Give the equation of motion of the coil-meter, and derive the relationships that must exist if the damping of the movement is to be critical. A moving-coil instrument has a rectangular coil wound on an aluminum former of resistivity 2.7u92-cm. The sides of the former, each of effective length 3cm, move in a radial field of uniform flux density 0.15wb/m (1500G) against a control torque of 18x106 N-m (180dyn-cm) per radian. the width of the former is 2cm, the ends being effectively outside the magnet field, and the moment of inertia of the moving system is 2cm, the ends being effectively outside the magnet field, and the moment of inertia of the moving system is 8x10-8ka-m. botto- sariq b