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LENSES

LENSES. Lyzinski Physics. Light Speeds. When traveling through a vacuum, light travels at 3 x 10 8 m/s. This is the fastest light ever travels. We shall refer to this as the SPEED OF LIGHT. When traveling through a different “medium” (substance), light slows down .

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LENSES

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  1. LENSES Lyzinski Physics

  2. Light Speeds • When traveling through a vacuum, light travels at 3 x 108 m/s. This is the fastest light ever travels. We shall refer to this as the SPEED OF LIGHT. • When traveling through a different “medium” (substance), light slows down. • The INDEX OF REFRACTION compares this slower speed to the speed of light in a vacuum. Speed of light Speed of light in new medium Index of refraction

  3. The Index of Refraction • What does “refract” mean. It means “to bend”. When light travels from one medium to another it actually bends (thus causing it to either slow down or speed up) • The index of refraction is always GREATER THAN 1 (because the speed in a medium is always less than the speed of light). • Optically “DENSE” mediums have a higher index. We will call these mediums “HEAVY” • Optically “LESS DENSE” mediums will be called “LITE”(mis-spelled )

  4. Some common mediums More Dense

  5. Refraction (the bending of light) Normal to the surface Normal to the surface Crown glass n =1.52 air n =1.00 water water n =1.33 n =1.33 If light travels from HEAVY into LITE, it bends AWAY FROM the normal If light goes from LITE to HEAVY, it bends TOWARD the normal. “La-Hite” (LHT) “Ha-La” (HLA)

  6. “Ha-La” has a “Phenomena” associated with it. Total Internal Reflection Normal heavy lite

  7. Normal to the surface air n =1.00 water n =1.33 SNELL’S LAW How much does the light bend??? Relates the angles to the indexes

  8. Light bends away from the normal in the “lite” air air glass air Light bends towards normal in the “heavy” glass Prisms cause light to bend LHT HLA IMPORTANT QUESTION: Does all light bend the same amount?

  9. All light does NOT bend the same amount in a prism. Why does the index increase going from R to I (in ROY-G-BIV)? Increasing index (bend) Decreasing wavelength

  10. wavelength frequency Wave speed The Wave Equation The frequency of light never changes once it is created. Velocity can change. Wavelength will then also change. But frequency never changes once the wave is generated. If v goes , then l must go . If v goes , n goes .

  11. Normal to the surface L H Refraction (the bending of light) Normal to the surface H L If light travels from HEAVY into LITE, it speeds up AND the wavelength increases If light goes from LITE to HEAVY, it slows down AND the wavelength decreases.

  12. Primary Focus Principal axis Concave Lenses Concave lenses are similar to stacking two prisms.

  13. Primary Focus Principal axis Convex Lenses Convex lenses are also similar to stacking two prisms.

  14. Any ray parallel to the principal axis is reflected through the focus. How do you locate the image formed in a LENSE Situation. 2. Any ray through the focus is reflected parallel to the principal axis. 3. Any ray through the center of the lens passes directly through the lense following its same path.

  15. Same Size, Inverted, Real NO IMAGE!!! VIRTUAL!!! Smaller, Inverted, Real LARGER, Inverted, Real Image Formation in CONVERGING Lenses F 2F 2F’ F’ Inside F’ Between 2F’ & F’ Outside 2F’ On F’ On 2F’

  16. Image Formation in Diverging Lenses F’ F All images are VIRTUAL and smaller than the object

  17. BOTH use converging lenses with the object far beyond the secondary focus. Cameras …… Film ….. and the human eye

  18. Magnifying Glasses F 2F 2F’ F’ Larger, virtual image that you see Object that you are looking at (under the lens)

  19. Film Projectors White screen

  20. Human eye Virtual Image that your eye sees Lens #2 (Eyepiece) Microscopes Lens #1 (Objective)

  21. Muscles that “tense” the lens Cornea: Protective “Window” of eye Iris: Colored part that acts like a camera shutter. Pupil: Hole in the middle of the iris. Lens: has adjustable focal length. Retina: Where image is formed. Optic nerve: Sends image to brain where it is flipped upside down. The Human Eye

  22. Far Point Near-Sightedness Diverging Lens creates a virtual image of the “far away” object that is inside (or at) the far point. The eye sees this virtual image clearly. Object beyond the far point can’t be focused clearly on the retina  “Fuzzy” vision Furthest Point that the eye can see clearly

  23. Near Point Focus of lens Converging Lens creates a virtual image of the “too close” object that is outside (or at) the near point. The eye sees this virtual image clearly. Far-Sightedness Object inside the near point can’t be focused clearly on the retina  “Fuzzy” vision Closest Point that the eye can see clearly

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