Final answer:
Lights strung together in a line along a circuit are connected in a series circuit. If one bulb in an old series string burns out, the entire string goes out, whereas in newer versions, the remaining bulbs continue to light up.
Step-by-step explanation:
When lights are strung together in a line along a circuit, each light is connected to the next in a single path for the electric current to flow. This type of connection is called a series circuit. In a series circuit, the same current must pass sequentially through each light or resistor. If one light burns out in an older version of such a string, designed with bulbs that break the electrical connection like an open switch, the entire string goes out. Each bulb in a string of 40 bulbs operating on 120 V would have a normal operating voltage of 120 V divided by 40, which is 3 V per bulb. Conversely, newer versions of holiday lights are designed so that when a bulb burns out, it creates a short circuit, acting like a closed switch, and the remaining bulbs continue to light up. In that case, if one bulb burns out in a string of 40, leaving 39 bulbs, each of the remaining bulbs would operate at approximately 120 V divided by 39.