IBEW / DC circuit challenges

Chapter 4 · Build · Measure · Calculate · Explain

Can you prove your circuit works?

Five practical challenges with help when you need it. Try the task independently, then reveal a walkthrough, schematic or breadboard layout. Compare your predictions with real readings and explain the difference.

Public practice, not a submitted or automatically graded exam. No sign-in or saving. Entries remain only in this open page and are lost on reload or leaving the page. Record your work on paper if you need to keep it.

Challenge 1 of 5

Resistance · Ohm’s law · Series current

Predict and prove the current

Build one series path through three 220 Ω resistors. Predict the current, then test whether it is the same at two positions.

Parts: 3 V two-AAA pack, three 220 Ω resistors, breadboard, jumpers and a suitable fused multimeter.

Your evidence before moving onRecord total resistance, predicted current, both measured currents in mA, and why the two positions should carry the same current.

Try first. Open only the help you need. Record on paper or use the optional fields below.

1 Build the circuit

Identify the resistors from their markings, measure each in isolation, and build the three-resistor series circuit. Leave the pack disconnected for the wiring check.

Stop before power: show the unpowered wiring and planned meter connections to the instructor. A diagram or checked calculation is not a physical safety approval.

Walk me through the build
  1. For four-band 220 Ω ±5% parts, red–red–brown–gold means 22 × 10 Ω, ±5%. A five-band part uses a different digit count. Check your actual markings.
  2. With both pack leads disconnected, measure each isolated resistor in Ω and record it below. For a marked 220 Ω ±5% part, the nominal tolerance interval is 209–231 Ω; meter uncertainty is separate.
  3. Connect positive → R1 → R2 → R3 → negative. Each resistor must bridge different connected strips. The schematic shows relationships; the breadboard help shows one layout.
  4. Show the unpowered build to the instructor. Do not connect power until the wiring is checked.
Reveal the wiring schematic
Three resistors in seriesPositive to R1 to R2 to R3 to negative. Each resistor is 220 ohms. Voltage is measured across named nodes without removing a jumper.+−3 V · 2×AAAR1 · 220 ΩR2 · 220 ΩR3 · 220 ΩABCDFor current tests, use the meter-insertion diagrams below.

Trace one path from source positive back to negative. Dots mark junctions; the physical layout can look different. On a small screen, scroll the diagram sideways to read it.

Reveal a breadboard layout
Breadboard for three series resistorsA through E in each numbered column are connected; F through J form a separate connected group. Power rails are unused. R1 E3 to E8; R2 E12 to E17; R3 E21 to E26. Positive connects A3; negative returns from A26. Green jumpers join the resistor sections. Curves crossing other wires or holes do not make junctions; only endpoints connect.Connected strips, not wire shapes, determine the circuit.Center channel — no internal connection across it123456789101112131415161718192021222324252627282930ABCDEFGHIJ3 V pack2×AAA+ −R1 · 220 ΩR2 · 220 ΩR3 · 220 ΩABCDA–E share each column. F–J share each column separately. No power rails are used.

This is one valid layout. Only the wire endpoints plug into holes; a drawn wire passing over another hole or insulated wire does not connect there. Verify your actual board’s internal strips with power disconnected. On a small screen, scroll the diagram sideways.

  • R1: E3–E8. R2: E12–E17. R3: E21–E26.
  • Positive: A3. Negative return: A26.
  • Join A8–A12. Join A17–A21.
  • Node A: column 3. Node B: columns 8 and 12 joined by their jumper. Node C: columns 17 and 21 joined by their jumper. Node D: column 26.
Show exactly where the current meter replaces a jumper

Power off for every change. Use the actual meter’s suitable fused DC-current input and range. These are alternatives: restore the previous jumper before moving to the next position.

Position 1 — replace the return jumper after R3

Three resistors in series with an ammeter replacing the return jumperPositive to R1 to R2 to R3 to negative. Each resistor is 220 ohms. The meter replaces, not parallels, one jumper. Disconnect the pack before changing the connection.+−3 V · 2×AAAR1 · 220 ΩR2 · 220 ΩR3 · 220 ΩACOM ← meter ← red from R3ABCD
Breadboard for three series resistors with the meter replacing the return jumperA through E in each numbered column are connected; F through J form a separate connected group. Power rails are unused. R1 E3 to E8; R2 E12 to E17; R3 E21 to E26. Positive connects A3; negative returns from A26. Green jumpers join the resistor sections. The black return jumper is removed and replaced by a series ammeter: red toward R3, COM toward negative. Curves crossing other wires or holes do not make junctions; only endpoints connect.Connected strips, not wire shapes, determine the circuit.Center channel — no internal connection across it123456789101112131415161718192021222324252627282930ABCDEFGHIJ3 V pack2×AAA+ −ACOM toward −Red toward R3R1 · 220 ΩR2 · 220 ΩR3 · 220 ΩA–E share each column. F–J share each column separately. No power rails are used.

