explain y is it necessary to use cylindrically concave pole pieces in construction of MCG..?!!?
Its necessary to use cylindrically concave pole pieces in the construction of moving coil galvanometer because for the moving coil galvanometer the magnetic field B must be parallel to the plane to which the coil belongs.Only this will help in conforming the fact that the angle involved is 90 degrees and thus the equation of torque : Deflecting torque = NIBA sin(z) results in NIBA where N is the number of turns , I is the current , B is the magnitude of magnetic field and A is the area of cross-section and z is the angle of twist.The cylindrically concave mirror helps in conforming this.