# Change in UV Radiation

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#### Updated on Feb 04, 2012

Grade Level: 6th - 8th; Type: Physical Science

This project monitors the strength of solar UV radiation during the day.

The goal of the experiment is to have the student test a hypothesis about the way UV radiation varies throughout the day by collecting data, and then use that data to revise the initial hypothesis (if necessary).

• Does the UV Index vary from day to day?
• Does it vary with temperature?
• Does it vary with the presence or absence of cloud cover?
• Does it vary with the presence or absence of atmospheric haze?

The amount of ultraviolet radiation that reaches the earth’s surface on any given day is typically highest around noon. This is because the sun’s rays travel the shortest distance to the earth’s atmosphere at that time. But other factors such as amount of cloud cover, and the presence of atmospheric haze can also affect how much UV reaches the earth’s surface.

• UV detector, calibrated to the National Weather Service’s UV Index (\$30)
• Materials can be found on the internet (amazon.com).
1. Based on your experience with getting sunburned at night, formulate a hypothesis to explain how selected factors affect the amount of ultraviolet radiation that reaches the earth varies during the day.
2. Using a handheld UV detector, measure the UV Index – the strength of the solar UV radiation on a scale of 1 (low) to 11 (extremely high), at one hour intervals from sunrise to sunset.
3. Record the date, the temperature and whether there is any cloud cover or haze each time you make a UV Index measurement. Also record the status or value of any other factor that you have chosen to track.
4. Perform the same measurements each day for one month.
5. Plot the UV Index as a function of temperature, day of the month, whether there was cloud cover, and whether there was any haze present. Note any trends.
6. Compare the results of the experiment with your initial hypothesis. If necessary revise it and make new measurements to test the revision.