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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

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