to the negative 34th joule seconds. So đť‘ť equals â„Ž over đťś†. And when we plug in for these two values, being careful to use units of metres in our expression for đťś† and calculate đť‘ť, we find that to three significant figures itâ€™s 1.66 times 10 to the negative 32 kilograms metres per second. Thatâ€™s the momentum this photon has.