I was reading about bimetallic strips and came to know that on heating it forms an arc like shape. I also read a sentence that the radius of such an arc can also be calculated which will be taught in the future grades. So I just wanted to know if there is any direct formula to find the radius of curvature? Also, I think it can be found out using A=l/r where A is the angle subtended. But then again, how can the angle be found? So what is the formula for radius?

I was reading about bi-metallic strips and came to know that on heating it forms an arc like shape. I also read a sentence that said the radius of such an arc can also be calculated which will be taught in the future grades. So I just wanted to know if there is any direct formula to find the radius of curvature? 
Also, I think it can be found out using $A=l/r$ where $A$ is the angle subtended. But then again, how can the angle be found? So what is the formula for radius?