Which electrical device is utilized to increase line voltage?

The transformer is the device specifically designed to increase (or decrease) line voltage while maintaining power at a constant level. It operates on the principle of electromagnetic induction, allowing for the transfer of electrical energy between two or more circuits through inductively coupled conductors—the transformer's coils.

When used to increase voltage, known as a step-up transformer, it has more turns of wire in the secondary coil than the primary coil. This configuration allows the input voltage to be raised to a higher output voltage, making transformers essential in power distribution systems where electricity is transmitted over long distances at high voltages to minimize losses.

In contrast, a capacitor stores and releases electrical energy but does not inherently increase voltage; instead, it affects the current and voltage phase relationships in AC circuits. A resistor, on the other hand, is used to limit current flow and does not change voltage levels. An inductor also stores energy in a magnetic field and can affect current and voltage but does not serve the primary purpose of voltage increase. Thus, the transformer stands out as the correct choice for increasing line voltage in electrical systems.