Concepts

Thermal expansion, electric heating

Overview

When a length of copper or nichrome is heated, it lengthens due to thermal expansion. The wire is suspended between two posts and heated by a variac. A small weighted hook is placed in the middle of the wire to increase visibility of the wire's change in length.

Details

Equipment

• [1] Copper or nichrome wire
  
• [2] Post and socket
  
• [1] Small weight on a hook
• [1] Variac with spare fuses
  
• [1] Slot-head screwdriver
  
• [1] Wire cutter
  
• Extension cord (if necessary)
  

Classroom Assembly

1. Set up the posts and sockets.
   
2. Cut off a couple of metres of wire.
   
3. Secure the wire to the posts.
   
4. Make sure the variac is off.
   
5. Plug the demo into the variac and the variac into mains power.
   

Important Notes

• DO NOT touch the wire. It is HOT both electrically and in temperature.
  
• DO NOT turn the variac on with the voltage turned up to prevent blowing a fuse.
  

Script

1. Set the variac to 0 V.
2. Turn on the variac.
3. Slowly turn up the variac. The wire will heat and begin to expand (sag).
4. Turn the variac to 0 V. The wire should contract and rise.
5. Turn off the variac.
   

Additional Resources