Description: A length of iron wire shows a sudden reduction in length on heating through the bcc-fcc phase transition.

A length of iron music wire is suspended between two poles and a current is passed through it. The wire sags as it is heated but there is an abrupt decrease in the length on heating through the transition temperature which manifests itself as a 'jump' in the wire. The transition may be seen more clearly 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.

The iron wire is plugged into a variac. Typically 70 or so volts is required. DO NOT turn the variac on with the voltage turned up - you will blow a fuse. DO NOT touch the wire - it is HOT both electrically and in temperature.

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

Cautions: DO NOT turn the variac on with the voltage turned up - you will blow a fuse. DO NOT touch the wire - it is HOT both electrically and in temperature.

Concepts demonstrated: thermal expansion, solid-solid phase transition

Setup Time: Short

Difficulty/Commitment: Straightforward

Visibility:

References: PIRA 4C45.10