Question Video: Electromagnetic Waves and Matter Physics

Video Transcript

One or more of the following types of electromagnetic radiation contain at least some wavelengths that are ionizing. Which of these types can or must be ionizing, a) ultraviolet, b) infrared, c) microwaves, or d) X-rays?

So in this question, we’re trying to work out the types of electromagnetic radiation that can or must be ionizing. So what is ionizing radiation in the first place? Ionizing radiation is defined as any form of electromagnetic radiation above a certain threshold energy. This threshold energy is when radiation first starts being ionizing. Who would have thought?

Basically this refers to when the electromagnetic radiation can enter a human body and start ionizing the cells in that body. So any radiation above the threshold energy can ionize cells in the human body. So in order to answer this question, we can draw a diagram showing the electromagnetic spectrum increasing in energy.

And here’s our diagram. Starting with the waves which have the lowest energy, we’ve got radio waves. Then we’ve got microwaves, which have slightly more energy. Then we get to infrared, then visible light, then ultraviolet, then X-rays, and then finally gamma rays. Now each one of these fall in a certain range. These energy ranges are not equally divided up as we’ve drawn in the diagram here. But that’s not super relevant.

All that matters is that we know where the threshold energy is. Now the threshold energy that we’ve discussed for ionization is defined at being roughly near the very top end of the ultraviolet part of the spectrum. That means that anything above this energy is known as ionizing radiation. In other words, some types of ultraviolet rays, the very high-energy ones, as well as all of the X-rays and all of the gamma rays are known as ionizing radiation.

Now the question is asking us which of the four types of radiation that we’ve been given can or must be ionizing. So let’s go through each one, starting with a) ultraviolet. Well as we’ve already discussed, some forms of ultraviolet can be ionizing. So this is an answer to our question. b) infrared, well infrared falls around here so it’s below the threshold energy.

Therefore, infrared cannot be an answer to our question. c) microwaves, the same is true for microwaves. They fall below the threshold energy. And d) X-rays, yes as we’ve seen earlier X-rays do fall into the ionizing radiation category. And so the final answer to our question is that ultraviolet rays can be ionizing and X-rays must be ionizing.