In a bi-metallic strip of copper and iron, when heated, the strip is bended into the iron's way. Why?

A bi-metallic strip is used to convert a temperature change into mechanical displacement.
The strip consists of two layers, usually iron and copper. The two layers are joined together to form the strip.
Owing to the difference in the constants of expansion of the two materials, a flat strip will bend one way (toward the iron part) if heated.
The linear thermal expansion coefficient relates the change in temperature to the change in a material's linear dimensions. It is the fractional change in length of a bar per degree of temperature change.
You see from the table that cooper has thermal expansion coefficient value-17 and iron-12.When heated
cooper expands more than iron , so the strip is bended into the iron's way.

https://en.wikipedia.org/wiki/Coefficient_of_thermal_expansion