Variable DC supply
Apply 1–10 V across the resistor with the circuit switched off while wiring.
Physics / Ohm’s law
FREE TO EXPLOREEXPERIMENT 07 · PHYSICS LABORATORY
Ohm’s law and resistance from a current–voltage graph
Determine the resistance of an ohmic conductor from the gradient of current against potential difference. Explore a virtual apparatus, collect readings and analyse a graph.
CHANGE · OBSERVE · MEASURE
Your virtual workbench.
CURRENT I—
MEASUREMENT STATUS
Ready for a virtual observation.
Adjust the apparatus, then take a reading.
Readings are generated by an ideal model. The diagram is schematic and is not to scale.
Simulation assumptions and limits
This model assumes a constant 100 Ω resistance, exact applied voltage, an ideal ammeter and voltmeter, and no heating or lead resistance. Current is rounded to 0.01 mA. The chosen voltage grid can give perfectly collinear readings; a zero fit-only standard error is not a claim of zero laboratory uncertainty. The generator uses I = V/100 and displays current in mA. Graph fitting converts current back to A and estimates R = 1/gradient. The supplied 100 Ω value is a model reference, not an independently measured result.
Know your apparatus.
100 Ω model resistor
Provide a constant resistance for the simulated comparison. A physical resistor must have an appropriate power rating.
Ammeter and voltmeter
Place the ammeter in series and the voltmeter in parallel across the resistor.
Switch and leads
Complete secure connections and limit unnecessary heating between readings.
FOLLOW THE METHOD
A reason behind every step.
Determine the resistance of an ohmic conductor from the gradient of current against potential difference. Suggested independent settings: 1, 3, 5, 7, 9 V.
Identify the circuit
With the supply off, connect the resistor and ammeter in series and the voltmeter across the resistor. Check polarity and meter ranges.
Why this step matters
Correct topology ensures the two meters describe the same element.
Choose a safe operating range
Begin at low voltage. For real apparatus check power rating and current limit before using the full range; keep temperature stable.
Why this step matters
Heating can alter resistance and excessive power can damage a resistor.
Measure a voltage-current pair
Set the voltage and obtain the current. Record voltage in V and the displayed current in mA, including the display resolution.
Why this step matters
A pair must refer to the same steady operating condition.
Collect a spread of observations
Take at least five voltage settings across the permitted range. Repeat if possible and compare increasing and decreasing voltage runs in a physical experiment.
Why this step matters
A broad spread constrains the gradient; repeated or reversed runs can reveal drift.
Convert and fit
Convert mA to A and fit I = mV + b without forcing the intercept to zero. Inspect residuals and intercept.
Why this step matters
The inverse-gradient formula requires amperes, and an intercept can expose offsets.
Report resistance
Calculate R = 1/m in Ω. State fit-only error separately from meter, loading and temperature uncertainties, and label these observations simulated.
Why this step matters
A numerical resistance needs units and a defensible account of its limitations.
YOUR NOTEBOOK · 0 OBSERVATIONS
Turn measurements into a result.
Points are your observations. The fit uses SI x and y values before display scaling.
LINEAR FIT · y = mx + b
I = mV + b; R = 1/m (I in amperes)
| # | Applied voltage V (V) | Current I (mA) | Voltage V (V) | Current I (mA) | Remove |
|---|
No readings yet. Take a virtual measurement and record it.
Calculate it yourself.
CHECK YOUR UNDERSTANDING