In a parallel circuit, what is applied simultaneously across all devices?

In a parallel circuit, all devices connected in the circuit experience the same voltage across their terminals. This configuration allows each device to operate independently, with its own potential difference applied directly across it. The voltage remains constant and equal across all components, regardless of the individual resistances of each device.

This is a fundamental characteristic of parallel circuits, making them distinct from series circuits, where the same current flows through all components but the voltage can differ across each device based on their resistances. The ability to maintain the same voltage across all devices in parallel circuits is crucial for evenly distributing power and ensuring that devices function as intended without interference from one another.

With this understanding, it becomes clear that the applied voltage is what remains constant across all elements in a parallel circuit.