Discovering UV                     Presenter: Andy Jackson, Harrisonburg City Schools, ajackson@harrisonburg.k12.va.us.        

                       

Va. SOL:

PH.10  The student will investigate and understand that different frequencies and wavelengths in the electromagnetic spectrum are phenomena ranging from radio waves through visible light to gamma radiation. Key concepts include

a)     the properties and behaviors of radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays; and

b)    current applications based on the wave properties of each band.

 

National Standards:

 

Electromagnetic waves result when a charged object is accelerated or decelerated. Electromagnetic waves include radio waves (the longest wavelength), microwaves, infrared radiation (radiant heat), visible light, ultraviolet radiation, x-rays, and gamma rays. The energy of electromagnetic waves is carried in packets whose magnitude is inversely proportional to the wavelength.

 

Topic/Concept

Students will be introduced to the visible spectrum and through the demonstration be allowed to discover the presence of Ultraviolet.

 

Materials

Š      1 glow in the dark strip

Š      1 overhead projector

Š      1 diffraction grating for projector

Š      two pieces of posterboard or file folder

 

Safety Considerations

 

None

 

Presentation

 

The glow in the dark strip is taped to a section of whiteboard to be mounted in front of projector. It is sealed from light with a covering for several hours before the demonstration. The students are introduced to the glow in the dark material by showing a small sample in the lit room and then turning off the lights. Students are shown the visible spectrum on the front board. The glow in the dark strip is positioned in front of the visible spectrum (still sealed against light). Students are asked to predict what will happen to the glow in the dark strip if the room is darkened and the strip is illuminated with the spectrum. Use markers or chalk to indicate student predictions.  A common prediction is for the part of the strip that is illuminated by green will glow. Carefully mark the different pieces of the visible spectrum. Darken the room except for the projected spectrum and remove the glow in the dark strips covering.  Turn off the projector and mark the portion of the strip that glows. Discuss results.

 

 

 

 

 


How the physics is demonstrated

 

In this demonstration the glow in the dark strip will glow from the blue on up past the last of the visible violet portion of the spectrum.  Allow students to discover the presence of UV in the spectrum coming from the overhead. This also can be a staring point for discussing the idea of activation energy and that there is more energy in the blue end of the spectrum. Even after the strip is glowing you can use a red laser show that red will not make it glow.

 

 

Construction  and Tips Regarding the Demonstration

You need about 1 meter of glow in the dark material and small section for demonstrating the material before the experiment. I fasten the 1 meter strip to a section of whiteboard and cover it up with a piece of Styrofoam insulation taped over it. I prop this set up on my whiteboard’s marker tray and project the spectrum on top of it.

 

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Sources & References

Glow in the dark vinyl strip and sheet of diffraction grating were purchased from Educational Innovations www.teachersource.com .