A demonstration performed in class showed that a current-carryingwire placed in

Question

A demonstration performed in class showed that a current-carryingwire placed in a
magnetic field will gain kinetic energy as the wire accelerates inresponse to the magnetic
force. However, in applying our definition of work, we realize thatthe magnetic field
cannot do work on a charged particle because the force on theparticle is perpendicular to
its motion. From this we conclude that the magnetic force is anexception to the rule.

If this statement is true, prove it. If false, show why it isfalse. This one’s subtle!

Explanation / Answer

the current is going upwards, -Lorenz's force is directed to the left; What would happen if there was no wire (the charged particles werein free space)? They would turn to the left. The wire doesn't let them turn left (you guys are right: there is apath). So the particles are exerted not only to the magnetic force,but also to the force F of the reaction of the wire (it is directedto the right). Accoarding to the 3d Newton's law the particles apply force T(T=-F) for the wire. So, the work that accelerates the cabel is done by the force T.

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