Science Buddies: "Ask an Expert"

We want to see if the higher SPF sunscreen blocks more UV radiation. Should we use the UV index reading as the dependent variable? Or should we use the mW/m2 reading that our little UV checker also has on the screen. The UV index reading is just a range, so it seems like the results will be more valid if we use the mW/m2 reading.....please help! THANKS!

Hi Amanda,

Welcome to Science Buddies.

Are you doing this excellent project? https://www.sciencebuddies.org/science- ... p015.shtml

If you are doing this project, or something similar, the sunscreen with its UV index rating is the independent variable. The UV reading from the UV monitor is the dependent variable.

Here is a link with more information on variables:

https://www.sciencebuddies.org/science- ... test.shtml

After you collect your data, you will be graphing your results, with the UV index of the sunscreen on the x axis and the UV reading of the monitor on the y axis.


https://www.sciencebuddies.org/science- ... ysis.shtml

Please let us know if you have more questions.


Donna

Thank you! We are just not finding much variation of the UV index readings. So I thought this other reading (the mW/m2 number which I think is the UV irradiance reading) would be more accurate.
But we will stick to the UV index level!

THANK YOU! THANK YOU!

Hi Amanda,

If you are not finding much variation in the UV reading vs the UV index rating of the sunscreen, you might try expanding the scale of the x-axis to see if this will make any difference in how the graph looks.

Otherwise, you will have the most interesting discussion section on the project board. You will need to decide if the lack of variation in results was due to the sunscreens themselves (did you use sunscreen with recent dating), or to the UV monitor you were using. The UV monitor may be giving accurate, but not precise results. What happens when you measure a sample three times in a row? Does it give the same reading every time? If is does, then the results are precise and reproducible. Did you see any difference between no sunscreen and a product with a high rating? If not, then the problem may be due to the precision of the UV monitor.

Here's a website that has more information on these concepts:

http://chemistry.about.com/od/unitsconv ... cision.htm

You might also want to do more research on your UV monitor and make sure it was designed for measuring your samples.

In the last paragraph of your conclusion, you should state what you would do to resolve the question if you were to do the experiment again.

Please let me know if you have questions.

Donna