Final answer:
Wires are attached to both ends of the rear defroster's metal strips to allow electric current to flow, heating up the strips. In a car's electrical system, one battery terminal connected to the chassis allows the use of a single wire to complete a circuit with electrical devices. Lights may dim when starting engines due to temporary voltage drops.
Step-by-step explanation:
Wires are attached to both ends of the metal strips in a car's rear defroster to create a complete electrical circuit. This allows current to flow through the strips, causing them to heat up and defog or defrost the rear window.
Regarding the car's electrical system, when one battery terminal is connected to the metal body of the car, it acts as a ground. This means that only a single wire is necessary to supply current to electrical devices, as the car's body completes the circuit back to the battery's other terminal. This configuration simplifies the wiring system and saves on material costs.
Experiencing the lights dimming when starting the engine is due to a temporary drop in voltage caused by the increased demand on the battery. When high-current devices turn on, like a car engine or a refrigerator compressor, the initial surge can cause other devices in the circuit to momentarily receive less power, thus dimming the lights.