physics
posted by sand .
A 90 cm length of steel wire with a diameter of 0.5 mm is stretched between the inside walls of an oven the wire is just taut with no tension when the temperature in the oven is 250 °C. What is the the tension force in the wire when the oven cools to a temperature of 150 °C? The distance between the oven walls does not change as the oven cools.

The length of the wire IF UNSTRETCHED decreases by an amount
delta L = 90 cm*alpha*100C,
where alpha is the coefficient of thermal expansion of steel. Look that up.
But since the wire does not stretch, it is under tension T that can be calculated using Young's modulus of steel, E. Look that one up, too.
Stress = strain * E
= (deltaL/L) *E
= E*alpha*deltaT
(L cancels out)
The tension force is the stress times the wire crosssectional area.