Video: Electromagnetic Waves and Matter

Which of the following types of electromagnetic radiation has the strongest interaction with matter? [A] Visible [B] Infrared [C] Gamma [D] X-ray [E] Radio

04:13

Video Transcript

Which of the following types of electromagnetic radiation has the strongest interaction with matter? A) Visible, B) Infrared, C) Gamma, D) X-ray, or E) Radio.

To answer this question, the first thing we need to know is the difference between these types of radiation. Now, we know that they’re all types of electromagnetic radiation. Or, in other words, they’re all types of electromagnetic wave. So in that sense, they’re all actually very similar to each other. They’re all examples of the same physical phenomenon. But the difference between them is that they all have different wavelengths.

We represent wavelength with the Greek letter 𝜆. And, as you may’ve guessed, wavelength tells us the physical length of a wave. In other words, it tells us the distance over which a wave completes a full cycle. So, in this example, the wave at the top has a much larger wavelength than the wave at the bottom.

Now, when it comes to electromagnetic radiation, the wavelength is really important because it relates directly to the amount of energy that each wave has. In fact, the shorter the wavelength, the more energy an electromagnetic wave has. So, in our example, the top wave has a relatively big wavelength. And the bottom wave has a relatively small wavelength. This means that the bottom wave has more energy than the top wave.

In fact, in this example, we can see that the bottom wave has half the wavelength of the top wave. That means that, in the same distance that the top wave would complete one cycle, the bottom wave completes two cycles. The relationship between the wavelength of a wave and the amount of energy it has is actually such that halving the wavelength will double the amount of energy that it has. So in this example, the bottom wave will actually have two times as much energy as the top wave.

So to answer this question, all we actually need to know is which type of radiation has the shortest wavelength because the one with the shortest wavelength will have the most energy. So it will have the strongest interaction with matter. A good thing to have in our heads at this point is an idea of what the electromagnetic spectrum looks like. The electromagnetic spectrum is just a way of organizing electromagnetic waves in order of their wavelength. So let’s see how we could draw this. Let’s put waves with small wavelengths on the left. And as we move to the right of our diagram, we will increase the wavelength of the waves so that we have medium wavelengths in the middle and really big wavelengths over on the right.

Most diagrams of the electromagnetic spectrum will go from wavelengths of around 10 to the power of negative 12 meters, which is around 100 times smaller than an atom, up to about 10 to the power of four meters or 10 kilometers. So this covers an absolutely huge range although it is still possible to have waves that have a larger wavelength than 10 to the power of four meters or a smaller wavelength than 10 to the power of negative 12 meters.

Now, all electromagnetic radiation is categorized according to its position on the electromagnetic spectrum. In other words, it’s given a name to describe roughly how long its wavelength is. Starting on the right of our diagram, the waves with the largest wavelengths are categorized as radio waves. Next are microwaves with a slightly shorter wavelength than radio waves. Next is infrared radiation or IR. Then, in the middle, we have visible light, which is all the wavelengths that we can see. Next is ultraviolet or UV radiation, then X-ray. And finally, the category of radiation with the shortest wavelengths is gamma.

So, because shorter wavelengths have more energy, the electromagnetic spectrum not only organizes waves by wavelength, but by the amount of energy that each wave of a certain type has. Over on the right of the electromagnetic spectrum, we have waves with the biggest wavelengths. So each wave of this type will have the least amount of energy. And it will have the weakest interaction with matter. Whereas over on the left-hand side, we have waves with the shortest wavelengths. So they have the most energy and therefore the strongest interaction with matter.

So the correct answer to this question is C. The type of electromagnetic radiation that have the strongest interaction with matter is gamma.

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