UV Beads
Students learn about experimental design using plain white beads that turn different colors when placed in UV light.

Concepts
Observations, ultraviolet radiation, visible light

Materials
6 UV detecting beads
Stopwatch
White index card
Different light sources
? – Other materials may be necessary depending on the experiments students have designed

Getting Started
In this activity some equipment can be laid out for the students in advance but they should not be told how it is to be used. The goal of this activity is for students to decide how they will test for UV radiation by themselves, to perform the test and then modify their experiment to make it better.

Student Instructions
From start to finish conduct an experiment that tests which types of light sources emit ultraviolet (UV) light. Below is a UV level indicator (picture) and an outline to help you perform the experiment from start to finish.

uv level purple beads.jpg
Quantitative way to measure the amount of UV exposure to the UV beads.



Define the Problem
Which light sources emit ultraviolet radiation?

Make Observations
Make observations of the different light sources you will be testing (but don’t expose the UV beads to them yet!).


Research the Topic
Research ultraviolet light and visible light. What are they? Additionally, research sources of ultraviolet light.


Form a Hypothesis
Which light sources do you believe will contain some UV light?



Design an Experiment
Materials


Method



Conduct the Experiment
Record your data and repeat the experiment to obtain better data.


Draw Conclusions
Was your hypothesis confirmed? Explain why or why not?


Re-design the Experiment
How well did the experiment go? Take this opportunity to review the experiment you conducted and see if there is a better way to perform it. Talk about your experiment and the results with peers and see what input they have in making it better. After re-designing the experiment, conduct the experiment again.


Draw Conclusions Again
Did the experiment work better the second time? Explain the results of the second experiment and compare them to the first.



Explanation
The electromagnetic spectrum is composed of many different frequencies of energies which include radio waves, visible light, ultraviolet light and x-rays. The only part of the electromagnetic spectrum we can see is visible light; all other parts of the spectrum are invisible to us, and this includes ultraviolet light. UV-sensitive beads contain a pigment that changes color when exposed to ultraviolet light from the sun or certain other types of light sources. Common sources of light such as incandescent bulbs and fluorescent bulbs do not emit a significant amount of UV light.

For the UV beads to react the wavelength of the UV light needs to be between 300 – 360 nanometers (nm). That range includes high energy UV Type A (320 – 400 nm) and low energy UV Type B (280 – 320 nm). Besides the sun, a good source of UV light is a long fluorescent black light. Although they look like they should work, incandescent black lights will not change the color of the beads.

figure11.jpg
Figure 11: The top UV beads have been exposed to ultraviolet light while the bottom ones have not.

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