Two wires of equal cross-section but one made of steel and the other of copper are joined end to end. When the cobination is kept under tension, the elongations in the two wires are found to be equal elongations in the two wire are found to be equal. What is the ratio of the lengths of the two wires?
(Given, Young's modulus of steel `= 2 xx 10^(11) Nm^(-2)` and young's modulus of copper `= 1.1 xx 10^(11) Nm^(-2)`)

Options

A. `2 : 11`
B. `11 : 2`
C. `20 : 11`
D. `11 : 20`

Answer

c

Explanation

`Y = ("stress")/("strain")` or strain
`= ("strain")/(Y)` or `(Delta L)/(L) = ("stress")/(y)`
Since cross-section are equal and same tension exists in both the wires, therfore, the stress developed are equal. Also, `Delta L` is given to be the same for both the wires.
`:. L prop Y`
`:. (L_(s))/(L_(cu)) = (2 xx 10^(11))/(1.1 xx 1-^(11)) = (20)/(11)`