Question

Two donut-shaped magnets are stacked on top of each other with a wooden dowel in the center. The south poles of the magnets are facing each other. Once the upper magnet is released, it accelerates downward and stops 1 cm above the lower magnet. How does the energy stored in the magnetic field change? (1 point)
Responses

Some of the energy stored is converted into kinetic and thermal energy.
Some of the energy stored is converted into kinetic and thermal energy.

All of the energy stored is converted into kinetic and thermal energy.
All of the energy stored is converted into kinetic and thermal energy.

Some of the energy stored is converted into kinetic, thermal, and gravitational energy.
Some of the energy stored is converted into kinetic, thermal, and gravitational energy.

All of the energy stored is converted into kinetic, thermal, and gravitational energy.
All of the energy stored is converted into kinetic, thermal, and gravitational energy.

Answer 1

The magnetic-field energy increases.

As the upper magnet falls it loses gravitational potential energy; part of that goes into increasing the magnetic potential energy (you do work against the repulsive magnetic force), part into transient kinetic energy, and finally into thermal energy when the motion is damped. The net result is a larger energy stored in the magnetic field at the closer 1 cm separation.