Newton's 3rd Law Coil in Magnetic Field

Question

When a current-carrying rectangular loop is placed in a magnetic field, the forces acting on either side of the loop which is perpendicular to the field provides a torque which rotates the loop.

However, according to Newton's 3rd Law, there should be some equal and opposite force acting on the object exerting the force. But in fields, it is the field that exerts forces on objects. Does that mean that the loop exerts an equal and opposite force on the magnet or on the magnet's field? How do these forces play out and what effect do they have on the magnet?

Adrian Howard · Answer

Newton's third law does cause magnets to have equal and opposite effects on each other, whether electromagnets or permanent magnets. The equal and opposite forces are transferred by the magnetic field. In an electric motor or generator, just as the field magnets are pushing /pulling on the armature via their magnetic fields, the armature is also pushing / pulling the field magnets. If you hold a small electric motor in your hand when it is started you can feel the anti spin ward torque of the motor housing as it applies spinward torque on the armature.

Answered by Adrian Howard on July 4, 2021

Newton's 3rd Law Coil in Magnetic Field

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