| Criteria | Marks |
|---|
| Provides a detailed analysis of the motion of the can AND the magnet; provides a detailed analysis of the energy transformations in the system | 7 |
| Analyses the motion of the can AND the magnet; provides an analysis of the energy transformations in the system | 6 |
| Describes the motion of the can and/or the magnet; describes the energy transformations of the magnet and/or can | 4–5 |
| Demonstrates some understanding of the motion of the can and/or the magnet and/or the energy transformations of both magnet and/or can | 2–3 |
| Provides some relevant information | 1 |
Sample answer: As the magnet swings from a high position towards the can, it loses gravitational potential energy and gains kinetic energy.
The motion of the magnet provides changing magnetic flux through the aluminium can. This change in flux is greatest when the relative motion of the magnet and can is greatest, and induces an emf according to
ε=−NΔtΔΦ
This emf gives rise to eddy currents in the can, which produces resistive heating as well as a magnetic field that opposes the movement of the magnet, according to Lenz’s law. The interaction of the magnetic fields of the magnet and the can, due to Eddy currents, also results in the can rotating clockwise initially. Over time, this results in a dampening of the magnet’s movement, and the interaction of the eddy currents’ magnetic field with the magnet results in the rotation of the can backwards and forwards, with diminishing amplitude as the total energy is ultimately converted to heat.
Answers could include: Reference to non-uniform, clockwise rotation of the can
