Before you touch the controls
Draw a series circuit and a parallel circuit. Predict how adding a second resistor changes the current supplied by the same ideal battery in each case.
Change one thing at a time
- Choose a supply voltage and a resistor value. Keep the voltage fixed, close the switch and record the single-resistor current.
- Add a resistor in series. Record total resistance and current. Calculate a prediction using I = V/R.
- Change to parallel. Record total current and the branch currents. Compare their sum with the supply current.
- Turn on the current-flow overlay. Trace the complete paths, then explain how the visual arrows relate to the meter readings.
Record your observations
| Circuit arrangement | Supply voltage | Equivalent resistance | Supply current |
|---|---|---|---|
| Trial 1 | — | — | — |
| Trial 2 | — | — | — |
| Trial 3 | — | — | — |
| Trial 4 | — | — | — |
Use this table as a worksheet, or record the available measurements in the lab notebook. Export your observations before refreshing or closing the lab.
Turn measurements into an explanation
- Why does an extra parallel branch increase the supply current?
- How do the potential differences across components compare in series and parallel?
- Where is energy transferred, and why is current not “used up” by a resistor?
Think about the model
The basic circuit model uses ideal connections and the component assumptions stated in the lab. A real battery may have internal resistance and a filament lamp is not a constant-resistance component.
Take it further
Use unequal parallel resistors. Predict which branch takes more current, then compare your calculation with the meters.