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

• A. the current source
• B. the lattice structure of the material of the rod
• C. the magnetic field
• D. the induced electric field due to the changing magnetic field

Answer 1

The Correct Option is C

In this problem, we are examining the behavior of a diamagnetic rod placed between the poles of an electromagnet. When the current through the electromagnet is switched on, the magnetic field generated interacts with the diamagnetic rod causing it to be pushed out of the magnetic field. The question asks us to identify the source of the energy that allows the diamagnetic rod to gain gravitational potential energy.

1. The diamagnetic rod is initially placed vertically between the poles of an electromagnet. Diamagnetic materials generate a magnetic field in opposition to an external magnetic field, which results in a repulsive force.
2. When the current is turned on, the electromagnet produces a magnetic field. The diamagnetic rod then experiences a force opposite to the direction of the external magnetic field.
3. This resultant force causes the rod to be pushed upwards, thereby increasing its gravitational potential energy.
4. The source of the work done to lift the rod comes from the magnetic field itself. In a typical scenario involving magnetic forces, it is this field energy that becomes converted into mechanical work.
5. Analyzing the other options:
   • The current source: While the current source provides the power to generate the magnetic field, it does not directly do the work on the rod. The role of the current source is to sustain the magnetic field.
   • The lattice structure of the material of the rod: The lattice structure of a diamagnetic material opposes external magnetic fields but does not provide energy to lift the rod.
   • The induced electric field due to the changing magnetic field: Faraday's Law of Induction concerns the induction of electric fields from changes in magnetic flux, but it is not the source of the mechanical work here.
6. Thus, the correct answer is the magnetic field. It is this energy that is converted into gravitational potential energy when the diamagnetic rod is lifted.

Hence, the work required to lift the rod, allowing it to gain gravitational potential energy, comes from the magnetic field.