lenses preap physics. critical angle at a certain angle where no ray will emerge into the less dense...
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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 reflectionPhenomenon 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 n1 sin q1 = n2 sin q2
= n2 sin 90
sin q1 = n2 / n1
Fiber Optics
A.K.A. Optical fibers or light pipesThin 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 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.
NearsightednessYour 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
FarsightednessEye 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:
1 1 1
d d fo i
Mh
h
d
di
o
i
o
The ratio M is called the magnification, ho is the object’s size and hi is the image size.
Where do is the object’s distance, di is the image distance and f is the focal length.
R radius of curvature
+ converging
- diverging
f focal length
+ converging
- diverging
doobject distance
+ real object
+ real object
diimage distance
+ real images
- virtual images
hoobject size
+ if upright
- if inverted
hiimage 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.
do = 30 cm
f = 10 cm
dd f
d fio
o
30 10
30 10
( )= 15 cm, real
b. What is the height of the image?
ho = 5 cm h
h
d
di
o
i
o
hd h
dii o
o
15 5
30
( )= - 2.5 cm, inverted