Lenses PreAP Physics

Critical Angle At a certain angle where no ray will emerge into the less dense medium. –For water it is 48  which does not allow the ray to enter the air Light ray is only reflected inside the more dense medium. –Other Examples Glass (43  ) Mirrors (90-95  ) Diamonds (24.6  )

Total internal reflection Phenomenon that involves the reflection of all the incident light off the boundary. Only takes place when both of the following two conditions are met: – –Light is in the more dense medium and approaching the less dense medium. – –Angle of incidence is greater than the so-called critical angle.

Critical Angle n 1 sin   = n 2 sin   = n 2 sin 90 sin   = n 2 / n 1

Fiber Optics A.K.A. Optical fibers or light pipes Thin glass fibers –Use Total Internal Reflection Developed for communication and data transmission –Replacing electric circuits and microwave links Thousands of miles of it in our phone lines

Fiber Optics

Other examples of Total Internal ReflectionTotal Internal Reflection

THIN LENSES Lenses are an essential part of telescopes, eyeglasses, cameras, microscopes and other optical instruments. A lens is usually made of glass, or transparent plastic.

A converging (convex) lens is thick in the center and thin at the edges. A diverging (concave) lens is thin in the center and thick at the edges.

Nearsightedness Your eye focuses images in front of the retina –Objects far away appear fuzzy, but objects up close can be seen To correct Place a concave lens to refocus the light so it focuses on the retina

Farsightedness Eye focuses the light behind the retina. –Objects close up are fuzzy and objects far away are clearer. To correct –Place a convex lens to refocus the light so it focuses on the retina

IMAGE FORMATION BY LENSES There are three principal rays to locate an image.

Principal Rays Review Ray Diagram for both types of lenses.

2 Types of Images for Lenses A real image is always formed on the side of the lens opposite to the object. A virtual image will appear to be on the same side of the lens as the object.

26.3 a.Find the images formed by the following lenses using the Ray Tracing method. b. Write the characteristics of each image: -real or virtual, -larger, smaller or same size as object and -upright or erect.

Convex Lens with Object Beyond 2F

Convex Lens with Object at 2F

Convex Lens with Object Inside Focal Point

Convex Lens with Object Between 2F and F

No image is formed. Convex Lens with Object at Focal Point

Concave Lens with Object Beyond 2F

Concave Lens with Object Inside Focal Point

THE LENS EQUATION The lens equation can be used to locate the image: The ratio M is called the magnification, h o is the object’s size and h i is the image size. Where d o is the object’s distance, d i is the image distance and f is the focal length.

R radius of curvature + converging- diverging f focal length + converging- diverging dodo object distance + real object didi image distance + real images - virtual images hoho object size+ if upright- if inverted hihi image size+ if upright- if inverted

26.4 A 5 cm tall object is located 30 cm from a convex lens of 10 cm focal length. a. Find the location and nature of the image. d o = 30 cm f = 10 cm = 15 cm, real b. What is the height of the image? h o = 5 cm = cm, inverted