Turtleand Energy

Rung 1 · See the loop

Close the loop

Build one source, one switch, and one load so open and closed paths become visible.

starter15 minutes0 of 4 stages explored
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A five volt source, switch, and one hundred ohm resistor connected in one series loop.
5 V source -> switch -> 100 ohm resistor -> return

Knowledge this exercise builds on

Lesson 1: Electricity from first principlesLesson 3: Simple circuits from first principles

Practice loop

Try each step before revealing its answer.

The task stays visible. Revealing a numbered answer remembers that stage as explored in this browser. It is not a grade.

ComponentsSee the parts and values before you start.
  • One 5 V DC voltage source
  • One switch
  • One 100 Ω resistor
  • Wires and one ground reference
PredictCommit to an expected result before running the circuit.

Before running the circuit, predict the current with the switch open and with it closed. Decide whether the source still maintains voltage while the path is open.

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With the switch open, the current is 0 A. The source still maintains 5 V across its terminals, but the broken path prevents sustained current. With the switch closed:

I = V / R = 5 V / 100 Ω = 0.05 A

The closed-loop current is 50 mA.

BuildWire the circuit yourself from a blank canvas.

Start from a blank Falstad circuit. Draw one complete series loop, then place the switch between the source and resistor. Keep the switch open for the first observation.

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The only path should be:

5 V source -> switch -> 100 Ω resistor -> source return

Place the ground reference at the source return. The open switch should be the only intentional break in the loop.

MeasureSee what to inspect, compare, and change.

Open the resistor in a scope and record its current and voltage with the switch open and closed. Compare the two readings before revealing the expected result.

Reveal expected resultHide expected result

The resistor current is 0 A while the switch is open and about 50 mA after it closes. The closed resistor drop is about 5 V.

ExplainConnect the observation back to your model.

Explain why the source can still maintain a voltage while the open switch prevents sustained current. Name the source, controlled path, load, and return path.

Reveal explanationHide explanation

Voltage can exist across an open path, but sustained current needs a complete loop. The voltage source provides the electrical push, the switch controls the path, the resistor is the load, and the wire back to the source is the return. Closing the switch completes the loop and allows the source to transfer energy through the resistor.

Optional referenceReveal reference circuitCompare only after you build. Opening this panel does not contact Falstad.

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Safety boundary

This is a low-voltage educational model.

Do not translate it into mains construction, household wiring, battery-pack work, or real protection settings. Real electrical systems need rated components, proper protection, test equipment, and qualified safety judgment.