Two lamps in series and in parallel

Curricula: NGSS 4, KS2, cycle 3, Sek I

Open the full lab ↗

Aim

Compare series and parallel connection of lamps.

The bench

Two circuits with 6 V sources and identical 6 V / 3 W lamps: on the left the lamps are connected in series, on the right in parallel.

Procedure

1. Compare the brightness of the lamps in the two circuits.
2. In the left circuit, select one lamp and delete it with the delete button. Look at the second lamp.
3. Do the same in the right circuit.
4. To restore the bench, use Start over in the lab menu, or open the link again.

Expected result

In series the lamps glow dimly: each gets about 3 V. In parallel both glow almost at full strength: each has about 5.4 V, not 6, because two lamps draw almost 1 A and part of the voltage is lost inside the source. Without one lamp the series circuit is broken and the other lamp goes out; in the parallel circuit the other lamp keeps glowing.

Questions

1. Why are the lamps in a home connected in parallel?
2. What happens to the brightness if three lamps are connected in series?

Answers

1. In parallel each lamp gets the full voltage and glows at full strength. Each lamp can be switched on and off on its own, and when one lamp breaks, the others keep working.
2. The three lamps share the 6 V, so each gets only about 2 V instead of 3 V. All three glow even more dimly than the two lamps did.