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Natural Science - Year I

Unit 20: The Optics of Lenses

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Science Weblecture for Unit 20


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Science Lecture for Unit 20: Optics

For Class
Outline/Summary

Studying Light Phenomena

Our work this week focusses on the phenomena of light. What do we mean by color? Intensity? How does light behave when it bounces off a surface? When it is transmitted through materials like air and glass?

    Use the Patterns of Light modules on Light and Optics to learn about light, reflection, refraction, and color.
    • What is the difference between refraction and reflection?
    • Which object refracts--a lens or a mirror? Which reflects?
    • What is meant by the focal length of the lens? How can it be measured?
    • What happens light passes through an interface between different media, such as glass and air?
    • What happens to the speed of light when it goes from air into glass?
    • What is the refractive index of a medium?
    • A transparent blob of goo has a large refractive index (3). What does this imply about the speed of light in the goo?
    • What is the difference between a real image and a virtual image.
    • What is the difference between a concave and a convex lens? How does each refract light?
    • Lens A has a negative focal length: where is its focal point?
    • Lens B has a positive focal length: where is its focal point?
    • Which mirrors can create a real image, a convex mirror or a concave mirror? Why? (Look at both sides of a large spoon and see!)
    • Why do you only need 2-3 "rays" to show how the light going through a lens will bend?

    Things to learn from rainbows (Optics in Nature)

    • Which color reflects more, red, blue, or green?
    • How does the air act like a lens?
    • How does a raindrop disperse and reflect light, acting like both a prism and a mirror?
    • What is the antisolar point? Why do we want to know where it is in order to look for a rainbow?
    • Do you see the same rainbow as your friend who is a few feet away from you?
    • Why do secondary rainbows occur?

Study/Discussion Questions:

Further Study/On Your Own