I-V characteristics lab
Probe metal, filament-lamp and diode I–V graphs to compare resistance, temperature effects and conduction direction.
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Learning goals
- State resistance as potential difference divided by current
- Apply resistance equals potential difference divided by current
- Describe the effect of temperature on metallic resistance
- Sketch and interpret required current–voltage characteristics
Testing a fixed 20 ohm resistor with a 2.0 volt supply. The voltmeter reads 1.99 volts and the ammeter 99.7 milliamperes.
- p.d. across it, V
- 1.99 V
- Current, I
- 0.0997 A
- Resistance, V / I
- 20.0 Ω
Try this
0 of 4 doneRecord at least five readings for the fixed resistor, from 0 V to at least 5 V. (not done yet)
The points lie on a straight line through the origin: I is proportional to V, so the resistance is constant (ohmic).
Do the same for the filament lamp and compare the two graphs. (not done yet)
The curve bends towards the V-axis: as the filament heats up its resistance rises, so each extra volt adds less current.
Test the diode in both directions, including readings above 0.6 V forwards. (not done yet)
A diode conducts in one direction only, and only once the forward p.d. passes about 0.7 V. In reverse its resistance is very large.
Record the thermistor at the same supply p.d. at 20 °C and at 80 °C. (not done yet)
The hotter thermistor carries more current at the same p.d.: an NTC thermistor's resistance falls as its temperature rises.
You’ve tried every task.
Your readings
| # | V / V | I / mA | Remove |
|---|---|---|---|
| No readings yet. Set up a measurement, then record it. | |||