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Understanding Extremely Low Frequency Waves

A kilometre (km) is a unit of length equal to 1,000 metres, and in the context of electromagnetic waves, it is used to describe extremely long wavelengths, typically in the Very Low Frequency (VLF) and Extremely Low Frequency (ELF) ranges. These wavelengths correspond to very low frequencies, usually below 300 kHz, and are commonly used in long-distance radio communication, submarine communication, navigation systems, and geophysical research.

For instance, a frequency of 30 kHz has a wavelength of 10 km, while 3 kHz corresponds to a wavelength of 100 km. These long wavelengths can travel great distances, penetrate seawater, and diffuse around obstacles, making them ideal for communication with submerged submarines and in areas where traditional signals cannot reach. ELF waves, with wavelengths of hundreds to thousands of kilometres, are also used in Earth monitoring, such as detecting seismic or lightning activity.

Using kilometres to measure wavelength allows scientists and engineers to understand and design systems for global communication and natural signal monitoring. Although challenging to generate and detect, kilometre-scale wavelengths play a vital role in specialized but critical applications.

The Fundamental Unit of Frequency

The hertz (Hz) is the standard unit of frequency in the International System of Units (SI), defined as one cycle per second. It measures how often a repeating event occurs each second, making it a fundamental concept in physics, engineering, and many branches of science.

Frequency measured in hertz is essential for understanding waves and oscillations, including sound waves, electromagnetic waves, and mechanical vibrations. For example, in acoustics, the pitch of a sound corresponds directly to its frequency in hertz—middle C on a piano has a frequency of about 261.6 Hz.

In electrical engineering, hertz measures the frequency of alternating current (AC), with common household power typically operating at 50 or 60 Hz depending on the country. Radio and television broadcasting frequencies, as well as wireless communication signals, are also expressed in hertz and its multiples.

Because hertz represents a single cycle per second, it serves as the base unit from which all other frequency units are derived, including kilohertz, megahertz, and gigahertz. Understanding frequency in hertz allows scientists and engineers to design and analyze systems ranging from audio equipment to complex telecommunications networks.