Testing sunscreen, an activity for grade 8

Thanks to Adam, the idea was his. It is based on the fact that tonic water contains quinine which fluoresces under ultraviolet light.

Tonic water (L) and tap water (R) lit by an insect electrocuter

This is a learning activity for grade 8 kids. Its intended outcomes are:

• Safe behaviour relating to sun exposure
• ie. declarative knowledge about SunSmart behaviour which is applied in daily life
• Declarative knowledge about sun exposure and health
• Declarative knowledge about the spectrum and ultraviolet
• Scientific method
• Experimental design
• Problem solving

http://commons.wikimedia.org/wiki/Image:Regenbogen_%28NASA%29.jpg

Requirements, tonic water, tap water, 2 glasses, glass plate, sunscreen : no screen, low SPF, SPF30+. Sunlight and incandescent light but MUCH better with a UV source like an insect killer.

This is a lesson based on guided discovery by the kids.

LESSON
Hi kids, what do you know about SunSmart ?
Prompt the kids as required, they should be able to quote the key messages:

• Slip - Clothing
• Slop - Sunscreen
• Slap - Hats
• Seek - Shade
• Slide - Sunglasses

Why do you do this?
Prompt till you elicit that sun exposure can cause health effects including skin cancer.

What is it about sunlight that does this?
Question their understanding further and elicit or explain that UV rays are the reason and that they are part of the spectrum and "more purple than purple" and hence invisible.

Hey kids, we have this really neat way of testing for ultraviolet light, the quinine in tonic water glows blue under ultraviolet light. Pour a glass of tonic water and tapwater, under sunlight there is a faint blue colour.

How do we know that the ultraviolet is making the blue colour and its not just blue water?
Wait for suggestions...
Would a different light be a way to test?
If you are lucky they will suggest artificial light. Chose incandescent lighting, well away from windows. Not fluorescent lighting, it contains UV. The blue colour is absent or very faint. At this point the kids should be convinced that a characteristic of sunlight causes the blue colour.

If you are lucky you will have an insect electrocuter or other blacklight source.
Kids, can you suggest anothe light source? Move to UV source. Wow it is really amazing!

OK kids we have 3 samples of sunscreen we want to test, any suggestions?
Typically they will suggest dissolving the sunscreen in the water, if you have time, try it, we didn't. Then they will suggest smearing it on the glass. We had a glass plate which we hinted at its use by looking hopefully at it, the kids got the hint and designed the experiment.

Glass plate smeared with 3 unidentified products, the kids were able to correctly identify moisturiser, SPF15 and SPF30