Question

Steel and copper wires of same length are stretched by the same weight one after the other. Young's modulus of steel and copper are $2 \times 10 ^ { 11 } \mathrm {~N} / \mathrm { m } ^ { 2 }$and$1.2 \times 10 ^ { 11 } \mathrm {~N} / \mathrm { m } ^ { 2 }$. The ratio of increase in length

• A. $\frac { 2 } { 5 }$
• B. $\frac { 3 } { 5 }$
• C. $\frac { 5 } { 4 }$
• D. $\frac { 5 } { 2 }$

Answer 1

Answer: (B)

$\frac { 3 } { 5 }$

Answer 2

$l = \frac { F L } { A Y } \Rightarrow \frac { l _ { S } } { l _ { c u } } = \frac { Y _ { c u } } { Y _ { S } }$(F,L and Y are constant)

∴ $\frac { l _ { s } } { l _ { c u } } = \frac { 1.2 \times 10 ^ { 11 } } { 2 \times 10 ^ { 11 } } = \frac { 3 } { 5 }$