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Reversible Focusing of Light Beam with Easy Tracing Lines

Explore the reversibility of focusing a parallel beam of light and locate images formed by lenses using easy-to-trace lines. Discover the relationship between magnification and focal length, object distance, and image distance.

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Reversible Focusing of Light Beam with Easy Tracing Lines

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  1. The focusing of a parallel beam of light to a focus is reversible:

  2. 3 easy to trace lines can help locate the image formed by a lens p f f q q M= p With the magnification,

  3. 1 2 3 f f/2 4 5 The ray entering this diverging lens, parallel to its axis, exits the other side following which ray?

  4. The divergence by a concave lens should be reversible as well!

  5. 1 2 3 f f/2 4 Which ray entering the diverging lens exits the other side parallel to its axis? 5

  6. 3 easy to trace lines can help locate the image formed by a lens p f q f q M= p With the magnification still,

  7. 1 p 1 q 1 f = + When viewing objects by eye, which variable(s) of the lens equation must always remain fixed? • the focal length, f • the object distance, p • the image distance, q (4)both f and p (5)both f and q (6)both p and q

  8. For everyone there is a NEAR POINT, the closest position you can focus on f Any closer, the lens cannot accommodate. The eye strains to hold f this small.

  9. 1 p 1 q 1 f = + ho q p The retinal image size must be proportional to • the focal length, f of the lens • the object distance, p • the image distance, q (4)the object size, ho (5)both p and q (6)both p and ho

  10. ho  q 

  11. A jeweler whose near point is 40 cm, examines a diamond with a small magnifying glass. The lens has a focal length of 5 cm and the image is -185 cm from the lens. • Determine the angular magnification. • Where should the image be located for • viewing without eyestrain? • What is the magnification then? • c)What maximum magnification is possible?

  12. A jeweler whose near point is 40 cm, examines a diamond with a small magnifying glass. The lens has a focal length of 5 cm and the image is -185 cm from the lens. • Determine the angular magnification. • b)Where should the image be located for • viewing without eyestrain? • What is the magnification then? • c)What maximum magnification is possible? Want q=- , so 1/q = 0  When q=-N 

  13. Some answers: 2 Directed away from the focus on far side. 2 Directed toward the focus on near side. (3) the image distance, q

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