What is the name of the device that increases voltage in a circuit?

The device that increases voltage in a circuit is called a step-up transformer. This transformer is specifically designed to increase the voltage from the primary coil to the secondary coil, which is essential in applications where higher voltage levels are needed for efficient power transmission or operation of electrical devices.

In a step-up transformer, the turns ratio between the primary and secondary windings determines the voltage increase. If the secondary coil has more turns than the primary, when an alternating current passes through the primary coil, a magnetic field is created, inducing a higher voltage in the secondary due to the greater number of turns.

The other options represent different electrical components that serve distinct functions: a step-down transformer reduces voltage, an inductor stores energy in a magnetic field when current flows through it, and a capacitor stores energy in an electric field. Each of these components plays a unique role in electrical circuits but does not perform the function of increasing voltage like a step-up transformer.