The short answer

An unloaded pair of equal 10 kΩ resistors in series across 5 V puts its midpoint at 2.5 V relative to source negative. That answer depends on the source, the return and the absence of a significant load.

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Unloaded ten-kilohm voltage dividerA five-volt source feeds two ten-kilohm resistors in series. The output is measured at their junction relative to source negative, without a load. With an ideal source, the output is 2.5 volts.+−Vin = 5 VUpper 10 kΩLower 10 kΩVout = 2.5 VUnloaded output · relative to source −
Unloaded ten-kilohm voltage divider

Use a divider for a reference, not a power supply

Use an isolated regulated 5 V DC source and two series 10 kΩ resistors. Measure their midpoint with a high-impedance voltmeter; add no load. Label the upper resistor R1 and lower R2; power off while wiring.

This is an ideal DC estimate, not a regulated 2.5 V supply: a load, source variation or resistor tolerance shifts the output.

Give the midpoint its own node

Use separate verified strips for A, B and C. Both ends of a resistor on one strip bypass it. Source negative must connect to C.

NodeTerminals joined by wire or a verified stripExpected voltage vs C
A (+5 V)Source +; R1 upper end5 V
B (Vout)R1 lower end; R2 upper end; voltage probe only2.5 V unloaded
C (0 V)R2 lower end; source −; meter COM reference0 V

Predict current, voltage and heat

At 20 kΩ total, the series current is 0.25 mA. Each equal resistor drops 2.5 V: B is 2.5 V above C. The divider rule uses R2 between output and return.

Each resistor dissipates 0.625 mW; check actual ratings and tolerances.

I = 5 V / (10 kΩ + 10 kΩ) = 0.25 mA; Vout = 5 V × 10 kΩ / 20 kΩ = 2.5 V; P(each) = 0.625 mW

Build from the supply to the return

With power off, connect source + to R1, R1 to R2 at B, and R2 to source −. Check rail breaks and the center trench. Never bypass a resistor or join A–C. Test strips with continuity mode only while unpowered.

Leave B unloaded. Even a voltmeter draws current, though high input impedance makes its effect small.

  1. Power off; check both resistor markings and map A, B and C to distinct strips.
  2. Join source + to R1, the R1/R2 junction to B, and R2 to source −.
  3. Check for a direct A–C connection before powering up; leave B without a load.

Check the predictions with voltage mode

With power on, use COM and the voltage jack in DC voltage mode. Read A–C near 5 V, then B–C and A–B near 2.5 V each. Voltage probes go in parallel; never put a current-mode meter across the supply.

Estimate current from a measured resistor drop / 10 kΩ, or power down and insert a fused ammeter in series. Never bridge A and C using a meter's current jack. Return the lead to the voltage jack after a series current test.

Explain a midpoint that is not 2.5 V

B near 0 V suggests checking R1 or a B–C short; near 5 V suggests checking R2, return or a B–A short. Floating nodes can give misleading readings. Verify A–C, then inspect continuity and values with power removed.

Tolerances, source variation or meter loading may shift the reading. An intentional load between B and C acts in parallel with R2 and lowers the ideal output. Measure both resistor drops to check the unloaded assumptions.

Understand output resistance, then repeat

Set the independent ideal source to zero in the model, replacing it with a short on paper. Looking into B–C gives R1 ∥ R2 = 5 kΩ. Never short a real supply.

A hypothetical 10 kΩ B–C load makes the lower leg 5 kΩ, giving about 1.67 V. Keep the first build unloaded. NPNLab's educational browser Lab explores supported resistors and idealized readings; it does not import this article or certify hardware. Compare with real part specifications.

Rout (ideal source set to zero) = R1 ∥ R2 = 5 kΩ; with 10 kΩ load, Vout ≈ 5 V × 5 kΩ / 15 kΩ = 1.67 V

Build an unloaded voltage divider

Keep this recipe open while building in the Lab. The link opens the workspace; it does not import a prebuilt circuit.

Ideal predictions, not measurements: compare these assumptions with the supported model, then verify any real hardware independently.

  • Unloaded Vout (B relative to C): 2.5 V. Ideal 5 V source and two equal 10 kΩ resistors; no load at B.
  • Current through each resistor: 0.25 mA. Ideal series path: 5 V / 20 kΩ.
  • Power in each resistor: 0.625 mW. Ideal estimate: (2.5 V)² / 10 kΩ.
Parts and connections
PartSetting or value
DC supply (DC1)5 V; set a suitable current limit above 0.25 mA
Upper resistor (R1, pins 1 and 2)10 kΩ, rated at least 0.25 W
Lower resistor (R2, pins 1 and 2)10 kΩ, rated at least 0.25 W
NodeTerminals joined
A (+5 V)DC1 + (5V pin); R1 lead 1
B (Vout)R1 lead 2; R2 lead 1; voltage probe + only (no load)
C (return, 0 V)R2 lead 2; DC1 − (GND pin); voltage probe − reference
  1. Set the source to 5 V and both resistors to 10 kΩ; leave the source off while wiring.
  2. Join terminals at A, B and C respectively. Do not join A directly to C or put both leads of either resistor on one node.
  3. Keep B unloaded. Run the model and inspect B relative to C using a voltage probe, then compare both resistor drops.

Check your build

  • A, B and C must be three distinct nodes; B joins only R1 and R2 (plus a voltage probe).
  • Reference the midpoint voltage to C, not to an unconnected GND label.
  • Use voltage mode in parallel; a current-mode meter must never bridge the supply.

Try one change: Optionally add a separate 10 kΩ load from B to C (in parallel with R2). Ideal prediction: Vout ≈ 1.667 V and upper-resistor current ≈ 0.333 mA. This load is not part of the baseline build.

Sources and further reading

Diagrams are simplified teaching illustrations, not measured results or construction plans. See how these guides are prepared.