A magnet is swinging as a pendulum. Close below it is an aluminium (non-ferromagnetic) can. The can is free to spin around a fixed axis as shown.
Analyse the motion and energy transformations of both the can and the magnet. (7 marks)
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→ When the magnet swings down from its high position toward the can, its gravitational potential energy transforms into kinetic energy.
→ As the magnet moves, it creates changing magnetic flux through the aluminium can. This flux change is strongest when there’s the fastest relative motion between the magnet and can.
→ The induced emf is described in the equation
→ This emf creates eddy currents in the can, which produce both heat and a magnetic field. Following Lenz’s law, this magnetic field opposes the magnet’s motion.
→ The magnetic fields from both the magnet and the eddy currents interact, causing the can to initially rotate clockwise.
→ Eventually, this interaction dampens the magnet’s swing. The magnetic interaction between the eddy currents and the magnet causes the can to rotate back and forth with decreasing amplitude, as the system’s energy gradually converts to heat.
→ When the magnet swings down from its high position toward the can, its gravitational potential energy transforms into kinetic energy.
→ As the magnet moves, it creates changing magnetic flux through the aluminium can. This flux change is strongest when there’s the fastest relative motion between the magnet and can.
→ The induced emf is described in the equation
→ This emf creates eddy currents in the can, which produce both heat and a magnetic field. Following Lenz’s law, this magnetic field opposes the magnet’s motion.
→ The magnetic fields from both the magnet and the eddy currents interact, causing the can to initially rotate clockwise.
→ Eventually, this interaction dampens the magnet’s swing. The magnetic interaction between the eddy currents and the magnet causes the can to rotate back and forth with decreasing amplitude, as the system’s energy gradually converts to heat.