How is it possible that,photon doesn't have mass but it have momentum??

1 Answer
Phillip E. · Mark C.
Dec 17, 2017

Newton associated momentum with mass, but relativity changed it all.

Explanation:

Einstein's famous equation relating energy #E#, mass #m# and the speed of light #c#, has a hidden detail. The mass term increases as velocity increases.

#E=mc^2#

It can be written as:

#E^2=(m_0c^2)^2 +p^2c^2#

Where #m_0# is rest mass and #p# is momentum.

In the case of a photon it has no mass so #m_0=0#.

So, #E=pc#. A photon has energy which can be calculated from its frequency #nu# and Planck's constant #h#.

#E=h nu#

So as a photon has energy it also has momentum:

#p=(h nu)/c#

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