Two different wires having lengths `L_(1)` and `L_(2) ` and respective temperature coefficient of linear expansion `alpha_(1)` and `alpha_(2)` are joined end - to - end . Then the effective temperature coefficient of linear expansion is :

Options

A. `( alpha_(1)L_(1) + alpha_(2)L_(2))/(L_(1) + L_(2))`
B. `2sqrt(alpha_(1) alpha)`
C. `(alpha_(1) + alpha_(2))/(2)`
D. `4(alpha_(1) alpha_(2))/(alpha_(1) + alpha_(2)) ( L_(2) L_(1))/((L_(2) + L_(1))^(2))`