A steel rod 10 min in diameter and 1 m long is heated from 200C to 1200C, E = 200 GPa and
$\alpha$ = 12 x 10-6 per 0C. If the rod is not free to expand the thermal stress developed is
(a) 120 MPa (tensile) (b) 240 MPa (tensile)
(c) 120 MPa (compressive) (d) 240 MPa(compressive)