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Learn about concave and convex lenses, refraction, terminology, and ray diagrams for clear understanding of lens behavior. Complete homework assignments based on ray diagrams.
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Chapter 13: Lenses and Optical Devices 13.1 Lenses and the Formation of Images
Basic Lens Shapes There are two basic shapes of lenses: • ConcaveLenses (Diverging) • ConvexLenses (Converging)
Converging Lens • Parallel light rays converge through a single point after they travel through the lens. • Lens is thickest in the middle • Diverging Lens • Parallel light rays diverge after they travel through the lens. • Lens is thickest at the edge
Lenses use Refraction • Light is refracted twice as it passes through a lens: once from air to glass, and once from glass to air. • Ray diagrams are simplified by drawing a dashed line through the center of the lens and showing refraction occurring at this line.
terminology • Axis of Symmetry: imaginary vertical line drawn through the optical centre perpendicular to the principal axis (through the middle of the lens) • Optical centre: point where the axis of symmetry meets the principal axis • Principal focus: where all the rays meet. • Secondary principal focus: point on the other side of the lens equal in distance from the principal focus.
Diverging (Concave) Lenses Light rays of a diverging lens do not converge. If you project these diverging rays backwards, it looks as if they come from a virtual focus.
Uses of Concave Lenses • Images formed are smaller, virtual and upright. • Some types of eyeglasses and telescopes use concave lenses along with convex lenses (which are more useful)
Ray Diagrams with Converging Lenses Table 11.7 on p. 453 • 1)Copy this table into your notebook (includes uses) • 2)Copy the steps for drawing a convex lens ray diagram on page 454 in your notebook.
Homework / Classwork P. 454 #1-4