TITLE:  Concave and Convex Mirrors and Lenses
Presented to grade level 5

GOALS
Concave and Convex Mirrors and Lenses is designed to teach fifth grade level students about light relection and refraction as shown in curved mirrors and lenses.
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SPECIFIC OBJECTIVES

• Light rays are reflected off of opaque surfaces and if these surfaces are very shiny as mirrors are, they will produce an image.
• A concave mirror bends in towards the center like the inside of a bowl and a convex mirror bends outward to the edges.
• Light rays are reflected inwards toward a focal point by concave mirrors.  A concave mirror can produce images that are right side up and very large or upside down.
• Light rays are reflected outwards by a convex mirror.  Images produced by a convex mirror will always appear right side up and smaller than the actual object.
• Light rays are refracted as they pass through translucent objects such as lenses.
• A concave lens is thicker at the edges than it is at the center, and a convex lens is thicker in the middle than it is at its edges.
• A concave lens refracts light rays spreading them outward producing an image that is upright and smaller than the actual object.
• A convex lens refracts light rays inward.  If a convex lens is held close to a person’s eyes, they will see an image that is upright and larger than the actual object.  If the convex lens is held further away from a person’s eyes, they will see an image upside down.
• A refracting telescope uses two convex lenses to magnify images in the sky.  A reflecting telescope uses a concave mirror, a plane mirror, and a convex lens to do the same job.
• A microscope, like a reflecting telescope, uses a concave mirror, a plane mirror, and a convex lens.  However, they are used to magnify very small images on slides not in the sky.

BACKGROUND
        Concave mirrors bend inward like a cave.  These mirrors reflect light rays inward towards a focal point.  Images will appear upside down from far away, but very close to the mirror, they will appear right side up and very large.  In contrast, concave lenses reflect light rays outwards.  The image through a concave lens will always be right side up.
        Convex mirrors curve outwards and reflect light rays away from the center.  Images will appear right side up and smaller than the actual object.  Convex lenses, on the other hand,  refract light rays in toward a central point.  The image seen through a convex lens is upside down when the lens is held away from your face, but the image is magnified and right side up when the lens is held closer to your eye.
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SOLs COVERED

SOL 5.9

The students will describe the effects of lenses and mirrors on the path of light.  Descriptive statement: Experiences should include the manipulation of lenses and mirrors and examples of their uses in flashlights, eyeglasses, cameras, and telescopes.

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DEMONSTRATIONS AND EXHIBITS
Materials needed:  tennis ball, cereal bowl, shiny spoon, concave-lensed eyeglasses, magnifying glass, two convex lenses, plane mirror, concave mirror, microscope; also possible access to a reflecting telescope.

1. Light rays are reflected from mirrors.
Concave mirrors:

• With a tennis ball and a cereal bowl, show how light rays will reflect back to a central point.  It is helpful to draw the reflected rays on an overhead.
• Using a concave mirror, show students how they will appear upside down from far away and right side up very close to the mirror.  You can use a shiny spoon as a replacement for a mirror.

• With a cereal bowl and a tennis bowl, bounce the tennis ball off of the back side of the bowl to show how light rays will reflect outwards off of a convex mirror.  It is helpful to draw the rays reflecting on an overhead.
• Using the back side of a spoon, show students that their image will always be right side up and smaller than normal.  Compare this image with the front of the spoon.

• Using concave-lensed eyeglasses allow students to look through the lens to observe the upright image.  Draw parallels to the convex mirror which reflects light rays away from the center.
• Use an image to show how concave lenses cure nearsightedness when an eyeball is too long.

• Use a magnifying glass to demonstrate how images can be either right side up or upside down.  Draw parallels to the concave mirror which reflects rays toward a central point.
• Make an overhead to explain how convex lenses can be used to correct farsightedness when an eyeball is too short.

• A reflecting telescope uses two convex lenses.  Use two successive convex lenses to show the students how they can magnify an image.  If you have access to a reflecting telescope, allowing them to look through one would be helpful.
• A refracting telescope uses a concave mirror, a plane mirror, and a convex lens to magnify images.  Have the students try to arrange these three components to magnify an image.
• A microscope uses the same arrangement of lenses and mirrors to magnify slides.  Show students a cell under a microscope. (See interactive exercise.)

INTERACTIVE EXERCISES
Materials needed:  microscope, clean microscope slide and cover, sample specimen (onion layer, a typed letter, eyelash, etc.)

1. Prepare a slide for the microscope.

• Let the students see the item without magnification, and prepare a dry or wet mount (as appropriate for the sample).  They can then observe the specimen under the microscope and compare the images.  Is it inverted?  Why or why not?

INTERESTING EXAMPLES
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OTHER RESOURCES
 

Literature	Pasachoff, Jay M.  2000. Science Explorer:  Sound and Light. Prentice Hall, Upper Saddle River, NJ. Walpole, Brenda.  1988. 175 Science Experiments to Amuse and Amaze Your Friends.  Random House, New York, NY.
Local Places to Visit	University of Virginia observatories
Related Web Sites

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