A steel wire of length 2o cm and uniform cross-section 1mm2 is tied rigidly at both the ends. The temperature of the wire is altered from 40°C to 20°C. Coefficient of linear expansion for steel α =1.1 x 10-5 /°C and f for steel is 2 .0 x 1011 N/m2 . The change in tension of the wire is