A little electricity.
What makes a light turn on?
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What makes a light turn on?
Fit a fuse.
Closing the switch completes the circuit. In series, both bulbs share one path and the same current. In parallel, each bulb has its own path across the full battery voltage. Resistance limits current, and electrical power sets brightness.
Ideal DC source, wires and fixed-resistance bulbs. A 4 A fast-acting fuse (Littelfuse 217, 0.0165 Ω) sits between the battery and its + terminal. Its datasheet says it carries 1.5 times its rating for at least an hour and opens within 30 minutes at 2.1 times, and within 0.02 s at 10 times. A direct wire between the battery terminals is a short circuit that only the fuse limits, so the fuse blows. The short reading is prospective current before opening, not a real battery output prediction. Source impedance, arcing and thermal timing are omitted. Conventional current is shown; visual particle speed is schematic.
Give both 12 Ω bulbs more than 6 W from a 9 V battery.
Compare bulb power in series and parallel.