Spec Lab 2    Visible and Invisible Light

Your Task
             Explore your own eye's response to the spectrum from white light, and compare with the ALTA's sensor.  Show that the ALTA can 'see' light that your eyes cannot, and that you can see that the ALTA cannot.

Materials
 

A rainbow  (from a prism) a small ruler 1 ALTA Spectrometer

Glow-in-the-dark plastic Lesson 2 Data Sheet 1 Lesson 2 Data Sheet 2

Procedure
1.   Go to the backboard where the prisms are prepared for you.   Turn on the lamp.

2.  Look carefully at the rainbow, and notice the different colors you see.  Are they all there?

3.  Place a sheet of white paper on the board so the rainbow lies in the middle of it.   Place a small ruler next to the rainbow and draw a straight line beside it.   Make a scale on the line, following the centimeter marks on the ruler.

4.  On the scale line,  record the boundary between each color (between red and orange, orange and yellow, etc).  Discuss with your partner about where the boundaries are.  Do both of you see it exactly the same?  Try to agree on the boundaries.

5.  Record the boundary distances on Data Sheet 1.
 

6.  You can see the purple (violet) light.  What light is 'beyond' the purple light ?     _______________________

7.  You can see the red wavelength light.  What light is 'beyond' the red light ?     _______________________

You eyes cannot see the wavelengths in questions 6 and 7.  We will use the Spectrometer to detect the invisible light.

8.  Use the ALTA Spectrometer.  You will NOT push any buttons for this experiment.  Just use the detector and read the display.
First take a background light reading.   Point the Spectrometer at a place on the white board but not on the rainbow.  Record the display on Data Sheet 2.   This gives you a reading for the level of background light in the room.

9.  Take several measurements at various distance across the rainbow of colors.  Do not put the Spectrometer flat on the blackboard.  Hold it so the rainbow light is still visible.  Be careful about what the detector is pointing to..... look behind the Spectrometer to see where it is pointing.  Take measurements on both sides of the rainbow too.... try to measure the invisible kinds of light too!  (try to get 6-10 readings).   Record the scale distance and the display number for each color on Data Sheet 2.  

10.   Which wavelengths of light (visible or invisible colors) cause
          a.  the strongest response on the ALTA spectrometer?      ________________________
          b.  That means the ALTA is very sensitive to  _________________________

          c.  the weakest response on the ALTA spectrometer?   ____________________
          d. That means the ALTA is not sensitive to ____________________________
 

11.  Complete Data Sheet 2 by doing the calculations for the 4th column.  Subtract the Background number from the Display number for each color you observed.
 

12.  Try this (it may not work!)   Put some glow-in-the-dark plastic in each color of the rainbow, including the areas on both side.  Do you notice any interesting responses?  (Pay attention especially to the purple area and beyond.)
 

Summarize your results
 What did you learn about  your own eye's response to the spectrum from white light?   Compare with the ALTA's sensor.  Can the  ALTA  'see' light that your eyes cannot?   Can you see that the ALTA cannot?