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Physics Olympiad 29

Posted: Mon Sep 28, 2009 8:41 pm
by noospace
http://www.princeton.edu/~jdpeters/docs ... piad99.pdf

I can't understand why the answer is E.

The velocity with which the ion enters the magnetic field is determined by

1/2 m v^2 = q V

ans so v is proportional to sqrt(q/m).

The radius of the arc in a magnetic field of strength B is proportional to (m * v) /q which is proportional to sqrt(m/q).

Since the oxygen is double the charge and quadruple the mass, we expect oxygen to have a radius which is increased by a factor of sqrt(2)

Re: Physics Olympiad 29

Posted: Mon Sep 28, 2009 9:00 pm
by blackcat007
noospace wrote:http://www.princeton.edu/~jdpeters/docs ... piad99.pdf

I can't understand why the answer is E.

The velocity with which the ion enters the magnetic field is determined by

1/2 m v^2 = q V

ans so v is proportional to sqrt(q/m).

The radius of the arc in a magnetic field of strength B is proportional to (m * v) /q which is proportional to sqrt(m/q).

Since the oxygen is double the charge and quadruple the mass, we expect oxygen to have a radius which is increased by a factor of sqrt(2)
yes even i have this same problem.. i think there is a mistake with the answer key

Re: Physics Olympiad 29

Posted: Mon Sep 28, 2009 11:57 pm
by noospace
Okay. That's a relief. I thought I was going crazy.