55. (a) The charge that strikes the surface in time ∆tis given by ∆q= i∆t, where iis the current. Since each particle carries charge 2e, the number of particles that strike the surface is Nqeite===××=×−−∆∆22025 1030216 1023 1061912...AsCchbgch(b) Now let Nbe the number of particles in a length Lof the beam. They will all pass through the beam cross section at one end in time t = L/v, where vis the particle speed. The current is the charge that moves through the cross section per unit time. That is, i= 2eN/t= 2eNv/L. Thus N = iL/2ev. To find the particle speed, we note the kinetic energy of a particle is K==××=×−−2020 10160 1032 1061912MeVeVJ / eVJ .chchSince Kmv=122,then the speed isvKm=2. The mass of an alpha particle is (very nearly) 4 times the mass of a proton, or
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This note was uploaded on 06/03/2011 for the course PHY 2049 taught by Professor Any during the Spring '08 term at University of Florida.