Resistors in Parallel: Current Divides

1 · Predict

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?

• Total current goes down — a bigger R2 branch carries less current, and the other branch is unaffected.
• Total current goes up as R2 increases.
• Total current doesn't depend on R2.

2 · Set Up

1. Open the parallel-resistors preset and press Reset. R1 = 100 Ω is fixed; the battery supplies 6 V across both branches.
2. Enable the current readout on both resistors and the battery.
3. Set R2's value for each trial and record the total current drawn from the battery.

3 · Collect Data

Plot total current I_total (y-axis) against 1/R2 (x-axis) for your three trials.

4 · Analyze

1. 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.
2. 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.

5 · Extend

1. 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.
2. 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.

The Physics Behind This Experiment

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