A thin diamagnetic rod is placed vertically between the poles of an electromagnet. When the current in the electromagnet is switched on, then the diamagnetic rod is pushed up, out of the horizontal magnetic field. Hence the rod gains gravitational po…

Question

A thin diamagnetic rod is placed vertically between the poles of an electromagnet. When the current in the electromagnet is switched on, then the diamagnetic rod is pushed up, out of the horizontal magnetic field. Hence the rod gains gravitational potential energy. The work required to do this comes from 1. the current source 2. the lattice structure of the material of the rod 3. the magnetic field 4. the induced electric field due to the changing magnetic field

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Answer: 1. the current source A static magnetic field exerts a force perpendicular to the motion of charges, so it does no net work itself. As the diamagnetic rod moves out of the field, the flux through the electromagnet changes and an emf is induced in its coil. To keep the current constant, the current source must supply extra energy against this emf. That energy appears as the gain in gravitational potential energy of the rod. So the work comes from the current source (option 1).

A thin diamagnetic rod is placed vertically between the poles of an electromagnet. When the current in the electromagnet is switched on, then the diamagnetic rod is pushed up, out of the horizontal magnetic field. Hence the rod gains gravitational po…

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