Video Transcript
Which of the following could be a source of ultraviolet radiation? (A) Decaying atomic nuclei. (B) Thermal motion of atoms and molecules at room temperature. (C) Alternating electric currents. (D) High-speed electrons impacting on a metal plate. (E) None of the answers is correct.
Here, we have four physical processes described. And we want to figure out which one, if any, could be a source of ultraviolet radiation. Ultraviolet radiation is radiation within a certain range of wavelengths. These wavelengths correspond to a particular range of energies. So, if any of these physical processes release energy within that particular range, they could be a source of ultraviolet radiation. Starting with answer choice (A), when atomic nuclei, the cores of atoms, decay, energy is indeed released. But so much energy is released that this corresponds to a type of radiation called 𝛾 rays. 𝛾 rays are much higher energy than ultraviolet radiation. We won’t choose then answer option (A).
The thermal motion of atoms and molecules at room temperature also releases energy in the form of electromagnetic radiation. But this type of radiation is called infrared radiation. Note that this answer option specifies that these are atoms and molecules moving around at room temperature. As an interesting side note, this means that at this temperature, all objects are sources of light, specifically of infrared radiation. In any case, we won’t choose answer option (B) because infrared is not the same as ultraviolet radiation.
Next, answer choice (C) purports that alternating electric currents may be a source of ultraviolet radiation. We can recall though that AC circuits are rather a source of microwaves and radio waves. For example, alternating electric currents are the means by which radio antennas transmit radio signals. Radio and microwaves have much less energy than ultraviolet radiation.
We move on then to answer choice (D). When high-speed electrons impact or collide with a metal plate, enough energy is released that the resulting radiation is called an X-ray. On the electromagnetic spectrum, X-rays and ultraviolet radiation are right next to one another. Nonetheless, X-rays are higher energy than ultraviolet rays. So we won’t say that this process that generates X-rays is also a source of ultraviolet radiation.
This leaves us with answer choice (E) that none of our answers is correct, and indeed we find this to be true. Of these possible sources of ultraviolet radiation, none of them is an actual source. None of the answers is correct. So we choose answer choice (E).
