How Temperature Affects Carbon Resistors

Overview

Objectives/Goals Determine how temperature affects carbon resistors' resistance. Preliminary research showed that resistance is directly proportional to temperature, R=R(ref){1+a[T-T(ref)]}, where a is the temperature coefficient of resistance. Methods/Materials For five 100 Ohm, 1/4 W resistors, measured each resistor's resistance [R(ref)] at room temperature [T(ref)] and resistance [R] at temperatures [T] of -198, -60, 23.6 (Room Temperature) 50, 100, 150, 200 and 250 degrees C. Results My average measured resistance at temperatures -198, -60, 23.6, 50, 100, 150, 200 and 250 degrees C were 103.88, 99.34, 98.26, 97.32 96.1, 95.3, 94.425, and 93.9 Ohms, respectively. I fit this data by use of least squares fit to R=-0.02T+98.74. From the slope, -0.02, determined the temperature coefficient of resistance to be -0.0002 /C. Conclusions/Discussion Data didn't support hypothesis - resistance increased as temperature decreased. Further research showed this as typical for carbon - a semiconductor. Semiconductors have an energy gap between the valence and conductive bands. Heating carbon introduces more electrons in the conductive band decreasing resistance; cooling forces the electrons from the conductive band down to the valence band, increasing resistance. Semiconductor resistors have a negative temperature coefficient of resistance, metal resistors - positive.

Competition history

• CSEF 2006 Electricity & Electronics · Entry J0701

Resources

• CSEF project summary ↗

Related projects

Closest projects by meaning, across every fair and year in the corpus.

Browse more like this

• All Physics and Astronomy projects
• CSEF Physics and Astronomy projects
• Every CSEF 2006 project