Coupled Oscillating Magnets
Requirements
- Neodymium magnets (x2)
- springs (x2)
- magnetic coil (x2)
- banana cables (x2)
- banana to BNC and oscilloscope (optional)
Description:
Each magnet is attached to a spring (both of which are relatively weak and have equal spring constants) and is positioned so that the equilibrium position of the spring with the magnet attached lies inside a copper coil. The leads of one coil are connected to the leads of the other coil with banana cables with opposite polarity. Provided the fields of both magnets are pointing in the same vertical direction, when one of the magnets is disturbed from equilibrium, it will induce a current in its coil; this current will flow in the opposite direction through the other coil, causing an opposite force on the second magnet. Thus, the magnet oscillators are coupled with a phase difference of 180º.
Location: J3, next to transformer demo. Uses the two yellow 400-turn coils, though any pair of identical coils should be okay.
Special precautions
The generated currents are no more than tens of mA.
Other ideas
Can connect one of the coils to a BNC, measuring the potential across the leads of the wire, which will be proportional to the current being induced by the changing magnetic fields. One can then see the oscillations in an oscilloscope and measure the springs' resonant frequency.
This demonstration can be used to introduce the electric monochord.