Question

(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 ?

Answer 1

a)
A
a
a
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

Answer 2

The property of resistor to prevernt the passage of current freely

Various resistors had various resistances