# A photon of wavelength 100mm acts as a mass of? My text book gives the answer 2.21×10^-41. but a photon can't have mass because when an object travels with speed of light it's mass becomes infinite.

##### 2 Answers

Aug 5, 2018

#### Answer:

See below

#### Explanation:

Here's what your textbook did:

And you're right about a photon being maseless, this is an incorrect application of

Check this link out for more info on what the formula can be used for:

https://socratic.org/questions/can-you-thoroughly-describe-sigmund-freud-s-contributions-to-psychology?source=search

Aug 5, 2018

"a photon can't have mass because when an object travels with speed of light it's mass becomes infinite"

None of that makes any sense

EG:

- A photon is said to have zero rest-mass, as in, in its own reference frame it is massless.

So how do you reason that it can gain infinite mass? You are grossing up from zero!