Help Solve Problem: What Am I Doing Wrong?

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Homework Help Overview

The discussion revolves around a physics problem involving energy calculations for relativistic particles, specifically focusing on the relationships between energy, mass, and radius of particles such as protons and alpha particles. Participants are attempting to reconcile their results with expected values and are exploring the implications of classical and relativistic physics.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants are discussing various attempts to calculate energy values and ratios for different particles, questioning the accuracy of their results and the assumptions made in their calculations. There is also exploration of how to derive particle radii from mass and density, and confusion regarding the relationships between these quantities.

Discussion Status

Some participants have offered insights regarding the use of classical electron radius and its implications for other particles. There is ongoing exploration of how to derive certain values and clarify misunderstandings, with no explicit consensus reached yet.

Contextual Notes

Participants are grappling with the implications of using different values for particle radii and the resulting calculations, noting discrepancies in expected results. There is mention of specific values for radii that seem inconsistent with established physics, leading to further questioning and confusion.

Schmetterling
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Hello! I'm solving problems which come with their answers... but I get different results! Can you help me, please?
The problem statement and equations are in the attached images.

Homework Statement


(Image)
Also:
U=energy in Joules
β=v/c≈1 (relativ. particles)
μ0=4π×10-7

Homework Equations


(Image)
uB=B2/(2μ0), B=magnetic field in Teslas

The Attempt at a Solution


(a) Only substitute the values. I obtain -4.05×10-16 W= -2531 eV/s.

(b) \frac{(dU/dt)<sub>proton</sub>}{(dU/dt)<sub>electron</sub>}, only the term γ2proton/γ2electron remains and it is equal to (mc2)2proton/(mc2)2electron=2.96×10-7!
And it yields 1.86×10-8 for α particles. :-s

(c) Like process in (b), but equating instead of dividing. This gives γpro=γelect, and Uprot/Uelect= (mc2)prot/(mc2)elect = 1.84×103...

I have spent several hours in problem solving, now I'm tired and sleepy and can't see where is the mistakes(s), please, help!
 

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If you use the classical electron radius re for electrons, you should substitute this for other particles. This should give two additional factors of ##\frac{m_e}{m_p}##.
 
Ohhh! You're right! I didn't consider that, only took the given value for σT...:blushing:
Thanks!
 
Wait... How to obtain m_p from r_p (or viceversa) if don't know density?
I found already values for r_p and r_α, ~10^-16,-15 m, but I would like how to deduce them. Substitute p & α parameters into expression for r_e gives me radius ~10^-37!
 
Last edited:
Thanks, I have the value of class. e- radius, r_e= 2.818e-15, rather I need right values for radii of proton and alpha particles, because those I found are... odd:
r_p=2.1e-16
r_α=2.1e-15
How can be possible r_p<r_e?!
Another founded value for r_p is 8.6e-16, and r_alpha =4r_p...

I've tried to calculate them from formulae in http://en.wikipedia.org/wiki/Thomson_scattering and http://en.wikipedia.org/wiki/Classical_electron_radius:

http://upload.wikimedia.org/math/f/1/9/f196c5b29b4e0fed8f4710bedc522016.png & http://upload.wikimedia.org/math/5/3/d/53dc80a0e75009917114d545c93fc0a4.png=mc^2 without the factor 1/2, as it is said there... and I got 4.51E-034 for r_e & 8.72E-061 for sigma_T! :'(

I am increasingly confused!:( HEEEEEEELP!
 
Last edited:
Oh, I have it!, I have it! other factors are eliminated leaving only masses quotint^4!
 

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