Final answer:
The voltage produced by a generator alternates because it operates similarly to an AC motor in reverse, with the mechanical rotation of wire loops in a magnetic field generating a sinusoidal emf which, in turn, drives an alternating current.
Step-by-step explanation:
The voltage produced by a generator alternates because it is essentially an AC motor in reverse. Electric generators contain wire loops within a magnetic field, and when these loops are rotated—typically by mechanical energy such as a turbine being turned by wind, water, or steam—the motion induces an alternating current (AC) electromotive force (emf). The voltage generated follows a sinusoidal pattern, meaning it rises and falls in a smooth, wave-like manner. This pattern creates the alternating direction of current flow, known as AC current, which means the voltage produced by a generator alternates because it produces a current that changes direction periodically.
In this process, the rotation rate and other factors such as the strength of the magnetic field affect the resulting emf. As a wire loop rotates at a constant angular velocity within a uniform magnetic field, the generator produces a voltage that varies sinusoidally over time. This is why generators are similar to motors in their construction but operate in a reversed manner: where a motor uses electrical energy to produce motion, a generator uses motion to produce electrical energy.