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i studied at school that an electron gains energy and gets excited by absorbing a photon.but this would increase its mass and the increase in the energy will result in ana increased frequency.frequncy being directly proportional to the velocity, velocity increases too. so in short there is an increase in the mass and velocity of the electron.but i think this would violate the law of conservation momentum. pls give an answer to this. Thanks in advance!

i studied at school that an electron gains energy and gets excited by absorbing a photon.but this would increase its mass and the increase in the energy will result in ana increased frequency.frequncy being directly proportional to the velocity, velocity increases too. so in short there is an increase in the mass and velocity of the electron.but i think this would violate the law of conservation momentum. pls give an answer to this.
Thanks in advance!

Grade:11

1 Answers

ali AskiitiansExpert-IIT
24 Points
12 years ago

Dear Athul R S,

Why you think, it violates conservation of momentum. In the phenomenon of photon absorption by electron no external agency is exerting force, hence obviously momentum will be conserved there.

Second thing photon is a packet of energy only. Its rest mass is zero.

Absorption of photon (energy) by electron in a matter increases its kinetic energy only. If total energy of electron exceeds a particular value constant for a given matter (work function), lector leave the surface of matter (called photoelectron). If not electron goes in excited state for

 10-8 s. Again come back to normal state by exciting photon of same energy.

In this way electron interact with photon.

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