First slide
Stress and strain

Two wires are made of the same material and have the same volume. The first wire has cross-sectional area A and the second wire has cross-sectional area 3A. If the length of the first wire is increased by l on applying a force F, how much force is needed to stretch the second wire by the same amount?


 Young's modulus, Y=FlAΔl

Since initial volume of wires are same

 Their areas of cross sections are A and 3 A  and lengths are 3l and l respectively.

For wire 1,

Δl=FAY3l            ...........(i)

  For wire 2 , let F' force is applied 


Δl=F'3AYl         ..........(ii)

From the equations (i) and (ii)



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