(IfT <<< mc^2 , make sure theprecisionof your calculator sufficient or use the non-relativistic
method below.)
If you know that the particle issuper-relativistic, so thatT >> mc^2 , then just usepc=Tand
life is easy.
If you know that the particle is highlynon-relativistic,T << mc^2 , then you can useT= p
2
2 m=
(pc)^2
2 mc^2 givingpc=√
2 mc^2 T.So, for example, compute the wavelength of a 100 eV electron. Thisis non-relativistic since 100 eV
¡¡ 510000 eV. Sopc=
√
106 ×100 eV or 10000 eV.λ=2 π 1973
pc=
12000
10000
= 1. 2 ̊A
3.5 Wave Particle Duality (Thought Experiments)
Richard Feynman (Nobel Prize for Quantum ElectroDynamics...) presents several thought experi-
ments in his Lectures on Physics, third volume.
For our first thought experiment, we will considertwo silt diffraction of light. Assume that
instead of using the screen, I use asensitive photo-detector. I measure the intensity of light as
a function of position near the screen and find the same set of maxima and minima that I did using
my eyes.