# Rutherford scattering experiment question

1. Dec 15, 2011

### stony

Rutherford scattering experiment question (urgent)

1. The problem statement, all variables and given/known data
I need to find the value of the electrical force between the alpha particle and the nucleus of the atom at the point of closest approach.

Closest approach = 7.27 x 10^-14 m
Charge on atom = (79 * 1.60 x 10 ^-19) C
initial kinetic energy of alpha particle = 5.00 x 10^-13 J

2. Relevant equations

I think you're supposed to use [Epe = (kq1q2)/r] or [Fe = (kq1q2)/r^2]

3. The attempt at a solution

(8.99x10^9)(2*1.60x10^-19)(79*1.60x10^-19)
________________________________________
7.27x10^-14

Am I trying to solve this right? Need an answer ASAP please!

Thank you.

2. Dec 16, 2011

### Andrew Mason

Re: Rutherford scattering experiment question (urgent)

Your are correct to use the Coulomb potential. What is the atomic nucleus that is scattering the alpha particle (how many protons and neutrons)?

What is the kinetic energy of the alpha particle at the point of closest approach? What is its potential energy? You should work out an algebraic solution first and then plug in the numbers. Otherwise it is difficult to see your reasoning.

AM

3. Dec 16, 2011

### stony

Re: Rutherford scattering experiment question (urgent)

It doesnt outright say what the nucleus is, but since it has 79 protons I guess that means it's gold.

Kinetic energy at point of closest approach = 0
Potential energy at the point of closest approach = the kinetic energy that it started with

Sorry, what do you mean it's difficult to see my reasoning?

I just tried it using this equation [Fe = (kq1q2)/r^2] but the answer I got is 6.8799, which is also wrong. I don't understand why this equation won't give me the right answer, am I not using it right?