Re: [Phys-l] light bulbs

[DMathies@tulsacc.edu]

One of our instructors does this experiment with a tungsten filament lamp 
then a carbon filament lamp plotting V vs I gives a fairly linear curve in 
the range of 30 to 110 V. The range 0 to 30 is not linear. Did not go 
above 120 V because the filaments burn out.  Using the measured resistance 
of the tungsten lamp at 20 Celsius and the calculated resistance when at 
110 V you get a temperature of 2631 degrees Celsius at 110.

Typical Data for tungsten with a measured resistance of 29 ohms at 20 
degrees Celsius:

V (V)   I (A) 
10      .12
20      .15
30      .178
40      .198
50      .21
60      .22
70      .24
80      .26
90      .277
100     .29
110     .306
120     .32

Typical Data for carbon with a measured resistance of 260 ohms at 20 
degrees Celsius:

V (V)   I (A)
10      0
20      .1
30      .18
40      .25
50      .33
60      .40
70      .48
80      .58
90      .68
100     .78
110     .89
120     1.0

Don Mathieson
Tulsa Community College
dmathies@tulsacc.edu