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Lenses
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2. Activity: Ray Boxes and Lenses
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3. 5.3 Using Lenses to Form Images
A lens is a curved piece of transparent material that can bend (refract) light rays in useful ways to help form a well-focused image.
A lens can be concave or convex.
See page 190
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4. Review
Recall when light passes from air to a denser material like glass, it bends toward the normal.
When it passes out of the glass, it bends away from the normal.
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5. Concave Lenses thinner in the middle than at the edge.
cause light rays to diverge (spread out) and never meet.
No focal point.
Curve inward
See page 191
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6. Concave Lenses Image is always upright and smaller than the object.
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7. Concave Lenses - Uses
Sometimes used in eyeglasses (for nearsightedness, contact lenses, flashlights, peepholes, binoculars, telescopes,  and in photography.
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8. Convex Lenses thicker in the middle.
light rays to converge (come together) at a focal point.
See page 192
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9. Convex Lenses
Light passing through the thicker, more curved areas will bend more than light passing through flatter areas.
A light ray passing straight through the center is not refracted
See page 192
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10. Image depends on distance
Image depends on how far object is from focal point.
Focal length is the distance from the centre of the lens to the focal point.
See page 193
Take the Section 5.3 Quiz
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11. Focal Length
When object is more than two focal lengths away from the lens, its image is reduced (smaller) and upside down
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12. Convex Lens and Focal Length
When object is between one and two focal lengths from the lens, its image is enlarged and upside down.
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13. Convex Lens and Focal Length
When object is at one focal length from the lens, there is no image because rays never meet.
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14. Convex Lens and Focal Length
When object is less than one focal length from the lens, its image is enlarged and upright.
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16. Convex Lens Microscopes, magnifying glass Camera lens
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17. Homework Read pages 190-193 Answer CYU p197 #1-7 Lens WS
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18. Focal length in Convex Lenses
If an object is between the lens and the focal point (less than on focal length), the image is upright and larger than the object.
If an object is more than one focal length away form the lens, the image is upside down and smaller than the object.
See page 193
Take the Section 5.3 Quiz
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