Question
The following four wires are made of 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 :
As $$\gamma = \frac{{F \times L}}{{\Delta L \times A}} = \frac{{mg.l}}{{\Delta L.A}}$$
or $$\Delta L = \frac{{mgL}}{{4.A}}$$
$$ \Rightarrow \Delta L \propto \frac{L}{A},$$ which is maximum for option (A).