Design a reliable warning circuit.

Introductory guided version: one instruction at a time, automatic zero check, recorded readings, and calculations. The procedure and rubric below apply to the optional advanced investigation.

Students test a resistor dummy load for a fictional warning module. The goal is an evidence-based recommendation that meets current and power requirements, not an actual outdoor-device design.

Learning outcomes and evidence

Outcome	Student evidence
Plan a controlled comparison.	Correct independent/dependent variables; one fixed control; a justified hypothesis; three conditions with three readings each.
Use measuring instruments.	Correct meter placement; zero check; opening the switch before adjusting settings; accurate V and mA transcription.
Analyze quantitative relationships.	Means, nominal Ohm’s-law predictions, load power, percent deviation, and an appropriate graph with units.
Use evidence to solve a constrained problem.	A configuration tested at least three times that stays within 35–55 mA and ≤0.250 W.
Evaluate limitations and transfer learning.	Distinguishes repeat variation from resistor tolerance; identifies untested outdoor/device factors.

Prerequisites: voltage, current, resistance; series and parallel connections; arithmetic means; conversion from mA to A. Supported mode supplies the procedure and calculation scaffold. Independent mode requires students to write their procedure and omits the formula scaffold. Both have the same evidence requirements.

Suggested classroom sequence

Launch (5 minutes): Discuss why a design can meet a current target while exceeding a power rating. Clarify the dummy-load model.
Plan (5–8 minutes): Review the hypothesis and controlled variable. In independent mode, approve the actual student procedure before they proceed; the app only checks that text is present.
Build and collect (12–15 minutes): Students assemble, zero-check, and take at least nine readings. Have partners alternate operator and recorder roles.
Analyze (8–12 minutes): Check unit conversions, the choice of graph axes, mean values, and variation ranges.
Recommend and discuss (5–10 minutes): Compare designs and ask whether the same evidence establishes real-world reliability.

Reference investigation and likely results

At a fixed 3 V setting, a supported investigation can compare 40, 70, and 100 Ω, taking three readings at each. The modeled resistor has a fixed +2% offset from its nominal label. Readings vary slightly and may repeat because of display resolution.

Nominal load	Ideal prediction	Approximate measured current	Approximate power	Decision
40 Ω	75.0 mA	73–74 mA	0.221 W	Current too high.
70 Ω	42.9 mA	About 42 mA	0.126 W	Meets both constraints with useful margin.
100 Ω	30.0 mA	29–30 mA	0.088 W	Current too low.

Other valid designs exist. For example, 4 V / 100 Ω gives about 39 mA and 0.157 W; students must test their actual recommendation. Judge evidence, not agreement with one preferred answer.

For a voltage investigation, hold 100 Ω constant and compare 2, 3, and 4 V. A 4 V / 100 Ω recommendation can then use the repeated 4 V data. If resistance is the independent variable, current falls nonlinearly as resistance rises; at fixed resistance, current rises approximately linearly with voltage.

Calculation conventions

Predicted current uses nominal supply setting and nominal resistance. Measured power uses mean measured voltage × mean measured current converted to A. Percent difference is absolute deviation from the ideal prediction, divided by that prediction. Accepted entry tolerances: ±0.15 mA for the mean, ±0.2 mA for prediction, ±0.003 W for power, and ±0.25 percentage points for percent difference. Students can report more precision, but should discuss the 1 mA display resolution.

Assessment rubric · 20 points

Score each criterion from 0–4. A complete numeric readiness checklist does not assign this grade.

Criterion	4 · Strong	2 · Developing	0 · Missing
Planning	Clear, reasoned hypothesis; suitable variables, controls, settings, repeats, and procedure.	Basic plan, but control or reasoning needs revision.	No usable plan.
Procedure and data	Correct instrument placement/zero check; accurate units and ≥3 settings × ≥3 readings; meaningful observations.	Partial data, weak repeat structure, or inconsistent controls.	No credible measurement evidence.
Analysis	Correct calculations and axes; interprets trend and observed ranges using scientific concepts.	Some correct calculations, with weak interpretation or unit errors.	No supported quantitative analysis.
Recommendation	Meets both constraints, cites repeat evidence and power, and explains choice with Ohm’s law and design margin.	Reasonable claim, but evidence or constraint evaluation is incomplete.	Unsupported recommendation.
Limitations and application	Distinguishes variability, resolution, tolerance, and model limits; proposes a concrete next test for a real device.	Names generic errors or real-world factors without explaining effects.	No consideration of limitations.

Use 1 or 3 for work between the anchors. Read and evaluate the written explanation; the app checks presence, not scientific quality.

Discussion prompts

Why does a small difference between predicted and measured current not automatically mean a mistake?
Why can repeating a measurement produce the same displayed value?
Can increasing voltage improve performance and still create a power problem?
Does testing only one operating setting show a relationship?
What evidence would establish battery life, weather resistance, or actual module performance?

Simulation limits

The fixed +2% resistance offset represents one possible component tolerance, not a universal property of resistors. Supply variation, display noise, and resolution are explicitly modeled. Zero check removes a preset +2 mA offset. Wires and meters otherwise have ideal resistance; resistor heating, supply droop, battery depletion, and real module behavior are excluded. The overload stop is a teaching interlock. It is not a substitute for laboratory electrical safety guidance.

Every run samples one paired voltage/current observation. Repeated clicks on a meter do not generate independent data; students must record, then energize a new trial. All raw trials remain in the notebook. Controlled-comparison graphs include only conditions with the planned fixed control; candidate design trials may use other settings.

Background science

Ammeters measure in series and voltmeters across a component; electrical power is calculated from voltage and current.

OpenStax: Electrical measuring instruments
OpenStax: Electrical energy and power

This procedure, fictional design brief, and rubric are original instructional content. Background links provide references for the underlying science.

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