Final answer:
A straight, horizontal rod sliding along parallel conducting rails forms a closed circuit. The rod and the rails provide a complete path for electric current to flow. If the rod moves through a magnetic field, it can induce a current in this circuit.
Step-by-step explanation:
The straight, horizontal rod sliding along parallel conducting rails forms a closed circuit. This happens as a consequence of the rod, which can be considered as a conductor, and the rails, being made of an electrically conductive material, establish a complete electrical path for the current to flow.
Consider for instance the premise of Faraday's law which explains that moving a conductor, such as a rod, through a magnetic field induces a current in that conductor if it is part of a closed circuit. One way to visualize this is to imagine the rails as wires connected to a battery, and the rod as a wire completing the loop. If the rod moves, it can induce a current according to Faraday's law, only if it forms a closed circuit. If the rod was removed, a circuit will not be completed and no current would flow, illustrating conceptually a difference between open circuits and closed circuits.
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