Resistors in Series: Resistances Add
1 · Predict
Two resistors are connected in series (one after another) across a 12 V battery. If you increase the second resistor's value, does the same current still flow through both?
- Yes — series components share exactly one current, no matter their individual resistances.
- No — current splits between the two resistors.
- Current through each resistor is set independently by its own resistance.
2 · Set Up
- Open the series-resistors preset and press Reset. R1 = 100 Ω is fixed; the battery supplies 12 V.
- Enable the current readout on both resistors.
- Set R2's value for each trial and record the (single, shared) circuit current.
3 · Collect Data
| Resistor R2 (Ω) | Total resistance R_total (Ω) | Current I (A) |
|---|---|---|
| 100 | ||
| 200 | ||
| 300 |
Plot current I (y-axis) against total resistance R_total (x-axis) for your three trials.
4 · Analyze
- For one trial, compute R_total = R1 + R2, then I = E/R_total using E = 12 V, R1 = 100 Ω. Compare to the table.
- Confirm from the sim that the current reading is identical at R1 and at R2. Explain why series components must share exactly one current (there's nowhere else for charge to go).
5 · Extend
- Since both resistors share the same current, the larger resistor gets the larger share of the 12 V. Explain why V = IR means voltage divides in proportion to resistance in a series circuit.
- Old-style Christmas lights were wired in series: if one bulb burned out, the whole string went dark. Explain why, using what you know about series current.
The Physics Behind This Experiment
Series Resistance
Resistors in series add directly: R_total = R1 + R2 + ... Since only one current path exists, the same current I = E/R_total flows through every component.