Science fair

[DeepalS]

Hello, my name is Deepal Sanghrajka and I am in 7th grade. I have been conducting a science fair project and need some suggestions. My project is called Protection from ultraviolet light. My question is "Which sunscreen(SPF 15, SPF 30, or SPF 50) is best at blocking out ultraviolet rays?". My hypothesis is that the SPF 50 sunscreen will block out the most ultraviolet rays because its SPF is higher.

This is what I did for this experiment:
1. Pour liquid aagar into four petri dishes and let it solidify.
2. After solidification, apply each type of sunscreen in a two inch circle in the middle of three of the petri dishes with seperate cotton swabs and leave the last one blank.
3. Lay all four petri dishes under an ultraviolet lamp, and turn the lamp on and leave it on for twenty- four hours.
4. After turning the lamp of, put the dishes in a dark place, and leave them there for twenty- four hours.
5. After twenty- four hours, observe the changes and record the color changes on each of the petri dishes.

I tried this 4 times and the results are inconclusive. Nothing has happened to any of the petri dishes. Do you have any suggestions for me?

[kgudger]

Hello and Welcomje to the Forums!

This sounds like an interesting experiment, but I'm not sure what you're looking for? Do you have a hypothesis? Is there a similar experiment on the internet somewhere I could look at to see what you're doing? Thanks!

Keith