Light & Optical Systems Reflection & Refraction. Notes

Transcription

1 Light & Optical Systems Reflection & Refraction Notes

2 What is light? Light is electromagnetic radiation Ultra-violet + visible + infra-red

3 Behavior of Light Light behaves in 2 ways particles (photons) Ray-like behavior bounce, reflect waves Radiate outwards, bend Wave-particle duality

4 Optical Systems? Comprise optical components and devices that use or control light Examples Assistance for eyesight (microscopes) Motion control Elevator light beam detects presence of person in doorway Cameras Communications Fiber optics

5 Laser Light? Light Amplification by Stimulated Emission of Radiation Characteristics Pure color Travels in a single direction Waves are in phase (coherent) Uses are many Surgery, measurement, welding, sighting weapons

6 Ray Optics: Reflection Light rays travel in straight lines Shadows Reflection Light ray bounces off the surface of a material according to the Law of Reflection The angle of incidence = angle of reflection

7 Reflection Amount of reflection off a surface depends on the nature of the surface Shiny vs dull Mirrors Plane Concave (converging) Convex (diverging)

8 Reflection Concave mirrors Mirror axis Vertex Focus (focal length Center of curvature (radius)

9 Reflection Convex mirrors Mirror axis Vertex Focus (focal length Center of curvature (radius) All images are behind the mirror = virtual!

10 Characteristics Focus (or focal point) (F) Through which the reflected rays pass Focal length (f) Distance from center of mirror to focus Optical (mirror) axis Axis perpendicular to mirror at its center (vertex) Center of curvature (C) Center of the spherical mirror Radius of curvature (R) 2 x focal length

11 Ray Tracing Concave mirror Draw 2 rays from the object to the mirror Through focal point to mirror and back Parallel to mirror then through focal point At the intersection, the image is formed

12 Ray Tracing Convex mirror Draw 2 rays from the object to the mirror To center of curvature through mirror and back Parallel to mirror then through focal point At the intersection, the (virtual) image is formed

13 Ray Optics: Refraction

14 Speed of light Light rays travel at a speed of 3 x 10 8 m/s in a vacuum, but slow down when passing through other material Ex. In water light travels at ~ 2.25 x 10 8 m/s Different colors of visible light travel at slightly different speeds when refracted Rainbow from prism

15 What is refraction? Refraction is the bending of light that takes place at a boundary between 2 materials having different indices of refraction, or Refraction occurs due to a change in the speed of light as it passes from one medium to another, according to relative indices of refraction

16 What is Index of Refraction (n)? Ratio of the speed of light in a vacuum (3 x 10 8 m/s) to the speed of light in the material of interest Ex. What is the index of refraction of water? n = light speed in a vacuum light speed in water n = 3 x x 10 8 n = 1.33

17 Common Indices of Refraction Material N Ice 1.31 Water 1.33 Crown glass 1.52 diamond 2.42

18 Basic Rules for Refraction Whenever light passes into a material with a higher index of refraction, the light is bent toward the normal Whenever light passes into a material with a lower index of refraction, the light is bent away from the normal

19 Snell s Law n i * sin (i) = n r * sin (R)

20 Lenses and Refraction Used to change the direction of light rays by bending Uses Telescopes, eyeglasses, cameras 2 basic types Convex lens used to focus light rays Concave lens used to spread light rays

21 Convex (Converging) Lens Thicker at the center than the edges 2 focal points Parallel light rays focus to a point (F ) on the other side of the lens Light rays emanating from a focal point (F) pass through the lens and exit as parallel rays 1 focal length f = f

22 Concave (Diverging) Lens Thicker at the edges than the center 2 focal points Parallel light rays spread out after passing through the lens (focal point F ) Converging rays, heading toward focal point F of the lens, are refracted and emerge as parallel rays 1 focal length f = f

23 Diameter of lens The larger the diameter of the lens, the more light is allowed to pass through Like the pupil in our eyes, In low light the pupil is wide open In bright light, the pupil is reduced

24 Ray tracing with lenses A parallel ray passes through the lens and through the focal point A ray passes directly through the center of the lens A ray passes through the incident focal point and is refracted parallel to the principal axis Intersection of these 3 rays identifies the image