The wavelength of a probe is roughly a measure of the size of a structure that it can probe in some detail. The quark structure of protons and neutrons appears at the minute length-scale of `10^(-15)m` or less. This structure was first probed in early 1970’s using high energy electron beams produced by a linear accelerator at Stanford, USA. Guess what might have been the order of energy of these electron beams. (Rest mass energy of electron = 0.511 MeV.)

Explanation

`p=(h)/(lambda)=(6.63xx10^(-34)Js)/(10^(-15)m)=6.63xx10^(-19)"kg m s"^(-1)`
Use the relativistic formula for energy :
`E^(2)=c^(2)p^(2)+m_(0)^(2)c^(4)=9xx(6.63)^(2)xx10^(-22)+(0.511xx1.6)^(2)xx10^(-26)-9xx(6.63)^(2)xx10^(-22)`,
the second term (rest mass energy) being negligible.
Therefore, `E=1.989xx10^(-10)J=1.24BeV`. Thus, electron energies from the accelerator must have been of the order of a few BeV.