Thermal Conductivity Rod (Randy Daniels)
Author
Randy Daniels, Science Teacher, Hillside Middle School, Simi Valley, CA.
Principles
Heat Transfer. Heat is defined as the average kinetic energy of the molecules that an object has. There are three ways that heat can travel: Radiation, Conduction, and Convection. This piece of equipment can be used to demonstrate how heat is conducted through a solid object.
Standards MS-PS1-4
Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed. [Clarification Statement: Emphasis is on qualitative molecular-level models of solids, liquids, and gases to show that adding or removing thermal energy increases or decreases kinetic energy of the particles until a change of state occurs. Examples of models could include drawing and diagrams. Examples of particles could include molecules or inert atoms. Examples of pure substances could include water, carbon dioxide, and helium.]
Materials needed
1. Thermal Conductivity Rod
2. Lighter (or a candle can be used)
3. Wax (or you can use the heads of match sticks)
Procedure
First, find a way to secure the Thermal Conductivity Rod. This can be done using a vertical clamp stand, or you can construct a makeshift stand by securing the handle of the rod on to a flat surface (such as a chair)with enough tape to hold it in place. The handle of the rod could be fixed into place on a chair, with the conductivity rods hanging off of the edge.
Next, place a dab of wax on the end of each of the conductivity rods.
Place a lighter, or perhaps a candle, under the center hub where each of the conductivity rods connect. Keep the flame in place until the wax on the end of the conductivity rods begin to melt. Take note of which dab of wax melted first, being sure to note which type of metal upon which the wax was resting.
Explanation
Heat can be transferred by radiation, conduction, or convection. With this equipment, one can demonstrate the method of heat transfer through conduction. As a solid object heats up and the average kinetic energy of the rods increases, the heat energy moves along each of the metal rods. This occurs due to the increasing kinetic energy of the molecules which causes them to collide with one another at a faster rate. This heat energy travels along the length of each rod, molecule by molecule, until the heat energy reaches the wax, which, in turn, is conducted through the wax, causing the wax to melt.
Questions
Which type of metal appears to conduct heat the best? It appears that Copper (Cu) is the best conductor of heat.
What evidence can you state to support your answer? The wax on the copper rod melted the quickest (1:29), which would indicate that, of the different types of rods, copper is the best conductor of heat.
Would the color of the flame have an affect on the rate of heat transfer? Since blue flames are generally thought to be hotter than orange flames (the blue color is actually due to chemiluminescence, not a direct result of heat), it would make sense that, because blue flames have higher temperatures (Note: temperature and heat are not the same thing), the rate of conduction would, in fact, be increased.
Everyday examples of the principles illustrated
Everyday examples of how heat is conducted include:
a frying pan placed over a flame (the heat from the flame is conducted through the bottom of the pan and, eventually, the rest of the pan.
Boiling water in a pot (heat from the bottom of the pan is conducted through the water, continuing to increase the water's temperature until it boils.
A spoon sitting in a hot cup of tea. The heat energy from the hot tea is transferred to the spoon, which, in turn gets transferred to a fingers when touched.
Photos
