Question

A steel wire of length 4.7m and cross section area $3\times {10}^{-6}{m}^2$ stretches by the same amount as a copper wire of length 3.5 m and cross-section area $4\times {10}^{-6}{m}^2$ under a given load. The ratio of Young's modulus of steel to that of copper is

• A. 1.8
• B. 3.6
• C. 0.6
• D. 8.7

Answer 1

The correct option is A

1.8

Since the load and extension are the same, $\Rightarrow$ the ratio $\frac{YA}{l}$ sould remain constant.

Therefore,

$\frac{Y_s}{Y_c}=\frac{A_c{l}_s}{A_s{l}_c}$

$=\frac{4\times {10}^{-6}\times 4.7}{3\times {10}^{-6}\times 3.5}$

$=1.8$