IIT JEE , AIEEE Forum - Physics , Modern Physics

rakshit

a photon of energy 10.2 eV collides inelasticallywith a stationary hydrogen atom(in ground state). after few micro second another photon of energy 15.0eV collides with same hydrogen atom .which of the following can be detected by a suitable detector?

ans -one photon of 10.2eV and an electron of energy 1.4 eV.

pearlypeeble

since the energy required for electron to jump from ground state to first excited state is 10.2 eV. as there is very less probability of electron getting all the energy( I don't say it can't be transferred but it may happen that elctron does not absorbs any energy and a photon of that amt. of energy may be released).
note that in this case it may also happen that electron jumps to the first excited level and no photon to be detected.
But it cannot be that atom absorbs the energy partially(considering Bohr's atomic model to be valid)
For second case , since the energy is sufficient for electron to jump to second excited state.(Although this jump to first excited state is having high probability but the transference of electron to second excited state is having very less probability).thus remaining energy is emitted in the form of photon having energy of 1.4 eV

bhupesh

Dear

I didnt understand why it should be an inellasttic collision and secondly if it is then conservation of momentum must also be satisfied which will prohibit any exitation of the hydrogen atoom as a part of the energy will be utilised in imaparting KE to the hydrogen atomm it self

nikhilwalani

i think so pearlypeeble is wrong in stating that the electron in second case will jump to the second level but it will come out as the energy is more than its ionisation energy.

bhupesh

Dear Rakshit
First let me tell you your question is very interesting secondly with or with out Bohr theory the photon atom collision can be understood to be elastic and inelastic can you think of situation when this is going to be inelastic ??? you know an electron's energy can have certain value only ( quantization ) what if the energy supplied by the photon is more or less than the accepted value of energy ( quantized level ) in this case the electron is not going to jump to the energy level since its not defined and we would say the collision to be inelastic

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