1. The problem statement, all variables and given/known data A rectangular current-carrying coil, with side lengths a and b has N turns. The current, I is stable. The coil is shorter than its width. Calculate the magnitude of the magnetic field at the centre of the rectangle. 2. Relevant equations The law of Biot-Savart (I think). 3. The attempt at a solution Stupid (I know) - but I am unsure of what to do with the element of Biot-Savart, which concerns the radius. Perhaps I could divide the rectangle into 4 segments - calculate each segment: Bsegment = (mu o/4p )(I/R)(cosa +cosb ) and then add them up? Please, please help me as it is part of a larger assignment involving the effect of a magnetic field on a current-carrying coil.