Thermal Conductivity of Metals: Which Metal Is the Best Conductor of Heat?
Have you ever touched something that became hot enough to burn you only moments after it was cool to the touch? This can happen when you stir a pot of soup on the stove with a metal spoon or roast marshmallows over a fire with a metal rod. So what explains why it’s a better idea to stir your soup with a wooden spoon and roast your marshmallows with a wooden stick? Objects made of metal can quickly conduct unwanted heat right up to our hands!
So what is conduction, anyway? Conduction is heat moving from one object to another through contact. When heated, molecules in an object begin to shake and move. They also shake and move their neighbors, and the more molecules shaking, the more heat transfer happens. A good example would be roasting a marshmallow on a coat hanger or metal rod. As one end of the rod gains heat from the fire, the rest of the rod gradually heats up as well. Eventually, the whole rod becomes too hot to touch!
Which metal is the best conductor of heat: copper, steel, or brass? Why? After doing some online research, formulate your hypothesis.
- 3 12-inch long metal rods or thick wire: copper, steel, brass, or other metal. Make sure all the wires are the same gauge, or thickness. Why do you making sure the gauge is the same might be an important step?
- 8 identical Styrofoam cups
- Something to boil water in (a pot or kettle)
- 4 instant digital thermometers
- Pitcher or other large container that will fit in the refrigerator
- Notebook and pen
- Fill a pitcher or other large container with water and ice cubes. Allow the water in the pitcher to cool for at least half an hour.
- Bend each metal rod in half two times to make metal bridges. Why do you think we should fold the rod in half twice? Would folding it once produce the same results?
- Place the cups in pairs. Three bridges of the same metal go between each cup. One pair of cups will have no bridges. This is the control group.
- Place the instant digital thermometers in each of the cups that will hold cold water.
- Have an adult boil some water. Let it cool a bit before use.
- For each pair of cups, pour equal volumes for hot water into the “hot” cup. Be sure the water covers the ends of the bridges.
- For each pair of cups, pour equal volumes of cold water into the “cold” cup. Be sure the water covers the end of the bridges. Why do you think the volumes of water need to be equal?
- Take the initial temperature of the cold water. Record the temperature in a chart listing the time (in minutes) and temperature (in degrees Fahrenheit).
- Record the temperature of each cold water cup every 5 minutes for a total of 30 minutes. Your table should have which set it is (none, copper, steel, brass), time, and boxes to fill in for temperature. Do you think that all of the heat that’s conducted away from the hot cup goes into the cold cup? Why or why not? Hint: sometimes heat doesn’t always go where we want it to!
- Which cup of cold water experienced the greatest change in temperature from the beginning to the end? Calculate this by subtracting the cup’s starting temperature from its final temperature.
- Organize your data with line graphs. On the x-axis, plot time in minutes. On the y-axis, plot temperature difference in degrees. By creating a chart like this, we can see which metal transfers the most heat overall. This also gives us some information about each metal’s conductivity: The steeper the slope, the higher the conductivity.