Final answer:
The number of power sources for a contactor can vary, but typically one is used. For light bulbs with three power settings, at least two filaments are needed.
Step-by-step explanation:
The question regarding the number of power sources that need to be connected to a contactor can vary based on the design and purpose of the contactor circuit. Typically, a contactor is used to control an electrical power circuit with a lower power signal, often using a single power source for its operation. However, in specialized applications, the number could be more, but the provided options do not suffice to answer without additional context about the specific type of contactor.
Talking about light bulbs with multiple power settings, the minimum number of filaments required for three power settings (not including zero) would be two. This configuration allows the creation of three distinct settings by having one filament on for the first setting, the other filament on for the second setting, and both filaments on for the third setting.