A rod of length 1000 mm and co-efficient of linear expansion α = 10-4  per degree is placed symmetrically between fixed walls separated by l00l mm. The Young's modulus of the rod is 1011N/m2. If the temperature is increased by 20°C, then the stress developed in the rod is (in N/m2)

The change in length of rod due to increase in temperature in absence of walls is∆l = lα ∆T = 1000×10-4×20 mm      = 2 mmBut the rod can expand upto 1001 mm only.At that temperature its natural length is = 1002 mm.∴ compression = l mm ∴  mechanical stress= Y = ∆ll = 1011×11000 = 108 N/m2