Two wires of same length and radius are joined end to end and loaded. The Young.s modulii of the materials of the two wires are `Y_(1) and Y_(2)`. If the combination behaves as a single wire them its Young.s modulus is

Explanation

`e = e_1 + e_2` but `e = (F(2l))/(AY_(eq)), e_1 = (Fl)/(AY_1), e_2 = (Fl)/(AY_2)`
`(F(2l))/(AY_(eq)) = (Fl)/(AY_1) + (Fl)/(AY_2)`
`(2)/(Y_(eq)) = (1)/(Y_1) + (1)/(Y_2) rArr Y_(eq) = (2Y_1Y_2)/(Y_1+Y_2)`