What would the control variable be in an experiment like this?

[deleted-314315]

If you were to measure the intensity of UV rays according to the UV index using a UV monitor, and your goal was to determine what time of the day the rays were most intense, what would the control variable be?

I assumed the independent(manipulated) variable would be the time of the day you are measuring the rays, and the dependent(responding) variable would be the measurement you would get, but I don't see a clear controlled(constant) variable would be.

I was thinking perhaps the increments in which you measured the rays?

For example if you measured them every hour and kept that consistent?

[deleted-295056]

I know this can get somewhat confusing but I will try to answer your question. A control is generally different from a variable in an experiment. We include controls that are of a known value in our experiments. If we are testing a new tooth filling material we run the same experiment with at least one material that we have used for years. We know the values that we should be getting for that material. That allows us to know whether the experiment was run correctly. If the value of the known control is the same as the experimenter got in his testing then we know that his testing was done correctly. You might not have a control for this experiment

If you would like to have a control in your experiment, I would suggest finding a large light like a streetlight that you could put your UV tester under each night, or before and after your experiment. You could measure the amount of UV you are receiving from that light and use it as a control to make sure that the UV detector is reading well and has not changed values during your experiment. We always measure either the light that we are using or the light detector before and after any experiment. That tells us that the detector was working correctly during the experiment.

Time is indeed a controllable variable for this experiment. The time of the most UV radiation should be when the Sun is directly over you in the sky so you would not have to measure this all day long. You might wish to measure every half hour or even quarter hour during times when the Sun is over head. Your shadow would also help you in determining the time when the sun is overhead as it will get very short when the Sun is directly above you. Remember when you are standing out in the Sun that you should wear some sort of sunscreen or hat.

You are going to have at least one uncontrollable variable that you might not have considered in this experiment depending on how long you will run the experiment. You will have the time of year as a factor. In Summer and Winter the angle of the sun if different and the time of the most UV radiation would vary somewhat.

Weather will also be a consideration. Rain will block some to all of the UV radiation that you receive on any given day. Whether it is cloudy or sunny will effect the values that you get, but will still show you the time of the most UV radiation.

I am not saying any of this to discourage you, but to help you with the experiment. We do the same thing before performing any experiment. We try to figure out all of the things that can vary in the experiment and think of ways to keep them from changing the values we receive. One thing that you could do in your experiment would be to not take measurements on any rainy or very cloudy days in your experiment.

I hope all of this answered your question. If I made it too confusing, please tell me and I will try to answer the question better. Please let me know how the experiment came out.