Friday is here again, and with it the weekly "A Taste of Physics" column — number 31.
This week: the color properties of neodymium, dichroism, and a surprising connection to electric vehicles.
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In the video you can see a glass clown figurine that changes color depending on the type of light directed at it.
The element neodymium is mixed into the glass from which it is made.
Neodymium cannot be found in nature in its pure form — it must be refined from various mineral mixtures, a fact that makes it expensive to produce.
Neodymium has a property called "dichroism," meaning it changes color by absorbing certain wavelengths of light and transmitting the remaining ones.
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The way neodymium's electrons are arranged around the atomic nucleus causes it to absorb only wavelengths in the blue and violet range.
This means those wavelengths of incoming light are absorbed, and the color visible to the eye is produced by the wavelengths that were *not* absorbed — the ones reflected or transmitted through the material.
The more the spectrum of the original light source leans toward red wavelengths, the more of them will be re-emitted, giving the glass a reddish hue.
Fluorescent light, for example, has a spectrum that skews entirely toward blue, so even after some wavelengths are absorbed, the glass still appears greenish.
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Neodymium is widely used in industry.
Its light-absorption properties are valuable in the laser industry, because it emits coherent light waves.
It is also used to create exceptionally powerful magnets, and is therefore incorporated into products such as computer components and headphones.
Neodymium plays a critical role in building high-performance electric motors — which is why every electric vehicle motor contains more than a kilogram of neodymium.
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One more interesting detail to close with.
You may actually encounter neodymium on the beach, in the form of smooth, color-shifting pieces of sea glass.
In the 20th century, glassware and crystal companies such as the Czech manufacturer Moser began making extensive use of neodymium to color their pieces.
Over the years, these items found their way into the ocean, where they shattered into fragments and underwent prolonged weathering that gave them their characteristic smooth, frosted appearance.
Next time you pick up a piece of sea glass like that, try to imagine the factory worker on the production line who colored it with neodymium so many years ago.
Shabbat Shalom 😊
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