Introduction: (Initial Observation)
Although all metals are good heat conductors, they are not conductive heat at the same rate. Some metals are simply a better heat conductor than others. For safety and energy conservation reasons we my want to use metals that are not good heat conductive. On the other hand for efficient heat transfer from pipes and radiators to the air we may need metals that are very good heat conductors.
Knowing the heat conductivity of different metals can help us in selecting the right metal for different uses.
In this project we will compare different metals to see which one is a better heat conductor.
Adult supervision and help is required in this project
Find out about heat conduction and how it works. Read books, magazines or ask professionals who might know in order to learn about different metals and their physical properties such as conductivity. Keep track of where you got your information from.
In conduction, heat is carried by means of collisions between rapidly moving molecules at the hot end of a body of a matter and the slower molecules at the cold end. Some of the kinetic energy of the fast molecules passes to the slow molecules, and the result of successive collisions is a flow of heat through the body of matter. Solids, liquids, and gases all conduct heat. Conduction is poorest in gases because their molecules are relatively far apart and so interact less frequently than in solids and liquids. Metals are the best conductors of heat because some of their electrons are able to move about relatively freely and can travel past many atoms between collisions.
Some materials conduct heat more efficiently than others. Metals, for example, are good conductors and, therefore, poor insulators. Such substances as wood and cloth are inefficient conductors and , therefore, efficient insulators.
The following situation shows a conductometer with wax attached to the ends. The wax melts and the times for each wax bead to melt is noted below in the table.
Notice that the number associated with thermal conductivity does not have units attached to it. This is simplified to show that this is really Thermal Conductivity of Materials Compared to Air.
The higher the number the better that material is at conducting thermal energy. Therefore copper is the best conductor of thermal energy and steel is the worst conductor of heat energy. Remember that this is only for the materials listed below.
Picture in the right shows a MiniScience conductometer.
|Scientific Name||Chemical Symbol||time (s) to melt||Thermal Conductivity|
|Copper||Cu||106 seconds||16 000 units|
|aluminum||Al||132 seconds||8 600 units|
|brass||Alloy||215 seconds||4 600 units|
|iron||Fe||240 seconds||2 000 units|
|steel||Alloy||242 seconds||2 000 units|
You may also perform heat conductivity experiment using same size metal electrodes.
MiniScience Part# METELECT11
Which metal is the best heat conductor?
This is a sample experiment that we found while gathering information. This method is not recommended for young students.
One method of energy transfer is by conduction. In this experiment you will compare the properties of conduction in different types of metal. To do this similar size rods of different types of metal are heated at one end while the rate of rise in temperature is measured and recorded at the other end.
Following diagram shows the use of temperature probes to measure the temperature, however you can use other types of thermometers or wax to compare the heat conductivity.
- Assemble the apparatus as shown in the diagram. Use insulation tape to fix the temperature probes securely so that the end of each probe is in good contact with the rod. Hold in a boss and stand above the light bulb.
- Use a light bulb to supply heat to the rods. It is important that this bulb is placed centrally so that each rod is heated equally.
- Connect temperature probes to a computer or other recording device.
- Start the device or program to begin logging.
| What are temperature probes?
Temperature probes are electronic components used to measure the temperature. Two main types of temperature probes are Thermocouples and Thermistors.
Thermocouples are components that produce small amounts of electricity when they get hot. More heat, creates more electricity in a thermocouple.
Thermistors are components that change their resistance based on the environments temperature.
Use of thermocouples and thermistors are not suggested to young students who want to do a science project; however, schools, colleges and companies may choose to use them for their accuracy and ability to measure high temperatures.
To purchase thermistors and thermocouples, you may search the Internet.
Thermocouples and thermistors can be connected to computers (via analog-digital converters) to record temperature. For more information about recording software and converters visit www.dataq.com .
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement. Bellow is a sample question/ purpose for this project.
The purpose of this project is to compare the ability of different metals to conduct heat.
I want to test the heat conductivity of some popular metals such as copper, aluminum and steel to see which one is a better heat conductor.
Here are two sample questions for this project:
Which metal conducts heat most efficiently?
Which metal is a better heat conductor?
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
The independent variable (also known as manipulating variable) is the type of metal. Possible values are copper, aluminum and steel. (Type of metal is an independent variable means that we choose the type of metals for our test)
The dependent variable (also known as responding variable) is the time it takes for metal to transfer certain amount of heat to a certain distance. (It depends on the type of metal)
Constants are the dimensions of metals being tested and the test method.
