Two exactly similar wires of steel `(y_(s)=20xx10^(11)"dyne"//cm^(2))` and copper `(y_(c)=12xx10^(11)"dyne"//cm^(2))` are stretched by equal forces. If the total elongation is 1 cm, elongation of copper wire is

Options

A. `3//5` cm
B. `5//3` cm
C. `3//8` cm
D. `5//8` cm

Answer

D

Explanation

`(l_(Cu))/(l_(s))=(y_(s))/(y_(Cu)) therefore l_(Cu)=(20xx10^(11))/(12xx10^(11))xxl_(s)=(5)/(3)l_(s)`
Now, `l_(Cu)+l_(s)=1 therefore l_(Cu) =1 therefore (8l_(Cu))/(5)=1`
`l_(Cu)=5//8 cm.`