Resistance, Temperature, and Ohm's Law (Demo)
Obj:  Determine relationship between R and T in conductive materials, and verify Ohm's Law

Materials:  tungsten, carbon, & Nichrome filaments, AC voltage source, voltmeter, ammeter
Methods and Analysis:
1.  Record the filament's original cold resistance (R_o) in Ω's using the 1000 Ohm setting on the multimeter.
2.  Record V and I at 10V steps between 40V and 100V for all three filaments.
3.  Construct a V I R P table for each filament.  Power indicates heat energy in J/s.
4.  Plot R (y-axis) vs. P for all three filaments on one graph.  Explain the results.  Which filament is most powerful?  What is unique about the carbon filament?
5.  Compute for each filament a percent change in R.   [% change  = (Δ R / R_o) X 100%]
6.  Plot V vs. I for all three filaments on one graph.  Determine the slopes.  What do the slopes represent.  Compare the three filaments and their slopes.   Do the three filaments follow Ohm's Law?   What is a true ohmic material?
7.  Why is tungsten a good material for a light bulb, and nichrome for a toaster?
8.  What are the advantages of fluorescent and LED lights?

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