Question

Which of the following is a device that increases or decreases the voltage of an alternating current

Answer 1

A transformer is able to increase or decrease the voltage of an AC source.

Answer 2

Remember, it all comes back to V=IR and P=IV. If you want to increase the distance traveled through wires (like water) you have to step up the voltage (i.e. pressure/potential), then when you don't need the electricity to travel great distances, you step down the voltage to increase the current, and decrease the resistance.