Hi rohankohli0820,
I agree that your result is counterintuitive. Kudos to you for trying to figure out why your results turned out the way that they did!
You're doing this project, correct?
https://www.sciencebuddies.org/science- ... p058.shtml
One possibility is that some of the compounds that initially dissolved into the water are breaking down when the tea has for 300 seconds. If the breakdown products don't absorb as much light, then perhaps the resistance would drop because more light would reach the bottom of the cup. I'm not familiar enough with the detailed chemistry of tea making to know how plausible this explanation might be.
Alternatively, something about your measurement setup may have changed in some way. I'n inclined to think that this is the more likely scenario. Perhaps the light in the room was slightly brighter when you measured the 300 second cup? Or the aluminum foil shifted slightly, which let in light from the side?
If your science fair project is due soon, then one way of dealing with this would be to say in your results/conclusion section that the 300 second brew result seemed unusual based on your other results. If you have more time between now and when your project is due, you could also re-run the experiment and see if you get the same results.
It's quite common for professional scientists to re-run an experiment if the result is unexpected. If the result is still unexpected, then the scientist would dig deeper to find out why. But, if the result of the re-run experiment is in line with what the scientist expected, then the scientist would conclude that the first experiment was somehow flawed.
Post back as you have other questions.