Final answer:
Lights in houses are wired in parallel to use the full voltage source and operate independently. In series, if one light bulb fails, the rest go out like an open switch. For two bulbs with different wattage ratings connected in series, the one with more wattage will be dimmer since it has a lower resistance and receives less voltage.
Step-by-step explanation:
In a house, lights are wired in parallel instead of series because this allows them to utilize the full voltage of the source and operate independently. If one light burns out, it doesn't affect the other lights in the circuit. In contrast, when lights are wired in series, like in some strings of holiday lights, if one bulb burns out it breaks the circuit - like an open switch - causing all other bulbs to go out too. With 40 identical bulbs on a 120 V line, each bulb operates at 3 V normally. In newer versions of holiday lights, if one bulb short circuits, the rest of the bulbs continue to operate, but with a slightly higher voltage across each because there are now only 39 bulbs in series on the 120 V line, resulting in approximately 3.08 V across each remaining bulb.
Regarding household lightbulbs connected in series, a 60 W and a 100 W bulb would have different brightness levels because they are designed to operate at the same voltage, not in series. When connected in series, the 100 W bulb will be dimmer than if it were connected directly to the household power because in a series circuit the voltage across each component is divided based on its resistance, and the 100 W bulb has a lower resistance, thus getting less voltage in this setup.