# Alpha particle in a force field depiction

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## Summary:

Can someone give me an explanation of the below picture, please?
Hello, I was glazing through what I would consider an advanced physics textbook and I saw this image. It is a schematic picture of an alpha-particle in a field of an atom.

Now, can someone get me started on what (and why and how) is going on in it? Especially with the fraction with pi.

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Baluncore
2019 Award
Welcome to PF.
Can you please give a reference; Title; Author; ISBN; Page number.

mfb
Mentor
The alpha particle approaches a positively charged nucleus, it is repelled and its path is deflected by an angle ##\theta##. The rest is just geometry. The sum of the two angles with the fraction is ##\pi-\theta## because these two plus the ##\theta## angle must add up to ##\pi##. The dashed line is going through the point of closest approach. The particle trajectory is symmetric with respect to that line, so both sides of it have half of the ##\pi-\theta## angle.

The alpha particle approaches a positively charged nucleus, it is repelled and its path is deflected by an angle ##\theta##. The rest is just geometry. The sum of the two angles with the fraction is ##\pi-\theta## because these two plus the ##\theta## angle must add up to ##\pi##. The dashed line is going through the point of closest approach. The particle trajectory is symmetric with respect to that line, so both sides of it have half of the ##\pi-\theta## angle.
Thank you.