Liquid Nitrogen

Liquid nitrogen is poured like water to cool an electronic device to a temperature of 77 K (-196° C/ -323° F). Liquid nitrogen is produced by liquefying air and is widely used as an inexpensive cryogenic refrigerant. It can be stored for long periods in special containers called Dewar flasks, named after Sir James Dewar, the British scientist who first liquefied hydrogen in 1898. Liquid nitrogen has many everyday uses ranging from the production of frozen foods to the removal of warts. Sperm banks use liquid nitrogen to preserve genetic material. Research laboratories commonly use this versatile refrigerant to trap volatile materials. Cooling in liquid nitrogen is often a starting point for reaching even lower temperatures using liquid helium.

 

Magnetic Levitation above a Superconductor

A small cylindrical magnet floats above a high temperature superconductor. The vapor is from boiling liquid nitrogen, which keeps the superconductor in a zero-resistance state. As the magnet is lowered toward the superconductor, it induces an electric current, which creates an opposing magnetic field in accordance with Ampere's law. Because the superconductor has no electrical resistance, this induced current continues to flow, keeping the magnet suspended indefinitely.