Magnetic flux linkage = BAN B=magnetic field strength per unit area A=Area of conductor moved through the magnetic field N=Number of coils I don't understand when my physics text book says the area of a single coil of wire moved through the magnetic field is π×radius of coil^2 as most of the coil is just empty space. So why does the A include the entier cross section of the coil, including the empty space? Surely empty space moving through a magnetic field has no effect on magnetic flux linkage? Yet the formula includes this empty space. What is the reason for this?