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Chapter 6 Electrical properties
Ohm’s law
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• Ohm's Law: V = I R
voltage drop (volts = J/C)
C = Coulomb
resistance (Ohms)
current (amps = C/s)
฀
1
• Conductivity, 
• Resistivity, :
-- a material property that is independent of sample size and
geometry
฀
RA
l
surface area
of current flow
current flow
path length
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Which will have the greater resistance?
Analogous to flow of water in a pipe
Resistance depends on sample geometry and
size.
D
2D
฀
R12
D
2


 


28
D2
฀
฀
2
฀
R2
2D
2


 


2
D2R1
8
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Further definitions
J = E <= another way to state Ohm’s law
J current density
E electric field potential = V/
flux a like
area surface
current
A
I
Electron flux conductivity voltage gradient
J = (V/ )
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