This investigation compares the brightness of bulbs when connected in series versus parallel. Students measure current and potential difference in each case to relate electrical quantities to observed brightness.

1. Build a simple series circuit with one bulb and a battery. Insert an ammeter in series with the loop and a voltmeter across the bulb.
2. Switch on the circuit, observe the brightness of the bulb, and record current (A) and potential difference (V).
3. Add a second bulb in series. Note brightness of both bulbs and record new current and voltage values for each bulb.
4. Extend to circuits with three or four bulbs in series, recording brightness, current, and potential difference.
5. Construct parallel circuits: connect two bulbs, each on its own branch, across the battery. Place an ammeter in each branch and a voltmeter across each bulb.
6. Repeat with three and then four bulbs, each on separate parallel branches. Record brightness, current in each branch, and voltage across each bulb.
7. Compare results in a table showing brightness, current, and potential difference for each bulb across all circuit types.

Electric Circuits: Series and Parallel - funsciencedemos :

Series & Parallel Circuits - Patrick Haney:

📄 Investigating bulb brightness experiment - BBC Bitesize: https://www.bbc.co.uk/bitesize/guides/zsk4msg/revision/4

• Use bulbs of different wattage ratings to compare brightness in mixed series and parallel circuits.
• Replace one branch of the parallel circuit with two bulbs in series, and compare with a single bulb on another branch.
• Try repeating with LEDs (with suitable resistors) instead of filament bulbs.

• Use a low-voltage supply (e.g., cells or a lab power supply set to a safe voltage).
• Switch off between readings to prevent bulbs from overheating.
• Place equipment on a heatproof mat to avoid scorching surfaces.
• Do not exceed the recommended supply voltage for the bulbs to avoid breakage.
• Handle bulbs carefully to prevent injury from broken glass if a bulb fails.

• Why do bulbs get dimmer when more are added in series? (Because the supply voltage is shared between bulbs, so each receives less potential difference.)
• Why do bulbs in parallel remain as bright as a single bulb? (Each branch receives the full supply voltage, so each bulb operates at its normal brightness.)
• How does current behave in a series circuit? (The same current flows through every component in series.)
• How does current behave in a parallel circuit? (Branch currents add together to equal the total current from the supply.)
• If three identical bulbs are connected in parallel, what happens to the total current compared with one bulb? (It roughly triples, because each branch draws the same current as a single bulb.)