Resistors At Ln Temperature - Light Bulb Indicator

Purpose

To demonstrate materials with both positive and negative temperature coefficients of resistance.
 

Equipment

Carbon and copper resistors, mounted light bulb, and liquid nitrogen.

 

Setup Time

5 min.
 

    Images

    k5-36

    Description

    Copper and carbon resistors are mounted on plastic tubes so that they can be inserted into liquid nitrogen. When the copper resistor is wired in series with a light bulb across 110 VAC the bulb becomes brighter when the resistor is cooled to the temperature of liquid nitrogen, indicating a positive temperature coefficient of resistance for copper. When the carbon resistor is wired in series with the light bulb across 110 VAC the bulb becomes dimmer when the resistor is cooled to the temperature of liquid nitrogen, indicating a negative temperature coefficient of resistance for carbon. ◙