0.5 mm 300 mm -250 mm B Magnesium A 2000 mm² = E=45 GPa α = 26 x 10-6/°C Aluminum A = 800 mm² E = 75 GPa a = 23 x 10-6°C At room temperature (20°C) a 0.5-mm gap exists between the ends of the rods shown. At a later time when the temperature has reached 120°C.