Circuits
Parallel resistors
Shared voltage, split current (current divider)
Wire resistors in parallel and compare branch currents and equivalent resistance. Interactive circuit lab for series-parallel analysis and Kirchhoff's rules.
Parallel resistors
Resistors in parallel share the same voltage but split the current — a current divider.
Each branch connects to the same two nodes, so the voltage across each resistor is identical. Current divides inversely with resistance.
- V is the same across each branch
- I_total = I₁ + I₂
Investigation brief
Plan the question before you open the lab
The brief mirrors the prerendered page: driving question, competing predictions, variable roles, governing laws, setup, analysis and extension prompts remain visible and in this order.
Driving question
Two resistors are connected in parallel (side by side) across a 6 V battery, so both see the full battery voltage. If you increase the second resistor's value, does the total current drawn from the battery go up or down?
Predictions to weigh
- Total current goes up as R2 increases.
- Total current doesn't depend on R2.
- Total current goes down — a bigger R2 branch carries less current, and the other branch is unaffected.
Variable roles
What you set:
- Resistor R2 (Ω)
What you measure:
- Equivalent resistance R_p (Ω)
- Total current I_total (A)
How the investigation runs
- Open the parallel-resistors preset and press Reset. R1 = 100 Ω is fixed; the battery supplies 6 V across both branches.
- Enable the current readout on both resistors and the battery.
- Set R2's value for each trial and record the total current drawn from the battery.
Governing equation
Parallel Resistance — V = I·R
Resistors in parallel combine by reciprocals: 1/R_p = 1/R1 + 1/R2. Each branch sees the full source voltage and draws its own current independently, I = V/R for that branch alone.
What the printable worksheet asks students to work out
- For one trial, compute R_p = 1/(1/R1 + 1/R2), then I_total = E/R_p using E = 6 V, R1 = 100 Ω. Compare to the table. Also verify I_total = E/R1 + E/R2 gives the same answer.
- R1's branch current stays fixed at E/R1 = 0.06 A regardless of R2. Explain why each parallel branch's current only depends on its own resistance, not on the other branch's.
Where this shows up beyond the lab
- Household outlets are wired in parallel, not series, so each appliance sees the full 120 V (or 230 V) independently. Explain why series wiring would be impractical for a house full of independently-switched appliances.
- The equivalent resistance of a parallel combination is always smaller than either individual resistor. Explain why adding a second current path can only make it easier (never harder) for charge to flow.
- AP Physics 2 — Unit 11: Electric Circuits
- AP Physics C: Electricity and Magnetism — Unit 11: Electric Circuits
- IB Physics — B.5 Current and circuits
- General High School Physics — Electricity & DC circuits
- NGSS High School Physics — Electric current and magnetic fields
- Welcome to Parallel Resistors
- Select the first resistor
- Press Play
- Split current
- Open the Properties panel
- You did it!
Open the interactive simulation to build the scene, press Play, and explore with live measurements and a guided tutorial.