DEMONSTRATION #2

A Superconductive Switch

When a superconductor is in the normal state the resistance to the flow of current is quite high compared to the superconducting state. Because of this, a simple resistance switch can be easily demonstrated.

Material:

• YBCO superconductive wire with attached leads

• 2 C batteries with holder

• 3 volt flash light bulb with holder

• liquid nitrogen

• dewar or styrofoam cup

Procedure:

1. Connect superconductor, light bulb and batteries as shown in Figure (20).
2. When the superconductor is at room temperature it is in the normal state and will have high resistance.The bulb will not light.
3. Place the superconductor into the liquid nitrogen. The bulb will light as the resis tance decreases.
4. Remove the superconductor from the liquid nitrogen. The bulb will begin dim and eventually go out as the resistance increases.

Caution: This demonstration requires low-resistance contacts to the superconductor.If the switch fails to provide change in light intensity, repeat contact construction as described in the Preparation of the 1-2-3 Superconducting Pellet section. The superconductor may well need an anneal.

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