Question

why we take the area of a wire equal to pi r^2​

Answer 1

HEY MATE HERE YOUR ANSWER

If you cut directly and squarely across the width of a wire then you will look at the end and it looks like a circle. The area of that end is the cross section area, which is Pi x r^2. A larger cross section area results in lower resistance per foot when the type of wire is the same.