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Voltage and Current Water Analogy

Run the Voltage and Current Water Analogy MicroSim Fullscreen

About This MicroSim

Electricity is hard to see, but water is easy to picture. This MicroSim puts two loops side by side. On the left, a pump pushes water around a pipe. On the right, a battery pack pushes electric charge around a wire.

  • Voltage is like water pressure. It is the push. More batteries in series give more push.
  • Current is like water flow. It is how much moves past a point each second. We measure current in amps (A).
  • Resistance is like a narrow pipe. Your robot's motor is the narrow part of the loop. A narrower pipe lets less water through.

Both loops follow the same rule: current = voltage ÷ resistance. With 4 batteries (6.0 V) and a 12-ohm motor, the current is 6.0 ÷ 12 = 0.50 A.

How to Use

  1. Move your mouse over the MicroSim to start the dots moving. Blue dots are water. Yellow dots are charge. They always move at the same speed.
  2. Predict, then test. Before you move the Voltage slider, guess what will happen to the flow. Then drag it and check the Current bar.
  3. Change the Motor resistance. Watch the narrow pipe get thinner and the dots slow down.
  4. Press Break the loop. The valve closes and the switch opens. What happens to the dots? Press Fix the loop to close it again.

Challenge: Set the sliders so the current is exactly 0.30 A. Then explain in one sentence why the dots stop when you break the loop. The ideas behind this MicroSim are in Chapter 1: Voltage and Current.

Iframe Embed Code

You can add this MicroSim to any web page by adding this to your HTML:

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<iframe src="https://dmccreary.github.io/stem-robots/sims/voltage-current-water-analogy/main.html"
        height="447px"
        width="100%"
        scrolling="no"></iframe>

Lesson Plan

Learning Objective

Students will explain voltage as the push (pressure) that drives charge and current as the rate of flow, and will predict how current changes when voltage, resistance, or loop continuity changes (Bloom's Taxonomy: Understand).

Grade Level

Grades 8–12. No prior physics course is assumed; the division is the only mathematics required.

Duration

15 minutes.

Prerequisites

  • The "Voltage and Current" section of Chapter 1, including the water-tower picture of voltage and the unit names volt and amp.
  • The fact that four 1.5 V AA batteries in series give 6 V.

Design Notes

The two panels share one model, so every change appears in both representations at once. Dual representations of this kind help novices map a concrete source domain (water) onto an abstract target domain (charge), provided the correspondences are made explicit (Gentner & Gentner, 1983). The MicroSim therefore labels each mapping ("Pump = Battery", "Narrow pipe = Motor") and shows matching numeric meters. The dots move only while the pointer is over the MicroSim; the meters and the formula line carry the same information when the animation is paused.

The analogy has known limits worth naming in class: water leaks out of a broken pipe, but charge does not spill out of a broken wire; and the motor's resistance is not truly constant as it spins.

Activities

  1. Predict (3 min). With the MicroSim at its defaults (6.0 V, 12 ohms, 0.50 A), ask: "What happens to the current if we use only 2 batteries?" Students write a prediction and a reason (answer: it halves to 0.25 A).
  2. Observe (4 min). Students test the prediction, then test the effect of raising the resistance from 12 to 24 ohms at 6.0 V (answer: 0.25 A).
  3. Explain (3 min). Students complete the sentence: "More voltage makes the current ___ because ; more resistance makes the current ___ because ."
  4. Challenge (3 min). Students find a setting that gives exactly 0.30 A. Four settings work: 1 battery with 5 ohms, 2 batteries with 10 ohms, 3 batteries with 15 ohms, and 4 batteries with 20 ohms.
  5. Connect (2 min). Students break the loop and explain why a loose wire stops the whole robot, linking to the chapter's "Basic Circuits" section.

Assessment

  • Formative: Compare each student's written prediction from Activity 1 with the observed result, and ask students who predicted incorrectly to revise their reasoning.
  • Exit ticket: "Your robot's motors run slowly. Using the water analogy, give two different reasons this could happen." (Expected: weak batteries mean lower pressure; a stiff or jammed motor means a narrower pipe.)
  • Rubric (4-point): Exemplary — correctly maps pressure to voltage and flow to current, predicts direction and size of change, and names a limit of the analogy; Proficient — correct mapping and direction of change; Developing — correct mapping but confuses which quantity changes; Beginning — treats voltage and current as the same thing.

References

  1. Chapter 1: Introduction to Computational Thinking and Physical Computing — voltage, current, basic circuits, and the battery pack.
  2. Hydraulic analogy — Wikipedia — the water-pipe model of electric circuits and its limits.
  3. Ohm's law — Wikipedia — the relationship current = voltage ÷ resistance.
  4. Electric current — Wikipedia — what current is and how it is measured in amperes.
  5. Gentner, D., & Gentner, D. R. (1983). Flowing waters or teeming crowds: Mental models of electricity. In D. Gentner & A. L. Stevens (Eds.), Mental Models (pp. 99–129). Lawrence Erlbaum.
  6. Ohm's Law Calculator MicroSim (Learning MicroPython) — the current-flow loop this MicroSim reuses.