Video Transcript
The following figure shows a continuous range of wavelengths of electromagnetic radiation. A part of this range that corresponds to visible light is shown within the red-dashed box. Which of the following types of electromagnetic radiation could correspond to the electromagnetic radiation shown within the solid blue box? (A) Ultraviolet, (B) infrared, (C) radio.
We can see in our figure that our continuous range of wavelengths starts out very small; that is, the wavelengths at this end are quite short, and then they get longer and longer as we move left to right across our figure. We also see the range of wavelengths highlighted here corresponding to visible light and then this range of wavelengths just to the right of that. We can imagine that this figure represents wavelengths in the electromagnetic spectrum. Clearing some space on screen, we can arrange this representation of the spectrum by putting shorter wavelengths to the left and longer wavelengths to the right. There are seven categories we could call them of this spectrum.
The shortest-wavelength radiation are called 𝛾 rays, then come X-rays, then ultraviolet radiation, then visible light, then infrared radiation, or IR for short, followed by microwaves, and finally radio waves with the longest wavelengths of all. In our question, we’re asked to identify which of these three types of radiation corresponds to that identified in this blue box. Since visible light is right here and on our spectrum, ultraviolet radiation is to the left of visible light — that is, it has a shorter wavelength — we know that our answer can’t be option (A). Noting that this blue box highlights wavelengths that are longer than those of visible light, we can see on our spectrum that both infrared and radio waves are to the right, that is, have a longer wavelength than visible radiation.
Notice though that infrared radiation has a wavelength much more like that of visible light than radio waves do. In order for this solid blue box to highlight radio waves consistent with answer choice (C), we would have to say that in the space between these highlighted boxes there’s infrared as well as microwave radiation. Based on the similarity, though, between the wavelengths in these two boxes, it’s much more likely that those represented in the solid blue box are infrared radiation, since radio waves have a much larger wavelength than visible light.
Therefore, we choose answer choice (B). Infrared radiation could correspond to the electromagnetic radiation shown within the solid blue box.
