Hertz: Definition & Concept

Instructor: Maria Howard

Maria is a teacher and a learning specialist and has master's degrees in literature and education.

Learn about the life of German physicist Heinrich Hertz and his contributions to our understanding of electromagnetic energy. Explore what a 'hertz' is and how we use it as a unit of measurement.

Proving Electromagnetic Energy Exists

I cannot tell you how much more satisfaction it gives me to gain knowledge for myself and for others directly from nature, rather than merely learning from others and for myself alone. -Heinrich Hertz

German physicist Heinrich Hertz was the kind of kid who was always tinkering and trying out different experiments at home. As a teen, he even built his own spectroscope, an instrument used to measure light. It's not surprising then that as a physics professor at the University of Bonn, Hertz started performing experiments looking at how electric sparks behave.

When he created a spark between two conductors, Hertz observed how another set of sparks materialized at the same time and soon began measuring these 'side sparks.' He was able to prove that the second set of sparks were electromagnetic energy, confirming what other scientists had only theorized about.

This German stamp commemorates the 100th anniversary of the year Hertz was born.
Image of Heinrich Hertz

Electromagnetic Waves

Hertz's experiments on electromagnetic energy revealed a lot about how this type of energy moves. Electromagnetic (EM) energy travels in a straight line in invisible waves that can bend around an object and be focused in a single spot like light--which makes sense, because visible light is one type of electromagnetic energy.

EM waves are transverse waves, or S-shaped, with a top curve called the crest and a bottom curve called a trough. We measure a wave by its wavelength, or the distance between the peak of one crest and the peak of the next. One wavelength is also called a cycle.

This diagram of a transverse wave shows how we measure one wavelength.
Diagram of a transverse wave

Hertz: The Number of Waves Per Second

We also measure the number of cycles (wavelengths) per second to determine a wave's frequency, and this also gives us an idea about the level of energy being transmitted. Frequency is measured by a unit called hertz (Hz), named in honor of Heinrich Hertz.

Hertz and the Electromagnetic Spectrum

We organize electromagnetic energy based on wave frequency in an electromagnetic spectrum. The higher the frequency, the more powerful the energy the electromagnetic waves give off. The spectrum is organized in seven bands, ranging from the slow waves Hertz first discovered, which we now call radio waves (low frequency), to the very powerful gamma rays emitted during nuclear explosions on the other end (high frequency).

The numbers at the bottom of this electromagnetic spectrum represent the frequency (hertz) for each part of the spectrum, with the exponent next to the ten representing the number of zeros the frequency has. For example, 10^6 stands for 1,000,000 Hz.
Diagram of the electromagnetic spectrum

The very weakest electromagnetic waves, radio waves, have a frequency of 30,000 Hz, and they only get faster and stronger as you continue along the spectrum, all the way up to 3 billion Hz. Since it's difficult to keep track of such large numbers, we use kilohertz (kHz), which is the unit representing 1,000 hertz. Just like we use kilometers to measure longer distances, 30,000 Hz becomes the far less clunky 30 kHz. In addition to kilohertz, radio waves are also measured in megahertz, or millions of waves per second. The strongest waves in the radio wave band of the EM spectrum measure as fast as 3 gigahertz (GHz), which stands for 3 billion hertz.

The next section of the spectrum, microwaves, has frequencies ranging from 300 MHz to 300 GHz. (If you notice some overlap between the frequencies of radio waves and microwaves, that is because there are no a hard lines separating the different bands; think of them as guidelines, not rules.)

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