How Does a Gold Nucleus Affect an Alpha Particle at Close Range?

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Homework Help Overview

The discussion revolves around the interaction between an alpha particle and a gold nucleus, specifically focusing on the electric field generated by the gold nucleus at a close distance and the resulting acceleration of the alpha particle. The problem is situated within the context of electrostatics and nuclear physics.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss using Coulomb's law to calculate the electric force between the alpha particle and the gold nucleus, questioning the appropriate method for finding the electric field and acceleration. There is also a consideration of whether to use force equations directly or to derive the electric field first.

Discussion Status

The conversation is active, with participants offering different approaches to the problem. Some express uncertainty about the methods, while others clarify the relationship between the electric field and force calculations. There is no explicit consensus on the preferred method, but guidance has been provided regarding the relevance of the electric field in the context of the problem.

Contextual Notes

Participants acknowledge the complexity of the physics involved and express varying levels of confidence in their understanding of the concepts. There is an emphasis on the need to consider the electric field as part of the solution.

echau
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An alpha particle approaches a gold atom head on, stops, and turns around at a distance of 10^-11m from the nucleus. What is the electric field due to the gold nucleus at this point? Ignore the effects of the gold atom's orbiting electrons. What is the acceleration of the alpha particle when it is stopped? An alpha particle is a helium nucleus, composed of two protons and two neutrons.

Can anyone help me with this problem? I'm just not understanding it...any help would be appreciated.
 
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The force momentarily stopping the alpha particle is the repulsive electric force that the gold nucleus exerts on the alpha particle. Use Coulomb's law to find the force between the charges at the given distance. (What's the charge of the gold nucleus? What's the charge of the alpha particle?) Then apply Newton's 2nd law to find the acceleration.
 
The alpha particle (nucleus of He atom) has + charge proportional to Z=2 (2 protons) and the gold nucleus has + charge proportional to Z=79 (79 protons).

So this becomes an electrostatic force problem - the alpha stops.

Remember coulombs law and coulomb force.

What is the electric field cause due to 79q, where q is the magnitude of charge on a proton?

acceleration, a = F/m.
 
Thanks for the replies!

Should I use F=kq1q2/r^2? then plug it into F=ma?

or should I find E=kq/r^2 and plug it into F=qE?

Sorry if these are very simplistic questions...Physics is hard for me =/
 
echau said:
Should I use F=kq1q2/r^2? then plug it into F=ma?

or should I find E=kq/r^2 and plug it into F=qE?
The two approaches are identical. Take your pick.
 
thank you :) i really appreciate the help!
 
The two approaches are (pedagogically) NOT identical ...
the first approach ignores the E-field, which WAS the Question.
 
Good point, since one of the questions was to find the electric field. :blushing:

As far as figuring out the acceleration, the two methods for finding the force are identical. But since you have to find the electric field anyway, obviously you would use that result to finish the problem.
 

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