Objective:
– To show how resistance of an electrical conductor will increase with an increase of temperature.
Apparatus:
- Resistance demonstrator
- Power supply (Circuit-Test PSB-330T)
- Propane gas tank, with valve and hose
- Large Analog Ammeter, 0-2 Amp DC (Triplett 726)
Method:
The resistance wire coil (mounted above a burner) is connected in series with the Ammeter and Power supply. While the coil is cold, current is adjusted to 1.7 Amps. See preferred settings below. When the burner is ignited, current flow will rapidly drop to approximately 40% of full scale, due to increased resistance of the wire coil at a higher temperature.
Note:
Do not attempt to use a lamp as an indicator of current. (A lamp filament behaves like a negative resistance as voltage decreases, masking the desired effect).
Settings:
On the Power Supply, Master V= 1.6v, A=1.71 amp, and on the large analog ammeter, A=400 mA.