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
In this experiment you will compare the heat conductivity of three different metals. You may do this using samples of different metal rods or a conductometer as shown in the picture.
Go to the hardware store and buy 3 pieces of copper, stainless steel and aluminum bare metal wire. All wires must be the same diameter (3mm or 4mm) and the same length (about 6″ to 8″). Get a package of plain white candles, some matches and a watch with a second hand. Carefully melt some wax from a candle, rolling the warm wax into balls of the same size – about a quarter of an inch in diameter. You may have to increase the diameter of the wax balls, depending on thickness of the thickest wire you were able to find because in the next part of the experiment you’re going to skewer the wax balls on the end of the wires. If your wires are long, carefully measure your different wires into lengths of the same size – 6 inches long would be good – and ask the adult helping you to cut them for you.
Next light a candle and, holding your wire with a wax ball on the end with some tongs, put the end of the wire opposite the wax ball into the candle flame, hold it there until the wax ball melts off the wire and time on the watch how long it takes for the wax ball to melt off. Carefully note on a data collection sheet, for each piece of wire: whether it was copper, aluminum or stainless steel, how thick it was, how long the piece was and how long it took for the wax to melt off it.
If you are using a conductometer, hold the center of the conductometer over the flame.
Summarize your results and compare them with your hypothesis – did the wax ball fall off the copper wire fastest?
Extended optional procedure:
If you can get wires with different thickness from the same metal, you can also use the same procedure to test the effect of thickness on heat transfer or conductivity. Try to find out what effect did the differing thickness’ of the wire have on the melting time? Write up your results and comparison of results with the hypothesis in a conclusion either supporting or disproving your hypothesis.
In this experiment we will test the heat conductivity of 3 different spoons. You may select spoons made of stainless steel, aluminum and copper. You may also use this method to compare the heat conductivity of metal strips, rods or pipes.
- Press a small piece of warm candle wax from Part I into the handle of each of the three spoons (see diagram). Push the quarters into the wax so that they are attached to the spoons.
- Fill the beaker with 300 mL water and place the beaker on a hot plate.
- Place the three spoons in the water so that the quarters come out of the top of the beaker.
- Turn on the hot plate and allow the water to warm. Observe the quarters and note the order in which they fall from the spoons.
More advanced experiment
Jut for your review
Six rods of identical size, but made of different materials, are covered with heat-sensitive paint. One end of each rod is inserted into a pipe through which steam can pass. Thermal conductivity of each rod is indicated qualitatively by the extent of the color change. (The rods are made of copper, aluminum, zinc, tin, Iron and lead).
Directions: Wait until the water is almost boiling before attaching the hose to the end of the pipe. (Wear hand protection in case steam begins to emerge prematurely.) Point out the different color change rates as the process continues.
Applications: Conduction rates determine often what materials are used as insulators.
Materials and Equipment:
List of material can be extracted from the experiment section and varies based on your final experiment design. Following is a sample list of material.
Material needed for this project may be purchased online from MiniScience.com, klk.com or scienceprojectstore.com.
If you have a scientific supplier in your area, you may also be able to buy them locally.
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
Your experiment, results are in the form of a table or graph.
For this experiment results must have answer to these questions.
|Type of Metal||Minutes took for the wax to melt|
Make a graph:
Use the above results table to make a bar graph. Use one vertical bar for each metal you test. The height of each bar will represent the minutes it took for the wax to melt. The shorter the bar the more conductive the metal is. On or under each bar write the name of the metal it represents.
For this experiment, result may be the answers to the following questions.
1. In what order did the quarters fall from the spoons? Explain this based on heat conductivity.
2. Identify and explain a kitchen item made of each plastic, metal and wood. Distinguish the uses of these items based on heat conductivity.
3. Explain energy transfer through heat conductivity in your own words.
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Of copper, stainless steel and aluminum wire, ……….. conducts heat the best. …………… is the second best conductive and …………… has the lowest conductivity.
After you write the conclusion, write some additional information to show that you really learned the subject. This is an example:
Some materials are naturally good conductors of heat, while others are poor. Metals usually conduct heat extremely well, which explains the use of iron and copper in cooking utensils. Materials such as plastic, glass or wood do not conduct well; therefore, it is a better idea to use a wooden spoon than a metal spoon when cooking.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.