Question
The following four wires are made of the same material. Which of these will have the largest extension when the same tension is applied?
A.
$$length=50\,cm, \,\,diameter=0.5 \,mm$$
B.
$$length = 100 \,cm, \,\,diameter= 1 \,mm$$
C.
$$length= 200 \,cm, \,\,diameter= 2 \,mm$$
D.
$$length=300 \,cm, \,\,diameter =3 \,mm$$
Answer :
$$length=50\,cm, \,\,diameter=0.5 \,mm$$
Solution :
$$Y = \frac{{\frac{T}{A}}}{{\frac{{\Delta \ell }}{\ell }}}\,\,\, \Rightarrow \Delta \ell = \frac{{T \times \ell }}{{A \times Y}} = \frac{T}{Y} \times \frac{\ell }{A}$$
Here, $$\frac{T}{Y}$$ is constant. Therefore, $$\Delta \ell \propto \frac{\ell }{A}.$$
$$\frac{\ell }{A}$$ is largest in the first case.