Chapter 24, Problem 58A

To determine

The direction of the forces on the wire and their effect.

Explanation of Solution

Introduction:

When electric current flows through a wire, magnetic field is generated around the wire. The direction of the field is determined by the right hand rule. This field can be increased by winding the wire into coils. When placed under an external magnetic field it rotates.

In the electric motor wire is wound up in coils and is surrounded by magnets. DC current is supplied to this motor. When current flows through these wires it generates a magnetic field around the wire. This magnetic fieldunder the influence of the external magnets generates torque. The torque causes the coil to rotate. Note that the direction of force on the coil is decided by Fleming’s left hand rule.

For the coil to rotate, it requires a torque perpendicular to the axis of rotation. The forces on the wires along the axis of rotation are parallel to the axis. Hence, they don’t contribute to the torque

Conclusion:

For the coil to rotate it requires a torque perpendicular to the axis of rotation. The forces on the wires along the axis of rotation are parallel to the axis. Hence they don’t contribute to the torque