Monday, 22 July 2013 09:49

## I1-13 THERMAL EXPANSION - BIMETAL STRIP

• ID Code: I1-13
• Purpose: Demonstrates differential thermal expansion
• Description:

Two strips of different metals, invar steel and brass, are welded together to form a bimetal strip. Since each metal has a different coefficient of thermal expansion, heating the bimetal strip will result in the metals expanding at different rates, causing it to bend.

When heating, always wear goggles and handle the flame with care, ensuring that it is not pointed near students or flammable materials. Use in a well ventilated classroom.

##### Engagement Suggestion
Ask your students: • Which metal will expand more when it is heated, and why?
• What happens when it is cooled?
• How could you make use of this to measure or control something?
##### Background

The amount a metal expands or contracts with temperature is governed by its coefficient of thermal expansion, a property which varies between different metals depending on their molecular structure. Invar steel is an alloy designed to have an exceptionally low coefficient, about one-tenth that of most steel, while brass has a higher coefficient than even ordinary steel. So the brass expands much more rapidly than the steel does when heated.

Bimetallic strips like this are used in some types of thermometers and thermostatic controllers (including many older window thermometers and household thermostats). Check out demonstrations I1-17 and I1-18 for examples and to see how this works.

• Availability: Available
• Loc codes: I1, I0
• #### I1-01: THERMOMETERS

Show several types of thermometers. Read More

• #### I1-13 THERMAL EXPANSION - BIMETAL STRIP

Demonstrate differential thermal expansion. Read More
• #### I1-14: THERMAL EXPANSION OF ALUMINUM - OPTICAL LEVER

Demonstrate thermal expansion in a complicated way. Read More
• #### I1-15: THERMAL EXPANSION - PIN BREAKER

Demonstrate thermal expansion in a dramatic way. Read More
• #### I1-16: THERMAL CONTRACTION OF CUPS WITH LN

Measure coefficients of linear expansion. Read More
• #### I1-17: THERMOSTAT - MODEL

Model of use of a bimetal strip in a thermostat. Read More
• #### I1-18: BIMETALLIC STRIP THERMOMETERS

Allow students to see how bimetallic strips are used in thermometers and thermostats. Read More
• #### I1-19: LAVA LAMP

Demonstrate differential thermal expansion between two liquids, and to take us all back to the 1960s. Read More
• #### I1-21: WATER NEAR 4 DEGREES CELCIUS

Demonstrate that the maximum density of water occurs around 4 degrees centigrade. Read More
• #### I1-22: WATER DENSITY VS TEMPERATURE

Demonstrate the change in the density of water with temperature. Read More
• #### I1-32: RUBBER BAND CONTRACTION DURING HEATING

To demonstrate that rubber contracts when heated. Read More
• #### I1-40: REVERSIBLE THERMOELECTRIC DEMONSTRATOR

Demonstrate thermoelectric power generation or how thermoelectric devices can create hot and cold regions. Read More
• #### I1-41: THERMOELECTRIC MAGNET

Demonstrate production and use of thermoelectric current. Read More
• #### I1-42: THERMOELECTRIC FAN

Illustrate generation and use of thermoelectric current. Read More
• #### I1-51: RUBBER AT LN TEMPERATURE

Demonstrate how a normally elastic material at room temperature becomes rigid at very low temperatures. Read More
• #### I1-52: TUNING FORK AT LIQUID NITROGEN TEMPERATURE

Demonstrate the change in frequency of a tuning fork at liquid nitrogen temperature. Read More
• #### I1-53: LEAD BELL AT LIQUID NITROGEN TEMPERATURE

Demonstrate the effect of temperature on vibrations in a lead bell. Read More
• #### I1-61: DUST EXPLOSION

Produce a dust explosion. Read More
• #### I1-62: DUST EXPLOSION MODEL

Show why small particles of flammable material can create a dust explosion when ignited. Read More
• #### I1-63: HYDROGEN EXPLOSION

Produce a hydrogen explosion. Read More