20.37. Set Up: The coil as viewed along the axis of rotation is shown in Figure 20.37a for its original position and in Figure 20.37b after it has rotated Figure 20.37 Solve: (a) The forces on each side of the coil are shown in Figure 20.37a. and The net force on the coil is zero. and so The forces on the coil produce no torque. (b) The net force is still zero. and the net torque is The net torque is clockwise in Figure 20.37b and is directed so as to increase the angle Reflect: For any current loop in a uniform magnetic field the net force on the loop is zero. The torque on the loop depends on the orientation of the plane of the loop relative to the magnetic field direction. 20.38. Set Up: The torque on a solenoid is The angle is the angle between the axis of the solenoid and the direction of the field. Solve: (a) (b) and (c) and 20.39. Set Up: The area A is related to the diameter D by Solve: is proportional to Increasing D by a factor of 3 increases by a factor of 20.40. Set Up: For a long, straight wire,
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