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Electrical & Computer

Circuit Lab

Ohm's law and Kirchhoff's laws, made tangible. Adjust the source voltage and the resistors and the circuit re-solves instantly: node-A voltage, the current through each branch and the total power. It's not a lookup — the network is solved by genuine nodal analysis (a conductance matrix run through Gaussian elimination), the same method used in SPICE, so the numbers are exactly right.

12 VR1 100ΩR2 200Ω300Ω6.55 V

6.55 V

Node A

54.5 mA

Source current

32.7 mA

Through R2

0.65 W

Power

I(R1) 54.5 mA · I(load) 21.8 mA — current splits between R2 and the load at node A.

The method, with your numbers

Ohm's law + series–parallel

  1. 1

    Combine the parallel branch (R2 ∥ Rₗ)

    R∥ = R2·Rₗ / (R2 + Rₗ)

    R∥ = 200·300 / (200 + 300) = 120 Ω

    Both resistors hang between node A and ground, so they act as one — always smaller than either branch alone.

  2. 2

    Total resistance the battery sees

    R_tot = R1 + R∥

    R_tot = 100 + 120 = 220 Ω

  3. 3

    Source current (Ohm's law)

    I = V / R_tot

    I = 12 / 220 = 54.5 mA

    All of this current flows through R1 — the series resistor has no alternative path.

  4. 4

    Node A by the voltage divider

    V_A = V · R∥ / (R1 + R∥)

    V_A = 12 · 120 / 220 = 6.55 V

    This is the LOADED divider — attach a smaller load and R∥ drops, dragging node A down. That sag is why real dividers can't power heavy loads.

  5. 5

    Split the current at node A

    I₂ = V_A / R2 Iₗ = V_A / Rₗ

    I₂ = 6.55 / 200 = 32.7 mA Iₗ = 6.55 / 300 = 21.8 mA

    The smaller resistance takes the bigger share — current favours the easier path (and the two must sum to the source current).

  6. 6

    Power delivered by the source

    P = V · I

    P = 12 · 0.055 = 0.65 W

    Every watt the battery delivers is dissipated as heat across the three resistors.

Drag any control above — every number here recalculates. Want this method for any problem? Step Sheets →

Source V12 V
R1 (series)100 Ω
R2200 Ω
Load Rₗ300 Ω

Increase R1 or drop the load and watch node A sag — the divider equation and Ohm's law, made visible. Solved by real nodal analysis.

How to use this simulation

Ohm's law and Kirchhoff's laws, made tangible. Adjust the source voltage and the resistors and the circuit re-solves instantly: node-A voltage, the current through each branch and the total power. It's not a lookup — the network is solved by genuine nodal analysis (a conductance matrix run through Gaussian elimination), the same method used in SPICE, so the numbers are exactly right.

Everything runs in your browser — no sign-up, no download. Change a value and the result updates instantly, so you can build a feel for how each input shapes the outcome. It pairs with Crameleon's practice exams and step sheets when you want to go from intuition to working the problems.