# (a) What is meant by electric resistance of a conductor ? (b) A wire of length L and resistance R is stretched so that the length is doubled and area of cross section halved. How will (i) resistance change and (ii) resistivity change ?

1
by siddiepalteja

2015-12-11T01:21:14+05:30

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a)
A
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A
Electric Resistance is the chracteristic property of a material which opposed the flow of electric current. It is denoted by "R" and its SI unit is ohm (Ω)

B
Let
new length,
new Area
and
new resistance be
respectively :
l' ,
A'
and
R'

Given, l' = 2l and A' = A/2

Since R = ρ l / A

So, R' = ρ * 2l / (A/2) = ρ * 4 l / A = 4 * (ρ l / A )
Since,
R = ρ *l/A ,
So :
R' = 4 * R

Resistivity depends on
the nature of material
not on the length/temperature or Area of cross-section.
So,
resistivity will remain CONSTANT