Question

Calculate the field at the center of a long straight metal bar 2 cm in radius carrying a current of 300A ! that question is in my HW Is it even possible to calculate the magnetic flux density on the axis of the metal bar???

Answer 1

The field B will be proportional to the included current flux. The equation is B = (mu sub 0)(I)/(2 pi)(r), where I is the current within the region under consideration and r is the radial distance from the central axis. The fraction of the current within r is just (r/R)^2, where R is the radius of the bar. Solving this indicates B is proportional to r, which makes B zero at the axis of the bar. B(r)=(mu0)(I)(r)/(2 pi)(R^2)