In the United States, what is the normal number of AC cycles per second?

In the United States, the standard frequency for alternating current (AC) electricity is established at 60 cycles per second, commonly referred to as 60 Hertz (Hz). This frequency is significant because it allows for the consistent operation of electrical appliances and systems, ensuring they function efficiently and reliably.

The 60 Hz standard was adopted in the early 1900s and has since become the benchmark for residential and commercial electrical systems across the country. This frequency is ideal for the generation and transmission of electricity, as it strikes a balance between efficiency and ease of use for a wide variety of electrical devices.

Understanding that the other options represent frequencies that are not standard in the U.S. context helps to further clarify why 60 cycles per second is the correct choice. Frequencies like 30 Hz, 45 Hz, and 75 Hz are uncommon for general residential and commercial power distribution in the U.S. Each of these frequencies may have specific use cases in different contexts or countries, but for general AC power supply, 60 Hz remains the established norm.