Thermal conductivity of Wood and Metal

Boiling water in a paper cup

Relevant Resource questions :

Concepts demonstrated :

• heat flow along a copper rod
• heat flow through two different connected bars (copper and stainless steel)
• temperature gradient
• thermal conductivity

Equipment needed :

• Copper bar, 22cm long, connected to two beakers with thermocouples attached along the bars length.
• Bar (half copper and half stainless steel) connected to two beakers with thermocouples attached along the bars length.
• Stand for either bar.
• Insulation for either bar.
• Datataker - DT100
• PC computer with serial port.
• Program dtaker.exe (pascal program using Muppet utilities)
• Bunsen burner and matches
• Liquid nitrogen or ice water
• CCD camera and projection equipment (to ensure that the experiment can be seen in a large lecture theatre).
• Computer program bar.exe which simulates heat flow along a bar (pascal program using Muppet utilities).

• Place bar on stand and connect thermocouples to sockets 1 and 4 of the datataker.
• Connect datataker output to the serial port of the PC computer.
• Place a bunsen burner under one of the beakers half filled with water. Place ice water or liquid nitrogen (T=77K or -196 deg C) in the other beaker. You may see localised boiling for the liquid nitrogen where the beaker joins the rod.
• Run the program dtaker.exe (see separate instructions to run the program).
• Experiment with variations on the above by using fluids at different temperatures and with insulating or not insulating the rod.

• Student handout for use in lectures for POE demonstration.
• A Lecturer's outline showing one possible way of using the demonstration interactively in a lecture.

Heat flows from the hot beaker to the cold beaker. This can be shown by displaying the temperature along the length of rod with time. After a period of time an steady state situation will be reached where the temperature across the copper remains fixed. If the bar is insulated this temperature should drop uniformly from the hot end to the cold end. If the bar is uninsulated the temperature may drop exponentially (or something similar to this).

How to use the Demonstration :

• Use it in lectures when talking about temperature gradients, heat flow of steady state situations.
• Allow up to 20 minutes in a lecture to complete the demonstration.
• Use it in tutorials by allowing the students to perform the experiment themselves.
• Examine the variation in temperature along a bar for a steady state situation - bar insulated.
• Examine the variation in temperature along a bar for a steady state situation - bar ininsulated.
• Examine the temperature variation at a discontinuity - join between copper and stainless steel.
• Examine different thermal conductivities for different materials.
• Examine transient effects - change of temperature with time at a particular point along the bar.

• Saucepan handles made of materials other than metal.
• The use of wooden spoons for cooking.
• Temperature gradient through a brick wall of a house.

• Replace program dtaker.exe with Excel so that the acquisition and display of data are portable across computers. Serial interfacing and graphing routines will need to be sorted out.
• Thermocouples may need to be calibrated however when tested they all appear accurate to within a degree (see the CRC handbook (ref 541.9 2/10 in Physics Library pp E107-110)).
• Run a computer simulation (bar.exe) of heat flow and compare to the results in the experiment.
• Start with both beakers at 0 deg C and boil one of the beakers. Perhaps both with ice in them as well.

• This demonstration is suitable for use both in lectures and interactive tutorials.
• This demonstration may be used to engage the students interactively through POEs.
• The datataker manual provides information on how to use the datataker and about thermocouples.