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 the order of energy of these electron beams. (Take wavelength of a proton = $10^{-15}m$ ; rest mass of energy of electron = $0.511\: MeV$)
