Law of resistance, Specific resistance,conductance, conductivity
Law of Resistance:-
Resistance of a substance/ wire :
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Directly proportional to the
length, l
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Inversely proportional to the
area of cross section.
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As the length of wire increases
there is a chance of increase in number of electrons collusions resulting in increase
of resistance.
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As the length of wire
decreases, number of electrons collusions decreases resulting in decrease of
resistance.
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As the cross sectional area of
substance/wire increases, electrons get more area to move through resulting in
decrease of resistance.
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As the cross sectional area of
substance/wire decreases, electrons should move through a congested area
resulting in increase of resistance.
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Rαl
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Rα(1/A)
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Combining both the above
Rα(l/A)
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Where l is the length of
substance/wire and A is the cross sectional area of substance/wire.
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Here, the proportionality
constant is resistivity/specific resistance which depends upon the nature of
substance/wire.
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By removing proportionality
constant and putting equality constant
R=ρ*(l/A)
Specific resistance/resistivity:-
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Resistance between opposite
faces of a unit cube of that material.
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Measured in ohm-metres
Conductance:-
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Reciprocal of resistance
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Encouragement of substance to
flow of electrons through it.
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G=(1/R)
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Unit : mho (Ʊ)
Conductivity:-
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Reciprocal of resistivity.
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Conductance between the two
opposite faces of a unit cube.
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σ =(1/ρ)
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