Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-l] Electron vs. Alpha particle...



Since the charges are of opposite sign, is minimum approach a viable concept here?

Bob at pC

________________________________________
From: phys-l-bounces@carnot.physics.buffalo.edu [phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of ludwik kowalski [kowalskil@mail.montclair.edu]
Sent: Wednesday, January 12, 2011 5:55 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] Electron vs. Alpha particle...

You are right that a single collision would have a negligible effect
of an alpha particle. But why are alpha particles slowed down, as they
travel through air, wood, aluminum, etc.? Becaus of zilions of such
"collisions."

In the context of the "point particles" model the distance of minimum
approach can always be calculated. It depends on the initial energy of
the relative motion, and on the impact parameter. For a head-on
collision the impact parameter is zero, but the distance of the
minimum approach is not zero. So match for the classical model
approximation of reality. That model has been used very successfully
to calculate ranges of alpha particles, using an adjustable parameter
(which takes under consideration non-classical effects).

Ludwik
======================================


On Jan 12, 2011, at 5:38 PM, Jeff Loats wrote:

Hi all,

In discussing Rutherford scattering I ask students to use the simple
case of
an alpha particle colliding head on with an electron at rest. The
idea is to
use conservation of energy and momentum to show that in a classical
"billiard ball" model, the alpha particle can ignore electrons in
its path
to a good approximation.

This term a curious student asked some great questions about what
would
happen when such a collision took place.

This exceeded my knowledge a bit, so I thought I would ask here.

What would happen if an alpha particle was fired head-on at an
electron.

(I know the question is posed in an incorrect "billiard ball"
fashion.)

Any insights?

Jeff
_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l

Ludwik

http://csam.montclair.edu/~kowalski/life/intro.html