A decorative holiday light string is designed for a 120 V household outlet. It contains four identical branches wired in parallel across the outlet. Each branch consists of five identical miniature filament bulbs connected in series. Each bulb is rated for safe operation at 30 V.
During operation, a student removes one bulb from Branch 3, leaving an open socket (an air gap) in that branch. Assume each bulb has an operating resistance of 240 Ω and that the resistance of removed or burned-out bulbs becomes effectively infinite.
(a) Explain qualitatively why every bulb in Branch 3 extinguishes immediately after the removal, yet the bulbs in the other three branches remain lit.
(b) Before the removal, the string draws a certain current from the outlet. Determine the power dissipated by a single bulb before the removal.
(c) After the removal, calculate the new total current drawn from the outlet and the new power dissipated by a bulb in any of the still-complete branches. Clearly state any assumptions made about how individual bulb resistance depends on temperature in this scenario.
(d) Discuss whether the bulbs in the intact branches appear brighter, dimmer, or unchanged compared with their brightness before the bulb was removed. Support your claim with energy or circuit reasoning tied to your calculations.