Position 2 — replace the R1-to-R2 link

Three resistors in series with an ammeter replacing the R1-to-R2 linkPositive to R1 to R2 to R3 to negative. Each resistor is 220 ohms. The meter replaces, not parallels, one jumper. Disconnect the pack before changing the connection.+−3 V · 2×AAAR1 · 220 ΩR2 · 220 ΩR3 · 220 ΩARed toward R1 · COM toward R2ACD
Breadboard for three series resistors with the meter replacing the R1-to-R2 linkA through E in each numbered column are connected; F through J form a separate connected group. Power rails are unused. R1 E3 to E8; R2 E12 to E17; R3 E21 to E26. Positive connects A3; negative returns from A26. Green jumpers join the resistor sections. The A8 to A12 jumper is removed and replaced by a series ammeter: red toward R1, COM toward R2. Curves crossing other wires or holes do not make junctions; only endpoints connect.Connected strips, not wire shapes, determine the circuit.Center channel — no internal connection across it123456789101112131415161718192021222324252627282930ABCDEFGHIJ3 V pack2×AAA+ −R1 · 220 ΩR2 · 220 ΩR3 · 220 ΩARed → R1COM → R2A–E share each column. F–J share each column separately. No power rails are used.

Never add an ammeter across the source or leave the original jumper around it. Disconnect afterward, restore the circuit, and return the red lead to V/Ω.

2 Measure and record

Measure the isolated resistors first, then source voltage and the two series-current positions using the checked procedure.

Where do my probes go and what meter setting do I use?
  1. After the wiring check, use DC volts with leads in COM and V/Ω to measure across the pack while the resistor circuit is connected. Disconnect the pack again.
  2. For current position 1, remove the return jumper after R3. Have the instructor check the meter’s actual fused current input, DC-current range and series connection. The red current lead goes toward R3; COM goes toward pack negative. Reconnect only to read current, then disconnect.
  3. Remove the meter and restore the return jumper. For position 2, remove the R1-to-R2 link instead. Red goes toward R1; COM toward R2. Have this new connection checked before powering it.
  4. Disconnect, remove the meter, restore the link, and return the red lead to V/Ω. Never leave a jumper in parallel with the ammeter. Use the current-placement diagrams below if needed.

Enter the units shown: Ω, V, mA or W. Use your own readings, not the ideal example. A near-zero voltage/current reading can be valid; an isolated resistance or verified rating must be positive.

3 Calculate and check

Work the calculation yourself first. The checker uses your measurement inputs; it checks arithmetic, not your wiring, meter technique or physical diagnosis.

Walk me through the calculation and units
  1. Add your measured R1, R2 and R3: Rt = R1 + R2 + R3, in ohms.
  2. Divide the measured loaded source voltage by Rt: I = E ÷ Rt, in amperes.
  3. Multiply amperes by 1000 to report milliamperes. Compare that prediction with the two current readings. Do not add the two readings together.
  4. Small differences can reflect battery changes, contact resistance, meter burden and measurement uncertainty. A large difference calls for an unpowered wiring and meter check, not invented readings.
Reveal a complete worked example with sample numbers
  1. Ideal example only: R1 = R2 = R3 = 220 Ω; E = 3.00 V.
  2. Rt = 220 + 220 + 220 = 660 Ω.
  3. I = 3.00 ÷ 660 = 0.004545 A = 4.545 mA at either position.

4 Explain what the results mean

Help me understand the explanation

There is only one steady current path. Resistors transfer energy; they do not use up charge. The same current passes each position. Equal current does not mean equal voltage across sections with different resistance: V = I × R. Challenge 2 builds a separate adjustable voltage divider to investigate that relationship. For a large current-reading difference, check the source, circuit, meter input/range and connections.

Finish safely: disconnect the pack, restore the known-good components and connections, and return the red meter lead to V/Ω after a current test. For the mystery challenge, get the repaired wiring checked before repeating the light/shade test.

Review the matching student lab slides →
Next: 2 · Voltage divider — a new build. Record your current results, disconnect the pack and take apart the three-resistor circuit. Return the red meter lead to V/Ω. Build the separate three-terminal pot divider using its own diagrams, then predict and measure two output voltages.