The windings of high-current electromagnets are often made of copper pipe. The current flows in the walls of the pipe, and the cooling water flows in the interior of the pipe. Suppose the copper pipe has an outside diameter of 1.2 cm and inside diameter of 0.8 cm.
What is the resistance of 30 m of this copper pipe?
What voltage must be applied to the pipe if the current is to be 600A?
How much will the resistance of the pipe change if it heats up from 20oC to 60oC?