Problem regarding determining mass of neutrino

  • #1
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problem regarding determining mass of neutrino (urgent)

1. Homework Statement [/b]
It is found that the speed v of the neutrinos with 10 MeV of total energy is
(1- v/c) < 2x10^(-9) Estimate the mass of the neutrinos in terms of eV, and determine whether the value you find is an upper or lower limit.

My attempt:

I just start with (mc^2)(gamma) = 10Mev (m is the mass of neutrino, gamma is the Lorentz factor), and get v/c = ((1-((mc^2)/10MeV)^2)^1/2 after doing some algebra. Then, I solve the inequality and get m<632.45 eV. Is my approach and answer correct?

thx
 
Last edited:

Answers and Replies

  • #2
ehild
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Check the magnitudes.

ehild
 
  • #3
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If the question asks for the mass in terms of eV, do I multiply the mass in kg by c^2 then divide by e?
 
  • #4
ehild
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No, the mass is needed in eV-s. Have you transformed 10 MeV to eV-s ?

ehild
 
  • #5
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Well, I get m < 1.1259 x 10^-33 kg, is this answer correct?
 
  • #6
ehild
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The value you got for the mass in eV-s is wrong. No use to transform it to kg-s. Check your calculations: substitute the energy in eV-s.

ehild
 
Last edited:
  • #7
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But is my approach correct? Express 10MeV in terms of (gamma)mc^2, then find the expression of v/c after some algebra, and solve that inequality to get m.
 
  • #8
ehild
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Yes, your approach is correct, but read the text of the problem

" Estimate the mass of the neutrinos in terms of eV, and determine whether the value you find is an upper or lower limit. "

The equation you used (mc2)(gamma) = 10MeV is also correct. The rest mass in eV is just 107/gamma, and v/c is given :1-v/c<2˙10-9 .

No need to calculate the mass in kg-s.

I checked my calculation, and your result in the first post was correct. Sorry.

ehild
 
Last edited:

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