Chapter3_2

# Chapter3_2 - A mole of hydrogen molecules i.e H 2 has a...

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PHY3063 R. D. Field Department of Physics Chapter3_2.doc University of Florida Some Important Constants (in 1900) (A) The speed of light in a vacuum: s m c / 10 997925 . 2 8 × = (B) Avogadro’s number: mole N A / 10 022 . 6 23 × = N A is the number of entities in a mole of anything. A mole is the amount of any substance that contains as many entities as there atoms in 12 grams of Carbon-12 . N A is the number of Carbon-12 atoms in 12 grams of Carbon-12. Thus, ) 1 ( 12 12 AMU N g A × × = and 23 27 3 10 02 . 6 10 66 . 1 / 10 ) 1 /( 1 × × = = kg kg AMU g N A N A is the number of molecules in a mole of any gas. N A is the link between microphysics and macrophysics. It is large because atoms and molecules are small. (C) Mass of the hydrogen atom: kg M H 27 10 67 . 1 × = M H is equal to the mass of a proton, M p , to within 1 part in 2000.
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Unformatted text preview: A mole of hydrogen molecules ( i.e. H 2 ) has a mass of 2 grams. Thus grams M N M N M N p A H A H A 2 2 2 2 = ≈ ≈ (D) The magnitude of the charge of an electron e: C e 19 10 6 . 1 − × = The charge carried by a mole of singly charged ions (each with charge e) is called Faraday’s Constant F = N A e = 96,500 C . (E) The ratio of charge to mass for an electron and proton: kg C m e e / 10 76 . 1 / 11 × = kg C M e p / 10 6 . 9 / 7 × = Determined by J.J. Thomson in 1897 by bending beams of protons and electrons in a magnetic field. (F) The mass of an electron: kg m e 31 10 11 . 9 − × = This was inferred from e and e/m e . Not known very well in 1900!...
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