MAGNETIC FIELDS SUMMARY You will measure how the magnetic field, B, produced by a coil varies with the current, I, in the coil. From your measurements, you w calculate the permeability constant Ho. Lastly you w use a magnet to induce a voltage in the coil. THEORY The magnetic field Batthe center of a circular coil (solenoid) of radius R with N turns that carries a current I is: HONI (1) center 2R. where Ho is the vacuum magnetic constant, Ho- 4m x107 Tesla. m /Amp. The field is directed along the axis of the coil and fairly uniform within. Instead of applying a current and inducing a magnetic field inside the coil, a current can be induced by changing the magnetic flux inside the coil. One way to do this is to change the (external) magnetic field strength inside the loop. This is how power is generated by a hydroelectric generating station. The voltage magnitude V induced in a single-turn coil by a changing magnetic flux, D, is (2) dt The flux, D, for a single loop of wire perpendicular to a magnetic field Bis BA (3) where A is the area of the loop, A-TR2 If the flux through a coil of wire is changed by moving a magnet through it, then equation 3 becomes approximately AB V NA (4) At