Thermistor voltage divider

Predict how a falling thermistor resistance changes a divider voltage.

Physics Phoebe, your practice guide

Physics Phoebe
Predict the reading, then compare it with the measurement.

Falstad CircuitJS

Third party Tool

Tier 1 · Web · No account

Version tested: Browser tool opened 2026-09-05; no version number exposed. Date: 2026-09-05.

Open the prepared circuit.

Open this circuit in Falstad (new tab)

Steps

Screens captured against Falstad CircuitJS Browser tool opened 2026-09-05; no version number exposed on 2026-09-05; the tool may have moved on — the text steps are the contract.

  1. Step 1

    Do
    In the circuit canvas, inspect the 5 V source and the two 10 kΩ resistors.
    You will see
    Source panel: "I = 250 μA"; "Vd = 5 V". Upper resistor panel: "R = 10 kΩ"; "Vd = 2.5 V". Lower resistor panel: "R = 10 kΩ"; "Vd = 2.5 V". Midpoint wire panel: "V = 2.5 V".
    Why it matters
    Expected: Two 10 kΩ resistors divide 5 V equally, giving 2.5 V at the midpoint. Meaning: The lower resistor models the thermistor; temperature itself is not simulated here.

  2. Step 2

    Do
    In the circuit canvas, point at the wire leaving the midpoint and read its measurement panel.
    You will see
    Source panel: "I = 250 μA"; "Vd = 5 V". Upper resistor panel: "R = 10 kΩ"; "Vd = 2.5 V". Lower resistor panel: "R = 10 kΩ"; "Vd = 2.5 V". Midpoint wire panel: "V = 2.5 V".
    Why it matters
    Expected: 5 × 10/(10+10) = 2.5 V. Meaning: A grounded lower resistor makes its voltage drop equal the midpoint voltage.

  3. Step 3

    Do
    In the circuit canvas, use the resistor labels to calculate 5 × 10000 / (10000 + 10000).
    You will see
    Source panel: "I = 250 μA"; "Vd = 5 V". Upper resistor panel: "R = 10 kΩ"; "Vd = 2.5 V". Lower resistor panel: "R = 10 kΩ"; "Vd = 2.5 V". Midpoint wire panel: "V = 2.5 V".
    Why it matters
    Expected: 10 kΩ + 10 kΩ = 20 kΩ and each resistor takes half the supply. Meaning: The observed midpoint checks the divider rule before changing the model.

  4. Step 4

    Do
    In the lower resistor’s right-click menu, choose Edit and set Resistance to 5000 Ω.
    You will see
    Source panel: "I = 333.333 μA"; "Vd = 5 V". Upper resistor panel: "R = 10 kΩ"; "Vd = 3.333 V". Lower resistor panel: "R = 5 kΩ"; "Vd = 1.667 V". Midpoint wire panel: "V = 1.667 V".
    Why it matters
    Expected: With a 5 kΩ lower resistor, 5 × 5/(10+5) = 1.667 V. Meaning: A smaller lower resistance gives it a smaller share of the supply.

  5. Step 5

    Do
    In the lower resistor’s right-click menu, choose Edit and set Resistance to 20000 Ω.
    You will see
    Source panel: "I = 166.667 μA"; "Vd = 5 V". Upper resistor panel: "R = 10 kΩ"; "Vd = 1.667 V". Lower resistor panel: "R = 20 kΩ"; "Vd = 3.333 V". Midpoint wire panel: "V = 3.333 V".
    Why it matters
    Expected: With a 20 kΩ lower resistor, 5 × 20/(10+20) = 3.333 V. Meaning: A larger lower resistance raises the midpoint voltage.

  6. Step 6

    Do
    In the lower resistor’s right-click menu, choose Edit and restore Resistance to 10000 Ω.
    You will see
    Source panel: "I = 250 μA"; "Vd = 5 V". Upper resistor panel: "R = 10 kΩ"; "Vd = 2.5 V". Lower resistor panel: "R = 10 kΩ"; "Vd = 2.5 V". Midpoint wire panel: "V = 2.5 V".
    Why it matters
    Expected: Restoring 10 kΩ should restore the 2.5 V midpoint. Meaning: The reversible edit separates resistance response from any assumed temperature law.

Chapter checks

These questions refer to the chapter’s examples. Use the return links to review their answers.

  1. Why does a resistive sensor such as a thermistor or LDR usually need a voltage-divider circuit before it can be read by a microcontroller?

    Return to the chapter’s knowledge check

  2. A divider uses a fixed top resistor and a sensor bottom resistor, fed from the same 3.3 V rail that supplies the ADC reference. The 3.3 V rail sags to 3.1 V under load. What happens to the ADC code for a fixed sensor resistance?

    Return to the chapter’s knowledge check

Return to Resistive Dividers and ADC Loading · Browse Labs