Video: Identifying Sources of Infrared Radiation

Which of the following could be a source of infrared radiation? [A] Alternating electric currents [B] Decaying atomic nuclei [C] Direct electric currents [D] Thermal motion of atoms and molecules [E] None of the answers is correct.

02:50

Video Transcript

Which of the following could be a source of infrared radiation? A) Alternating electric currents, B) decaying atomic nuclei, C) direct electric currents, D) thermal motion of atoms and molecules, E) none of the answers is correct.

We see that each one of the options A through D is a candidate for being a source of infrared radiation, a particular type of radiation in the electromagnetic spectrum. As we consider which of these four options could be a source of IR, infrared, radiation, let’s start out up at the top with option A, alternating electric currents.

When alternating electric currents are used to generate electromagnetic radiation, what is typically produced from this source is either microwaves or radio waves. This is because the frequency of oscillation of these currents is low enough that it produces these particular types of radiation. We see that not only option A talks about electric currents, but so does option C, but this time in the form of direct electric currents, that is, currents that always move in the same direction.

Even though direct currents do always move the same way, we can effectively turn them into alternating currents by switching these direct currents on and off over and over again. It’s by this mechanism that radio waves can be created. What we’re seeing is that both of these options, alternating as well as direct electric currents, do act as sources for electromagnetic radiation, but not sources for infrared radiation. Instead, they’re typically used to create microwaves and radio waves. So we’ll cross those off our list of options.

Moving on to option B, decaying atomic nuclei, this is a process where an atomic nucleus splits or breaks apart into smaller pieces — that’s called fission — and in the process releases energy through electromagnetic radiation. But the type of radiation typically emitted through this process is gamma radiation, that is, the emission of gamma rays. So once more, this option is a source for a particular type of electromagnetic radiation, but not the type we’re interested in, infrared radiation. So we cross option B off our list too.

Next, we get to option D, the thermal motion of atoms and molecules. Here’s what this option means. Everyday objects such as chairs, tables, and the like, simply by being at room temperature, about 20 degrees Celsius or about 70 degrees Fahrenheit, has enough thermal energy that the atoms and molecules in these objects are in thermal motion. And thanks to this thermal motion, a particular type of radiation is emitted. And this indeed is infrared or below-red radiation. That is, our eyes aren’t sensitive to this particular wavelength of radiation. But nonetheless, it’s there and it’s created by thermal motion of atoms and molecules. This option can be a source for infrared radiation. And therefore, option E that none of the answers is correct is itself not correct. And so our final answer is that thermal motion of atoms and molecules could be a source for infrared radiation.

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