Question

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.

Answer 1

See below

Explanation:

Here's what your textbook did:

`E= (hc)/lamda`

`E=((6.63*10^(-34)Js)(3*10^8 m/s))/ (0.1 m)= 1.989*10^(-24) J or kgm^2/s^2`

`E=mc^2`

`E/c^2= m`

`m= (1.989 *10^-24 J)/ (3*10^8 m/s)^2`

`m =2.21*10^(-41) kg`

And you're right about a photon being maseless, this is an incorrect application of `E=Deltamc^2`

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

Answer 2

"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!