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First Experiment: The Meissner Effect

First Experiment: The Meissner Effect

This is the classic superconductor experiment of levitating a rare earth magnet above a superconductor. This experiment can be performed using the K1 superconductor kit. This experiment is shown in Figure 1. For this experiment I took a standard Styrofoam cup and trimmed the sides down to about ¾" high.

Before doing the experiment take the rare earth magnet and place it on top of the superconductor. Since the superconductor is not chilled with liquid nitrogen, it is not in a superconducting state and the magnet rests on top of the superconductor.

Now placed the superconductor in the center of the Styrofoam cup, then filled the cup with liquid nitrogen. Be careful. When you first pour the liquid nitrogen into the cup it will boil furiously until the temperature of the superconductor and Styrofoam cup are reduced.

Bring the rare earth magnet about 1/8 of an inch above the superconductor that is chilled in liquid nitrogen. Release the magnet. It floats above the superconductor.

The magnetic field of the rare earth magnet surrounds but does not penetrate the superconductor. The magnet generates current in the superconductor that creates a counter-magnetic force, expelling the magnet's magnetic field.

The rare earth magnet's magnetic field must be below the superconductor's critical magnetic field HC2. If the magnetic field were stronger than HC2 it would penetrate the superconductor and extinguish the superconductivity.

Second Experiment: Frictionless Magnetic Bearing

While the magnet is suspended above the superconductor, it can be set rotating, by tapping it gently or gently blowing air on a corner of the magnet using a plastic drinking straw. The rotating magnet will slow down and eventually stop due to air resistance.

Third Experiment: Superconductor Critical Temperature

The basic Meissner experiment may also be used to check the critical transitional temperature of the superconductor. To do so one needs to attach a thermocouple capable of reading extremely low temperatures. A suitable superconductor-thermocouple assembly is included in the Four-Point probe kit, discussed later.

Begin by placing a rare earth magnet on top of the superconductor. Pour liquid nitrogen into the Styrofoam cup. Record the temperature reading from the thermocouple. Mark the temperature that the rare earth magnet begins to float above the superconductor. This is the superconductor's critical temperature.

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