Curved Mirrors

Participants developed their own Learning Cycles, set up labs, and reported their findings to the group.

I. Assessing Prior Knowledge:
Many teachers asked questions about curved mirrors in everyday life or had examples of mirrors. Some asked students to find examples of curved mirrors before starting the lesson.

II. Exploring:
Many teachers had the students look at concave and convex mirrors and the kinds of images formed. They did this before any quantitative lab. Middle school teachers said that they would stop after the qualitative.

High school teachers would have students take measurements and data about images similarly to what they had done with lenses. Some would ask the students to design the lab themselves.

Graphs would be done similarly to those for lenses.

III. Explanations:
Teachers found that concave mirrors acted like convex lenses.

• Both were converging, that is, they focused parallel rays from distant objects.
  
• Both made enlarged, virtual, right-side-up images when the object was closer than the focal point. They were magnifying lenses or glasses.
  
• Both made inverted, real images when the object was farther than the focal point.

Teachers found that convex mirrors acted like concave lenses.

• Both caused parallel rays to diverge (spread out).
  
• Both made reduced, virtual, right-side-up images, no matter how far or close the object was. These are used for door peep holes or wide angle lenses or mirrors.

Teachers found that the same equations worked for mirrors as for lenses. See equations.

Ray diagrams were similar to those for lenses, except the rays reflected off the mirror, instead of going throught the lenses. See:

• Beginning ray diagrams.
  
• Diverging mirror and rays.
  
• Concave and convex mirrors and rays. Choose "mirror" in the pop-up box.

IV. Applications

• Explain everyday mirrors and their uses.
  
• Do Brain Teasers #21-26.

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  - Index for Optics.
  - All S.F. Bay Area PTRA Workshops.

  Andria Erzberger
  2/1/01