Question

For the holiday season, lights will be strung along each side of the walkway. If one box of lights will cover 10 feet of walkway, how many boxes are needed? Explain how you got your answer.

Answer 1

Older holiday light strings go dark if one bulb burns out, with each bulb normally having 3 V. Newer strings with short-circuit bulbs stay lit at about 3.08 V per bulb if one fails. In a series circuit, a 60 W bulb will be brighter than a 100 W bulb due to having higher resistance.

Step-by-step explanation:

When holiday lights are wired in series and one bulb burns out, the outcome depends on the design of the bulb. In older versions with bulbs that act like an open switch, if one burns out, the entire string goes dark because the electrical circuit is broken. When a string of 40 identical bulbs operates on 120 V, the normal operating voltage of each bulb is 120 V ÷ 40 = 3 V per bulb.

For newer versions with bulbs that act like a closed switch when they burn out, the rest of the bulbs remain lit, but they will have a higher voltage across each due to one less bulb in the circuit. If one burns out from a string of 40, leaving 39 bulbs, the operating voltage of each of the remaining bulbs becomes 120 V ÷ 39 ≈ 3.08 V per bulb.

Regarding the two household lightbulbs rated 60 W and 100 W connected in series, the bulb with the larger resistance will be brighter, which paradoxically will be the 60 W bulb due to it having a higher resistance than the 100 W bulb when operated at the same voltage.