4C45.10 Iron Wire

Concepts

Thermal expansion, solid-solid phase transition

Overview

When a length of iron wire is heated, it shows a sudden reduction in length through the bcc-fcc phase transition. The iron wire is heated by means of a variac. The wire is suspended between two posts and the posts are connected across the variac. A small weight on a hook is placed in the middle of the wire to increase the visibility of the sudden length reduction. Note: this demonstration requires a video camera to be clearly visible in large lecture halls.

Details

Equipment

  • [1] Iron wire
  • [2] Posts and sockets
  • [1] Small weight on a hook
  • [1] Variac with spare fuses
  • [1] Screwdriver
  • [1] Extension cord

Important Notes

  • The transition is more visible on cooling where a sudden drop in the wire is observed. Leave the wire at a high temperature for a few seconds to allow the entire length of the wire to heat up.
  • DO NOT turn the variac on with the voltage turned up to prevent blowing a fuse.
  • DO NOT touch the wire - it is HOT both electrically and in temperature.

Script

  1. Set the variac to 0 V.
  2. Turn on the variac.
  3. Slowly turn up the variac to about 70 V. The wire will heat and begin to expand (sag). When the wire passes through the bcc-fcc phase transition, it will suddenly contract and 'jump' up.

 

Additional Resources

References

  • PIRA 4C45.10

Disclaimer

  • Don't attempt this at home!

Last revised

  • 2018

Technicals

  • We use Royal Brand Music Spring Wire, Music wire gauge No 12, 0.029 inches diameter.
  • Eight turns off the roll is about right.

Related AV

Related demos

 

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.