60. Fun With LN2

In order to get liquid nitrogen we need a little extra notice. Some experiments are:

  1. Flowers can be frozen brittle or fruit frozen solid so they will shatter when dropped. Another good demonstration is to bounce a racquetball and then use liquid nitrogen to freeze it and shatter it.
  2. Balloons of air can be completely deflated and thrown on the floor to reinflate. If helium-filled balloons are used, their volume will be reduced to about one quarter. They are now denser than air and will drop to the floor, rising to the ceiling after a few minutes as they warm up.
  3. You can plunge your hand into the liquid nitrogen for an instant. The Leidenfrost effect (vapor barrier) protects your hand.
  4. A piece of the new high temperature superconductors will float a small magnet demonstrating the Meissner effect after cooling in LN2. We also have a highly pinning superconductor which will float over a magnet track, or even under the magnet track
  5. Liquid nitrogen can be shown to freeze when the air is pumped out of a glass chamber as depicted in the video below.
  6. The temperature coefficient of resistance can be investigated with a copper wirewound resistor and a carbon resistor. A small circuit with a battery, lightbulb and resistor is set up and then the resistor is put into a cup of liquid nitrogen. The change light brightness indicates the sign of the temperature dependence. The temperature dependence of a semiconductor can be investigated by dipping a large green LED into liquid nitrogen and noting the color change.
  7. Ice Cream Recipe
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Gas In atmosphere Boiling point Melting
Nitrogen 78.1% 77 K, -196 C, -320 F 63 K
Oxygen 20.9% 90 K, -183 C, -297 F 54 K
Argon 0.9% 87 K, -186 C, -303 F 84 K
Carbon Dioxide 0.038% 195 K,-78 C, -108 F none
Helium none 4.2 K, -269 C, -452F 0.95 K
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