Transcript Resistance and Ohm’s Law ECE 201 1

Resistance and Ohm’s Law
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Resistance and Ohm’s Law
• The ability of materials to oppose the flow of
electric charges is known as resistance. The
circuit component that models this property is a
resistor, as shown below. The value of the
resistor is R.
• The Unit of R is Ohms (Ω).
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Ohm’s Law
• Georg Simon Ohm experimentally
observed that there is a direct relationship
between the current flowing through a
material and the voltage difference across
it’s terminals.
• This is expressed as Ohm’s Law, the most
common form of which is v = iR.
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Reference choices for v, i
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Alternate forms of Ohm’s Law
v  iR
v
i
R
v
R
i
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Conductance, G
• Conductance is the reciprocal of
resistance
• Symbol is G
• Unit is S (siemens)
• Alternate unit is mho (ohm spelled
backwards)
• Used to simplify calculations
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Power in a resistor
p  vi
p  (iR ) R  i R
2
v v
p  v  
R R
2
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