5D20.10 Wire Coil in Liquid Nitrogen


Temperature-dependent resistivity of copper


A copper coil is connected in series with a flashlight. When the coil is cooled in liquid nitrogen, the resistance drops and the flashlight bulb glows brighter. The resistivity of copper is temperature-dependent, with its resistance about 2 times greater at room temperature (293 K) than at liquid nitrogen temperature (77 K). 



  • [1] Copper coil wrapped around acrylic rod and connected to a flashlight
  • [1] Small dewar
  • [1] Small dewar holder
  • Liquid nitrogen

Safety Equipment

  • [2] Safety glove
  • [1] Safety glasses

Classroom Assembly

  1. Place the dewar in its holder.

Important Notes

  • Wear safety gloves and glasses to avoid direct contact with liquid nitrogen. Liquid nitrogen can cause severe burns and blindness. Use with caution.
  • The bulb may glow dimly at room temperature if the batteries in the flashlight are new.
  • The coil warms quickly when removed from the liquid nitrogen. The bulb brightness decreases rapidly as the coil warms.


  1. Put on safety gloves and glasses.
  2. Dim the room lights.
  3. Turn on the flashlight.
  4. Notice the flashlight is dim.
  5. Submerge the coil in liquid nitrogen.
  6. Point out that the flashlight lights up and grows brighter as the temperature of the coil decreases.
  7. Turn off the flashlight.


Additional Resources


  • PIRA 5D20.10
  • Video encyclopedia 17-21


  • Don't attempt this at home!

Last revised

  • 2020


  • Original construction: a standard flashlight was modified by soldering the flashlight bulb in series with a coil of wire. The coil consists of many turns of 24-gauge copper wire. When constructing, add turns to the coil until the flashlight does not light up at room temperature.

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If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.