Use two measurements to isolate a fault
Does a low loaded voltage identify a unique problem?
Entering midway? Revisit Insulation and thermal mass solve different problems for the preceding worked example, or start here and use the explanation below.
Start with a concrete question
Original synthetic scenario. A virtual circuit may be healthy, have lower source voltage, or have excessive internal resistance. A shared meter offset can affect both voltage readings.
Try the initial inputs, then write a prediction before changing one setting. All calculations run locally on your CPU.
What do you expect?
Can open-circuit and loaded readings distinguish low source voltage from high internal resistance?
Change one thing. Inspect what happens.
- Compare the three faults at the same 4-ohm load.
- Use the open reading to distinguish source level; use loaded sag to inspect resistance.
- Change load and check whether the favored hypothesis still fits both readings.
- Add meter offset and propose a calibration check before declaring a fault.
Your settingsMechanism
Calculation belowEvidence
Compare outcomes
Compare the current results
Every bar starts at zero and uses the same numeric scale in this chart. The upper bound automatically adjusts to the largest current value (at least 1), so compare the numbers when changing inputs. Units and quantities come from each label; different kinds of quantity are not interchangeable. Displayed values are rounded to at most six significant digits.Follow the calculation
- Selected fault defines source 9 V and internal resistance 1 ohms.
- Open circuit has zero current, so terminal voltage = 9; meter offset gives 9 V.
- With 4 ohm load: I = 9 / (4 + 1) = 1.800 A.
- Loaded voltage = 4 × 1.800 = 7.200 V; meter reads 7.200 V.
- Each candidate is scored against BOTH readings; do not diagnose from a voltage drop alone.
Different faults can lower loaded voltage. An open-circuit measurement and a loaded measurement provide complementary evidence, while meter bias can mislead both.
Captures keep your inputs, prediction and observation. Results are recalculated from those inputs. Resetting inputs keeps your captures and challenge history.
Explain the mechanism
What the experiment explains
Original synthetic scenario. A virtual circuit may be healthy, have lower source voltage, or have excessive internal resistance. A shared meter offset can affect both voltage readings.
A source with internal resistance loses terminal voltage when current flows. A lower source voltage also lowers the loaded reading, so one symptom can have multiple causes.
For the default low-source case, open voltage is 9 V. With a 4-ohm load and 1-ohm internal resistance, current is 9/5 = 1.8 A and loaded voltage is 7.2 V.
The candidate scores sum absolute residuals from both readings. A small residual supports a model comparison; it does not rule out unmodeled faults or a biased instrument.
Read the relationship
Open voltage = source voltage. Loaded voltage = source voltage × load/(load + internal resistance). Candidate error = sum of absolute observed-minus-predicted voltage differences.
Inspect the evidence
The numerical trace is recalculated from your current settings. Compare a controlled pair of trials before changing several inputs together. Inspect intermediate quantities as well as final metrics; state which assumptions make the comparison meaningful.
Boundaries of the model
- Three fixed hypotheses and ideal resistors; no intermittent faults or temperature effects.
- Fault selector reveals instructional ground truth; real diagnosis would use independent measurements.
Return to the physics and engineering course and project to connect this mechanism to the broader investigation.
Try a fresh case
A new circuit has open voltage 10 V and loaded voltage 8 V across a 4-ohm resistor. Under this ideal model, what is its internal resistance?
This is a public practice check. Retries support learning; matching a number does not certify independent proficiency.
Take the investigation further
Choose any extension. These are project prompts for you to carry out; they are not automatically assessed.
School investigation
Draw a decision tree using two measurements and include an inconclusive branch.
College investigation
Fit source voltage and resistance from multiple noisy load measurements and assess identifiability.
Workplace investigation
Write a troubleshooting checklist with instrument checks, competing causes and evidence required before replacement.
Keep the evidence, choose your next step
Completion records your own decision that you have worked through this investigation. Practice checks and independent project evidence are separate.