For a certain resistor, the value of its resistance does not change appreciably. However, for a light bulb, the resistance of the filament will change as it heats up and cools down. At high AC frequencies, the filament doesn’t have time to cool down, so it remains at a nearly constant temperature and the resistance stays relatively constant. At low AC frequencies (e.g., less than one hertz), the filament has time to change temperature. As a consequence, the resistance of the filament changes dramatically and the resulting change in current through the filament is interesting to watch.
In the first part of this activity, investigate the relationship between current and voltage in simple ten-ohm (Ω) and one-hundred ohm resistors. In the second part, investigate the relationship between current and voltage in the filament of a small light bulb. Setup 1. Set up the PASCO 750 Interface and the computer and start Data Studio. 2. Connect banana plug patch cords into the ‘OUTPUT’ ports on the interface. 3. Open the DataStudio file:02Ohm’s Law.ds The file opens with a Signal Generator window and a Scope display of voltage. The Scope display will show the voltage across the resistor from the ‘Output’ of the interface and the output current from the interface through the resistor. The Signal Generator is set to produce a triangle wave at 60 Hz. It is set to ‘Auto’ so it will automatically start or stop the signal when you start or stop measuring data. DataStudio will record the ‘Output Voltage’ and the ‘Output Current’. 4. Place a ten-ohm (Ω) resistor in the pair of component springs nearest to the banana jacks at the lower right corner of the AC/DC Electronics Lab Board.