Final answer:
Adding bulbs to a circuit generally decreases brightness due to increased resistance. In series holiday lights, a broken bulb causes all bulbs to go out or changes their voltage depending on the bulb design. Increasing a variable resistor's resistance in a lightbulb circuit results in redder light from the bulb. The correct option is b).
Step-by-step explanation:
The question pertains to the behavior of light bulbs arranged in a circuit and how their brightness or the current through them is affected by changes within the circuit.
Adding new light bulbs to an existing circuit typically decreases the brightness of the other bulbs due to the increased total resistance, which results in a lower current through the circuit if the voltage remains constant.
When holiday lights are wired in series and one bulb breaks, creating an open circuit, all the other bulbs will go out because the electrical path is broken.
If a string of 40 bulbs operates on 120 V, the normal operating voltage of each bulb is 120 V divided by 40, resulting in 3 V per bulb. If one bulb short circuits in a newer version, the remaining 39 bulbs will stay lit, and each will have a new operating voltage of 120 V divided by 39, which is approximately 3.08 V per bulb.
Adjusting a variable resistor in a circuit with a lightbulb changes the resistance and thus the current flowing to the bulb.
Increasing the resistance generally results in redder light from the bulb, as the decrease in current consequently decreases the temperature of the filament, and a cooler filament emits light with a longer wavelength or redder color. Option b) is the correct one.