As the temperature of the wire decreases, so does the resistance.

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Teachable Topics:

• electricity
• resistance
• electron band structure

Theory:

Atoms are always vibrating. How much they vibrate and move depends on, among other things, temperature. At high temperatures, atoms will vibrate more vigorously than they would at room temperature. Conversely, atoms vibrate less at colder temperatures. In a conductor like copper, these vibrations can cause resistance for flowing electrons. The more vibration, the harder it is for the electrons to pass through the material without running into the vibrating atoms.

Picture a blindfolded shepherd trying to walk through a herd of sheep. If the sheep are all quickly moving around in the herd, chances are the shepherd will run into a few or have to change his path a couple times to get through the herd. If all the sheep are still, the shepherd should have an easier time walking through the herd. There was less "resistance" for the farmer because the sheep were not getting in his way. This is why when we immersed the copper coil in the liquid nitrogen, the resistance of the coil went down. The atoms started to vibrate less and less because of the cold temperatures, and so there was less resistance for the electrons passing through it.

Apparatus:

• 100 ft of magnet wire
• Rod
• Liquid Nitrogen
• Ohmmeter
• Gloves
• Safety Glasses

Procedure:

1. Coil the wire around the rod in as short a length as possible, leaving the ends long enough to hook up to the multimeter.
2. Hook the coil up to the ohmmeter, and turn it on, setting it to measure resistance.
3. Submerge the coil into the liquid nitrogen and watch as the resistance shown on the ohmmeter goes down. The resistance will increase when the coil is taken out and the temperature starts to return to normal.

Safety:

• Be very careful when using liquid nitrogen, wear safety goggles and cryogenic gloves.