Hello Michelle: Pure metals such as silver, copper and aluminum have a positive coefficient of resistance versus temperature meaning that as the temperature of the conductor increases so does the resistance. Your wire samples must be physically the same to perform the experiment you described. Notice that the change in resistance of a piece of wire is not very large requiring sensitive equipment to be used in the demonstration. Take two cheap Radio Shack resistors of equal value, for example, 1000 ohms each, connect them in series to a 6-volt battery. Each will drop of 3 volts more or less because of the resistance tolerances. After taking the room temperature reading across one with a voltmeter, apply warm air from a hair dryer. As the resistor gets hot, the voltage across it will rise indicating the resistance value increases. Be sure you have good connections between the resistors and the battery as well. The voltage change will not be dramatic. Look-up this reference on the Internet: http://www.tpub.com/neets/book4/11e.htm Your MAD.SCI Micro.
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