### Video Transcript

What is the name of the type of electromagnetic radiation that has the lowest frequencies?

Okay, so, this question is specifically referring to the electromagnetic spectrum. So, let’s start by recalling that the electromagnetic spectrum consists of the entire range of electromagnetic waves possible, from the longest wavelength all the way to the shortest wavelength. Now we can also recall that electromagnetic waves travel at the speed of light.

Speed of light is a constant which we often denote with the letter 𝑐. And we can recall that the speed of light 𝑐 is given by multiplying the frequency of the electromagnetic wave multiplied by the wavelength of that particular electromagnetic wave. And so, we’ve now got the relationship between the speed of light, which is a constant, the frequency of an electromagnetic wave, and the wavelength of the electromagnetic wave.

And in fact, if we rearrange this equation, so that we can say that the frequency of an electromagnetic wave is equal to the speed of light divided by the wavelength, then we can see that, once again, because the speed of light is a constant, that the frequency of an electromagnetic wave is inversely proportional to its wavelength. In other words then, the larger the wavelength of an electromagnetic wave, the smaller the frequency, and vice versa.

So, if we’re looking for the electromagnetic waves which have the lowest frequencies, then by this inverse relationship we’re also looking for the electromagnetic waves with the highest wavelengths. And we can actually recall that the electromagnetic waves with the largest wavelengths are known as radio waves.

We can recall that the rest of the EM spectrum in order of increasing frequency, or decreasing wavelength, goes as follows. Shorter wavelength than radio waves are microwaves, then infrared rays, then visible light, then ultraviolet light, then x-rays, and then finally gamma rays. But we’re specifically looking at the waves which have the lowest frequencies, so that’s radio waves.

Now any electromagnetic waves with a frequency of less than about three times 10 to the power of nine hertz are known as radio waves. And equivalently, we can say that radio waves have wavelength above about 0.1 metres. And so, we can say as the answer to our question that the name of the type of electromagnetic radiation that has the lowest frequencies is radio waves.