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.