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

• A

  The current source

• B

  The magnetic field

• C

  The lattice structure of the material of the rod

• D

  The induced electric field due to the changing magnetic field