Final answer:
Staircases with more than six steps require switches at both ends for safety and convenience. A minimum of two filaments are needed for a light bulb to have three power settings. In a series-wired light string, if an old bulb that breaks the circuit burns out, all bulbs go out; if a newer bulb that shorts out burns out, remaining bulbs stay lit with a slight increase in voltage.
Step-by-step explanation:
Staircases of more than six steps should have a switch at both ends to ensure lighting can be managed safely from either end of the staircase. This is to provide convenience and enhance safety, allowing the lights to be turned on or off from the top or bottom of the stairs. When staircases are designed, certain electrical characteristics such as current flow (I(F)), cable type (e.g., 3G1 Cu), and power (P), are considered to ensure the lighting system operates efficiently without overloading the electrical circuit. For instance, if we're using 120W for each lighting circuit on the staircases.
When it comes to light bulbs with three power settings, the minimum number of filaments required is two. These filaments would be individually switched and wired in parallel, thus allowing for three different power settings - one for each filament separately and one with both filaments on. This configuration facilitates having a low, medium, and high brightness setting.
For series-wired strings of holiday lights, if one bulb in an old version that breaks the connection when it burns out fails, then all the other bulbs will go out because the electrical circuit is interrupted. Each bulb in a string of 40 would normally operate at a voltage of 3 volts (120V/40 bulbs). If a newer bulb that is designed to short circuit when it burns out fails, the other bulbs would remain lit, and the voltage across each of the remaining 39 bulbs would slightly increase to approximately 3.08 volts (120V/39 bulbs).