Lenses

Carol Bible                    Carter Elementary
                               5740 S. Michigan
                               Chicago IL 60637
                               (312) 535-0860

Objectives:

Students in grades 5-8 will discover, through exploration and observation, what 
lenses are and what lenses can do.

Materials Needed:

concave lenses                  solid glass or plastic cylinder
convex lenses                   paper
Florence glass                  black marker
plain glass                     overhead projector with arm lowered
Fresnel lens                    light box with an arrow on a screen
baggie filled with water        lens holders   
spray bottle with water         index card with "AMMONIUM DIOXIDE" written
meter sticks                    large lens with long focal length
baggies

Strategy: 

Opening activities

1.  Hand out baggies filled with a convex lens, a concave lens and a plain piece 
of glass.  Students explore and discuss what they observe about these objects. 

2.  Set up the overhead projector removing or lowering the arm.  Explain that 
the overhead projector has a lens with a light below it.  Turn off the lights 
and spray a steady stream of water over and above the lens.  Students will 
observe that a sort of funnel can be seen with a narrowing in the middle.  The 
point at which the spray of water narrows represents the focal point (the point 
at which the light rays converge). 
 
3.  Hold a piece of blank paper over the lens and find the focal point.  
Children will be able to observe that the light will be smallest and most 
intense at that point.  Then take a black marker and darken the center of the 
paper.  Hold the paper over the lens again at the focal point.  Students will 
observe the paper begin to smoke. 

4.  Show students the light box with the arrow on it.  Observe the direction of 
the arrow.  Turn off the lights and project the image of the arrow on the wall.
Students will observe that the image is upside down. 

Stations-Students will be divided into cooperative groups of four.  Each group 
will receive an activity sheet with activities to be performed and questions to 
be answered at each station. 

Station #1 - Display convex lenses with various focal lengths.  Students will 
focus the overhead light onto a paper and notice the distance between the lens 
and the brightest image (this is called the focal length).  They will do this 
for all of the lenses, make observations about the focal length of these lenses 
and record any other observations. 

Station #2 - Students will find an object in the room and describe the image 
that they see when they look at it through a Florence glass and then a baggie 
filled with water.  Students will determine whether the Florence glass and the 
baggie are examples of lenses. 

Station #3 - Attach two convex lenses, one with a relatively short focal length 
and the other a long focal length, to a meter stick using lens holders. Students 
will look through one lens and then both lenses.  Then they will focus on an 
object far away by moving the lenses back and forth on the meter stick.  
Students will determine what happens to the image and what this device could be 
used for.  (Telescope) 

Station #4 - Attach two convex lenses, both with short focal lengths of about 5 
cm., to a meter stick using the lens holders.  Students will move the lenses 
back and forth and focus on a written page from a newspaper or the like.  
Students will determine what happens to the image and what this device could be 
used for.  (Microscope) 

Station #5 - Display the Fresnel lens.  Students will determine if it is a lens 
and if so, how it is the same or different from the other lenses. 

Station #6 - Mystery Lab!  Students will explain what is happening when they 
look at the words AMMONIUM DIOXIDE through a solid glass cylinder. 

Performance Assessment:

Activity sheets from each group will be collected and assessed.