A moving coil galvanometer is a sensitive device which can be used as a detector to check if a curretn is flowing in a circuit. A galvanometer works on the principle that a current carrying coil placed in a radial magnetic field experiences a deflecting torque whose magnitudes is directly proportional to the electric current passing through it. The deflection phi is indicated by a pointer and is give as phi = (NAB)/k cdot I. A galvonometer can be used to measure electric current flowing througha circuit direcly in ampere and its submultiples. For this purpose we join a small resistance 'r_s' in parallel to the galvonometer. Such a shunted galvonometer is called an ammeter. If a galvanomter, having a resistance R_G, givens full scale deflection for a current I_g and we want to measure a current ranging from 0 - I_g A, then the value of shunt resistance will be r_s = (R_G cdot I_g)/(I - I_g) How is a radial magnetic field obtained?