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nagle_phys2020_fa07_lecture2

# nagle_phys2020_fa07_lecture2 - Size Scales atomic size ~...

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1 28 Reminder – CAPA Homework due this Friday - Electrostatistics Prelab/Lab for next week 29 Size Scales: atomic size ~ 10 -10 m nuclei size ~ 10 -15 m Mass Scales: m(electron) << m(proton) ~ 1 : 1800 Electric Charge: q(proton) = -q(electron) 30 Units of Charge: Charge of one electron: q = - e = - 1.602 x 10 -19 [C] SI unit of charge is the Coulomb [C]. Charge of one proton: q = + e = + 1.602 x 10 -19 [C] 31 The charge of the proton is opposite in sign to the electron, but exactly the same magnitude to the best precision we have ever measured. Kind of a nice symmetry! 32 You might wonder about why the proton is almost 2000 times heavier than the electron, but has the same charge magnitude? In fact, the proton is made up of quarks with charge +2/3 e and -1/3 e. However, we never see these quarks outside the proton. They are mostly important in very high energy reactions. 33 How large is one Coulomb of charge? number of electrons x charge per electron = total charge N x (1.602 x 10 -19 [C]) = 1.0 [C] N = 1.0 [C] / (1.602 x 10 -19 [C]) N = 6.3 x 10 18 electrons in one [Coulomb] !

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