Try this: You see UV

Use these materials

Pour some tonic water into a jar
Pouring peroxide

Shine a UV light onto the jar

Warning: Although UV radiation is invisible to the human eye, blacklight bulbs are still bright light sources. Do not use them in a darkened room or use them for more than fifteen minutes a day.

You will need

  • UV Blacklight bulb (available from Jaycar Electronics, or other hobby stores)

  • Soda water

  • Tonic water

  • 2 identical jars with lids

  • A friend

What to do

  1. Pour soda water into a jar until it is nearly full.

  2. Pour tonic water into a jar until it is nearly full.

  3. Place both jars in front of a friend and ask if they can tell – without touching either of them – which jar contains tonic water, and which one soda water.

  4. Shine the UV blacklight on both jars and note which one glows blue. This one is the tonic water.

What’s happening?

Take a sip of the tonic water. Taste nice? No? Well, some people like that bitterness. The sharp bite of tonic water comes from ‘quinine’, a chemical extracted from the bark of the cinchona tree. Quinine has long been used as a treatment for malaria, and was once used in a wide range of medicines to treat a number of ailments. As such, it was the main ingredient in a lot of health tonics.
Quinine has a special property; it glows blue under ultra violet (UV) light. It does this by fluorescing.
To understand what this means, it helps to know that the wavelength of UV light is a little too short for the cells in our eyes to detect. Many other animals, such as bees, can see it quite easily. Fluorescence occurs when a particle absorbs some light of one wavelength and shoots out light of a slightly longer wavelength. In this case, the invisible UV light shining from the blacklight is absorbed by the quinine and turned into a form of light we can see.

Quinine under a UV light

Quinine changes UV radiation into a light blue light we can see
 

Applications

UV light falls into several catagories, of which blacklight UV (or UV-A) is the safest, falling just outside of the visible spectrum. Other forms of UV, however, can damage DNA. In the ocean, some animals make proteins that turn UV light into visible light, possibly as a form of sunscreen to shield them from the more dangerous forms of UV radiation.
Forensics officers often explore crime scenes using a blacklight. A number of bodily fluids will fluoresce as well, yet are otherwise invisible to the naked eye.
Some fluorescing chemicals can be stuck onto antibodies that will attach onto specific bits of a cell. If you look at the cell under the microscope using UV light, those parts can then be easily spotted. ‘Fluoro In Situ Hybridisation’ (FISH) is one technology that relies on fluorescence to locate specific bands of DNA on a cell’s chromosomes.

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