ch26-p055 - 55. (a) The charge that strikes the surface in...

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55. (a) The charge that strikes the surface in time t is given by q = i t , where i is the current. Since each particle carries charge 2 e , the number of particles that strike the surface is N q e it e === × × ∆∆ 22 025 10 30 216 10 23 10 6 19 12 .. . As C ch bg c h (b) Now let N be the number of particles in a length L of the beam. They will all pass through the beam cross section at one end in time t = L / v , where v is the particle speed. The current is the charge that moves through the cross section per unit time. That is, i = 2 eN / t = 2 eNv / L . Thus N = iL /2 ev . To find the particle speed, we note the kinetic energy of a particle is K == × × = × −− 20 20 10 160 10 32 10 61 9 1 2 MeV eV J / eV J . c hc h Since Km v = 1 2 2 ,then the speed is vK m = 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.

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