# Charge-to-mass ratio of electron/proton

by jdc22
Tags: chargetomass, electron or proton, ratio
 P: 1 1. The problem statement, all variables and given/known data The Helmholtz coil current = 2.45 A, the magnetic field = 1.91 x 10^(-3) T, the accelerating voltage = 295 V, and the beam radius = .03m. a) Calculate the e/m ratio of an electron. Show that e/m = 2V / r²B² b) During the initial use of this experiment, physicists also knew the charge-to-mass ratio of a hydrogen ion, approximately 9.58 x 10^7 Coulombs/kg. If you had little knowledge of atomic structure, what two interpretations could you place on the differences between the two ratios? 2. Relevant equations PE = Ve KE = 1/2mv² Fmag = evB Fcent = mv²/r 3. The attempt at a solution a) Ve = 1/2mv² v = √(2Ve / m) ; v² = 2Ve/m Fmag = Fcent evB = mv²/r r = mv/Be I can't seem to get past this part of the derivation. I've tried subbing in √(2Ve / m) into r = mv/Be but it turns out too messy. b) I'm not too sure about the second part at all.. in what kind of context should I be thinking about the ratios?

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