Experimental
1. Locate a variable resistor or a “rheostat” (left picture). Its
resistance can be adjusted between 0 - 100. Adjust to
the highest R.
2. Adjust the output voltage of a DC power supply to 9.0 V.
Connect to the preset rheostat and record the flowing
current I and also the nominal voltage (VR).
3. Slightly decrease the resistance of the rheostat and read
the V and I values. Repeat until the resistance is
minimum.
4. Construct an I-V curve using the data obtained. Voltage
should be assigned on the y-axis.
5. Replace the DC power supply with another power source
e.g. a 9V battery or a solar cell. However, remember to
record the OCV from the battery or from the solar cell
first before connecting with the rheostat.
6. Repeat step 3 – 4. Compare the I-V curves.
7. Determine the maximum power output from each power
source by construction of the P-V curve (P = IxV).
Rheostat (Variable R) Various Power Sources
Question:
1) What controls the maximum power output of each power
source?
2) How to increase the power output of a power source if it
does not provide sufficient power for a device?