Two wires of equal cross section but one made of steel and the other of copper, are joined end to end. When the combination is kept under tension, the elongations in the two wires are found to be equal. Find the ratio of the lengths of the two wires. Young modulus of steel `=2.0xx10^11Nm^-2` and that of copper `=1.1xx10^1Nm^-2`

Explanation

As the cross sections of the wires are equal and same tension exists in both the stresses developed are equal. Lelt the origiN/Al lengths of the steel wire and the copper wire be `L_s and L_c` respectively and the elongation in each wire be l.
`l/L_s=stress/(2.0x10^11nm^-2)`............i
`and l/L_c=stress/(1.1xx10^1Nm^-2)`............ii
Dividing ii by i
`L_s/L_c=2.0/1.1=20:11`