- #1
CAF123
Gold Member
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I understand that the relativistic eqn that applies to all particles in all frames of reference and that works for both massless and massive particles is E^2 = (p^2)(c^2) + (m^2)(c^4).
I then attempted a small question:
Deduce the de Broglie wavelength of thermal neutrons from a nuclear reactor which have k.E ~(3/2)kT.
I have the correct answer and know how to solve the problem (which is why I did not post in homework forum), however, I found the answer by finding k.E by the above formula and then equating this to (1/2)mV^2 and solving for v. After finding v, I found p = mv and therefore the de Broglie wavelength.
My question is: when I instead use the relativistic eqn at the top (which according to my notes works in all frames of references) I yield a negative under the square root. Why is this so? Why aren't things consistent?
For reference, I used E = 6.1 x10^-21 J in both attempted methods.
Many thanks
I then attempted a small question:
Deduce the de Broglie wavelength of thermal neutrons from a nuclear reactor which have k.E ~(3/2)kT.
I have the correct answer and know how to solve the problem (which is why I did not post in homework forum), however, I found the answer by finding k.E by the above formula and then equating this to (1/2)mV^2 and solving for v. After finding v, I found p = mv and therefore the de Broglie wavelength.
My question is: when I instead use the relativistic eqn at the top (which according to my notes works in all frames of references) I yield a negative under the square root. Why is this so? Why aren't things consistent?
For reference, I used E = 6.1 x10^-21 J in both attempted methods.
Many thanks