What does Hertz (Hz) measure?

Hertz (Hz) is a unit of frequency that quantifies the number of cycles per second of a periodic event. In the context of the question, it specifically measures how many complete cycles of a spinning magnet occur every second. This is particularly relevant in electrical engineering and physics, where electromagnetic waves and alternating currents are frequently discussed.

For example, in alternating current (AC) electricity, the frequency measured in hertz indicates how often the current changes direction per second, which in many parts of the world is typically 50 or 60 Hz. This unit is essential for understanding the behavior of various electrical systems and machines, particularly motors and generators that operate based on the principles of electromagnetic induction.

The other options address different concepts: the amount of electricity flowing through a circuit pertains to current, voltage refers to electric potential, and the speed of sound is relevant in acoustics, not in the context of hertz. Therefore, the correct answer accurately reflects the definition and application of hertz in measuring frequency.