I don't think that ultraviolet light, are invisible waves because there's a device that check whether the money is true or fake. by aiming the uv light through it.. and it is visible by naked eye.

how this happen?

Note by Reginald Pilar
4 years, 3 months ago

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Reginald, like you said, there is light that's visible to the naked eye when UV light is aimed at marked money. But, can you see the UV light when the money isn't there?

What happens is the UV photons hit a strip of ink in the money that has so-called UV fluorescence. That means there are some molecules in the ink that can absorb photons in the UV part of the spectrum. These absorbed photons kick the ink molecules into a temporary excited state, then the molecule relaxes back to the ground state, and releases some of the energy from the UV photons in a photon of longer wavelength. That longer wavelength photon is in the visible spectrum, the light you observe with your eyes.

That might sound like the conservation of energy has been violated. After all, how can the released photon be of a lower energy than the incoming photon? Some of the energy ends up being dissipated by some other process such as heat or driving a chemical reaction.



For instance, when cells are imaged, they usually need to be "quenched" by some reactive chemical species This is the mechanism by which the incoming photon becomes visible. It goes in, and emerges with some of its energy stolen to heat.

Josh Silverman Staff - 4 years, 3 months ago

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