Question

$A$ and $B$ are two wires. The radius of $A$ is twice that of $B$. They are stretched by the same load. Then the stress on $B$ is

• A. equal to that on $A$
• B. four times that on $A$
• C. two times that on $A$
• D. half that on $A$

Answer 1

The correct option is B four times that on $A$

$stress=\frac{Force}{Area}$
$\therefore stress\propto \frac{1}{\pi r^2}$
Thus, $\frac{S_B}{S_A}={\left[\frac{r_A}{r_B}\right]}^2=(2{)}^2\Rightarrow S_B=4S_A$