# Which interactions proceed by which fundamental force?

1. Apr 24, 2015

### cp255

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I have been getting ready for my Intro to Modern Physics final. The professor likes to ask a lot of questions like

Which of the following neutron reactions proceeds via the electromagnetic force?

Or something like this...

I have been looking all over the internet and my text book. All I can find is kind of vague guidelines for this. How would I go about figuring it out?

I think the answers are Weak, EM, Strong, Weak (Just not completely sure why).

Last edited: Apr 24, 2015
2. Apr 24, 2015

### Orodruin

Staff Emeritus
You say you are not sure why, but what do you think?

3. Apr 24, 2015

### cp255

I think I might have figure it out.

a) The weak force is needed to produce nutrinos.
b) If there are photons this implies EM
c) Strong because of baryons.
d) Weak because of neutrinos.

4. Apr 25, 2015

### Orodruin

Staff Emeritus
Correct. Neutrinos only interact through the weak interactions.
What about $\pi^+ \to \mu^+ + \nu_\mu + \gamma$? This has photons, but also neutrinos.
What about $K^+ \to \pi^+ + \pi^0$ or $\Lambda \to p + \pi^-$?
Correct.

5. Apr 25, 2015

### vela

Staff Emeritus
If you're familiar with Feynman diagrams, try drawing the ones that represent a particular decay.