Determine the composition of a mystery object via its resistivity (and other properties).
This project may be done by teams of 1-2 individuals. The idea is the measure the resistivity of a mystery object, then compare your value to those for various materials. You can find a small table of resistivities in your textbook -- I can point out larger tables in the library. By comparing your measurement to values in a table, you can guess the composition of the mystery object, under the assumption that it is made of a pure element.
I have a single set of equipment -- voltmeter, ammeter, electric wires, power supply, etc. -- in my office. You may check it out at your convenience for a maximum of two hours. I'll also give you mystery object, which is a very rough cube. Using the equipment, you may measure the relationship between voltage and current through the mystery object, and thus determine the resistance. Make sure you include an estimate of the uncertainty in your measurement.
You'll also need to measure precisely the size of the mystery object. The vernier caliper in the kit will provide a rough value for the length of the object in each dimension. You may approximate it to be a simple box. Again, note the uncertainties in all dimensions.
With measurements of size and resistance, you can calculate the resistivity. Try to estimate the uncertainty in your value. Compare it to values in a table, and guess the composition of the mystery object.
If you wish, you may also measure the density of the mystery object. You can calculate its volume from your measurements of its size. By measuring its mass, too, you can derive its density. Express the density in grams per cubic centimeter. Compare your value against those in a table of the density of pure elements.
Submit a report which contains a diagram of the circuit(s) you used in your experiment, and your guess to the object's identity. You may also include interesting items you discovered during the course of the procedure.
This page maintained by Michael Richmond. Last modified Jan 8, 2003.
Copyright © Michael Richmond. This work is licensed under a Creative Commons License.