Consider two pieces of wires, one of steel and other of rubber. Suppose, both are of equal length L and of equal area of cross-section (a).
Let each be stretched by equal forces, each being equal to F. The change in length of the rubber wire (lr) is more than that of the steel (ls),
i.e., lr > ls
If Ys and Yr are the Young'* moduli of steel and rubber respectively.
Then by definition of Young'* modulus,
Ys = FL/als and Yr = FL/(a/r)
⇒ Ys/Yr = lr/ls
As lr > ls, therefore, lr/ls > 1, i.e., Ys/Yr > 1
or Ys > Yr.
i.e., the young'* modulus of steel is more than that of rubber. Hence, steel is more elastic than rubber.
