Question

A composite rod is made by joining end to end two rods P and Q of same cross-section. At 25°C the length of composite rod is 1 m of which 0.3 m is of P. The composite rod is heated to 125°C. Its length increases by 1.91 mm. Coefficient of linear expansion of P = 1.7 x 10^-5 (°C)^-1. The coefficient of linear expansion of Q is

(1) 2 x 10^-4 (°C)^-1

(2) 1.5 x 10^-5 (°C)^-1

(3) 2 x 10^-5 (°C)^-1

(4) 2.5 x 10^-4 (°C)^-1

Answer 1

(3) 2 x 10^-5 (°C)^-1

Let l_P and l_Q be length of rod P and Q at 250C. Given

be increase in length of P and Q when temperature is raised to 125°C. Then