PhysicsCurrent electricityClass 10Class 12

Circuit builder: interactive simulation

Current is the same everywhere in a series loop; voltage is the same across every branch of a parallel group. Almost every circuit question reduces to these two facts plus Ohm’s law.

Useful for: JEE Main, NEET, CBSE Boards

Try this

Change the arrangement and the resistances and watch the moving dashes: faster dashes mean more current. The cell’s internal resistance is included, so you can also see why the terminal voltage drops when you draw more current.

  1. 1

    Keep E = 12 V, r = 0.5 Ω and R = 4, 6, 12 Ω. Choose Series.

    What you should see

    R_eq = 22 Ω and I ≈ 0.53 A, the same in every resistor.

  2. 2

    Now switch to Parallel with the same values.

    What you should see

    R_eq = 2 Ω, smaller than the smallest resistor. I = 4.8 A and the terminal voltage falls to 9.6 V.

  3. 3

    Try Mixed: R1 + (R2 ∥ R3).

    What you should see

    6 ∥ 12 = 4 Ω, so R_eq = 8 Ω and I ≈ 1.41 A. The current splits 2 : 1 between R2 and R3.

  4. 4

    Set r to 0 and then to the maximum.

    What you should see

    With r = 0 the terminal voltage always equals E. A large r wastes voltage inside the cell.

Formulas behind it

Ohm’s law

V=IRV = IR

Series

Req=R1+R2+R3R_{eq} = R_1 + R_2 + R_3

Parallel

1Req=1R1+1R2+1R3\frac{1}{R_{eq}} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}

Current from a real cell

I=EReq+rI = \frac{E}{R_{eq} + r}

Terminal voltage

V=E−IrV = E - Ir

Power in a resistor

P=I2R=V2RP = I^2R = \frac{V^2}{R}

Common mistakes

  • Adding parallel resistances directly instead of adding their reciprocals.
  • Forgetting the internal resistance when the question gives one.
  • Thinking current is “used up” along a series circuit. It is the same at every point of a single loop.
  • Using P = I²R with the total current for a resistor in a parallel branch.
Practise 380 questionsCheck your answer instantly, with a worked solution.Current Electricity chapter guideFormula sheet, solved examples and PYQ patterns.Stuck on a circuit builder question?Snap it and get a whiteboard video solution.

FAQ

Why is the parallel combination smaller than every resistor in it?

Each new branch gives the current an extra path, so the total current for the same voltage rises, which means the equivalent resistance falls.

When is the power delivered to the external circuit maximum?

When the external resistance equals the internal resistance (R = r). Then P_max = E²/4r.

Why are household appliances connected in parallel?

Each appliance then gets the full mains voltage and can be switched on or off without affecting the others.

Related simulations

All 65 simulations
Lens ray diagramPhysics, Class 10 & Class 12Electric field linesPhysics, Class 12Refraction and total internal reflectionPhysics, Class 10 & Class 12Human eye & defects of visionPhysics, Class 10 & Class 12Electric motor & Fleming’s left-hand rulePhysics, Class 10 & Class 12Prism refraction, dispersion & rainbowPhysics, Class 10 & Class 12

Want a specific topic or simulation added?

Tell us in our feedback box which chapter or concept you want visualised next.

Send feedback