Physics GRE Discussion Forums

What could be the possible answer ?
Acco to me it should be option (B). But i am not sure about it....

Here's another vote for (b).

If it were an infinite mass atom then it would be (a). With a finite mass, some of the energy of the photon will become kinetic energy of the energized atom. This means you need a little extra energy hence (b).

To get the answer exactly, you can use the relation $$E^2 = (pc)^2 + (m_0c^2)^2,$$ and the fact that the momentum of the atom after the collision is the same as the momentum of the photon, to get $$(Mc^2 + fh)^2 = (fh)^2 + ((M + \Delta)c^2)^2,$$ and then solve for f.

kroner wrote:To get the answer exactly, you can use the relation $$E^2 = (pc)^2 + (m_0c^2)^2,$$ and the fact that the momentum of the atom after the collision is the same as the momentum of the photon, to get $$(Mc^2 + fh)^2 = (fh)^2 + ((M + \Delta)c^2)^2,$$ and then solve for f.

Solving for f looks too haaaaaaaaard.

-Riley

WhoaNonstop wrote:

kroner wrote:To get the answer exactly, you can use the relation $$E^2 = (pc)^2 + (m_0c^2)^2,$$ and the fact that the momentum of the atom after the collision is the same as the momentum of the photon, to get $$(Mc^2 + fh)^2 = (fh)^2 + ((M + \Delta)c^2)^2,$$ and then solve for f.

Solving for f looks too haaaaaaaaard.

-Riley

That's why Mathematica has the solve function. Just the other day I came across some really difficult algebra and had to have Mathematica break it down for me. How in the hell am I supposed to know how to solve x+2=4?

Thanks for the solution ..... please help me solve two more problems.........

Mind sharing where these problems are from?

Well these problems are from last year's entrance exam for PhD(physics) program at TIFR,india...