Suppose that we can use wire of 1.0-mm diameter to make either a single loop of wire or a solenoid, and we wish to compare, for a given current, the magnetic fields at the center of each.

a. Use the Biot-Savart law to derive an expression for the magnetic field magnitude at the center of a circular current loop. Express your answer in terms of the current I, loop radius R, and magnetic constant muknot.
b. Compare the magnitude of the magnetic field at the center of a circular loop of radius 40 mm with the magnitude of the magnetic field at the center of a solenoid of the same radius and with 3.0 turn per millimeter. Assume the current is the same through the current loop and the solenoid.