GEOMETRIC OPTICS

TWO KIND OF REFLECTIONS

The reflection of light can be roughly categorized into two types of reflection: specular reflection is defined as light reflected from a smooth surface at a definite angle, and diffuse reflection, which is produced by rough surfaces that tend to reflect light in all directions

TWO KIND OF REFLECTIONS

Specular reflection Diffuse reflection

When the diffuse reflection occur?

It is hard to belive, but you have to know that all objects reflect rays, but those which surface is not flat give diffuse reflection and become indirect-lighting device. Yes, your hand also reflects and diffuse much of the light it receives. Its surface is rough, so rays have different angles of incidence and different angles of reflection and are diffused. This phenomenon allows us to see objects which are not the sources of light.

FLAT MIRROR

A virtual image is produced by a flat mirror because of specular reflection How the mirror build a virtual image?

How the mirror work?

The incident and reflected rays all lie in a plane that includes the normal (dashed line).

How the mirror work?

h h’

Images are classified as real or virtual. A real image is formed when light rays pass through and diverge from the image point; a virtual image is formed when the light rays do not pass through the image point but appear to diverge from that point.

Lateral magnification

How the mirror work?

A flat mirror produces an image that has an apparent left–right reversal.

You can see this reversal by standing in front of a mirror and raising your

right hand. The image you see raises its left hand. Likewise, your hair appears to be parted on the side

opposite your real part, and a mole on your right cheek appears to be on your

left cheek.

Quick Quiz!!

In the overhead view, the image of the stone seen by observer 1 is at C. Where does observer 2 see the image—at A, at B, at C, at D, at E, or not at all?

The Fermat Principle

The time required for light to travel from point A to B is the minimum time required For propagation in the same medium, the velocity is a constant and this minimizing the time is the same as minimizing the distance traveled.

The Fermat Principle

Three possible paths from A to B are shown. Let's look at the arbitrary path ACB. If point A' is constructed on the perpendicular AO such that AO = A'O, the right triangles AOC and A'OC are equal. Thus AC = A'C and the distance traveled by the ray of light from A to B via C is the same distance from A' to B via C. The shortest distance from A' to B is obviously the straight line A'DB, so the path ADB is the correct choice taken by the actual light ray.

Spherical Mirror

A spherical mirror, as its name implies, has the shape of a section of a sphere. This type of mirror focuses incoming parallel rays to a point, as demonstrated bythe colored light rays.

Concave Mirror

The incoming rays from the object are essentially parallel because the source is assumed to be very far from the mirror. We call the image point in this special case the focal point F and the image distance the focal length f = R/2

Concave Mirror

(a) A concave mirror of radius R. The center of curvature C is located on theprincipal axis. (b) A point object placed at O in front of a concave spherical mirror of radius R, where O is any point on the principal axis farther than R from the mirror surface, forms a real image at I. If the rays diverge from O at small angles, they all re.ect through the same image point.

Concave Mirror

Concave Mirror

Lateral magnification :

Mirror equation : In term of f :

Concave Mirror

When the object is located so that the center of curvature lies betweenthe object and a concave mirror surface, the image is real, inverted, and reduced in size.

Concave Mirror

When the object is located between the focal point and a concave mirror surface, the image is virtual, upright, and enlarged.

Convex Mirror

When the object is in front of a convex mirror, the image isvirtual, upright, and reduced in size.

How to describe an image ?

fqp

111

10

11

25

1

qcmq 7.16

The magnification is given by

Assume that a certain spherical mirror has a focal length of +10.0 cm. Locate and describe the image for object distances of (a) 25.0 cm, (b) 10.0 cm, and (c) 5.00 cm.

We find the image distance by using mirror equation:

668.025

7.16

p

qM

The image is real, inverted, and reduced in size.

Because q is positive, the image is real

Because of 0.668 less than 1, the image is reduce in size

Because M is negative, the image is inverted

Look at the figure

Index of Refraction

The index of refraction (n) is defined as the speed of light (c) in

vacuum divided by the speed of light in the medium (vp).

Speed of light, c = 3.108 m/s

c = 300000 km/s

Index of Refraction

What is the speed of light inside water?

What is the speed of light inside a diamond?

Material Index, n

Vacuum 1.00000

Air 1.0008

Water 1.330

Glass 1.510

Diamond 2.417

Ruby 1.760

Ice 1.30

Snell’s Law Snell's Law relates the indices of refraction n of the two media to the

directions of propagation in terms of the angles to the normal.

Refraction

Some Efects of Refraction

Critical Angle

When light passes through a medium of high refractive index into a medium of lower refractive index, the incident angle of the light waves becomes an important factor. If the incident angle increases past a specific value, it will reach a point where the angle is so large that no light is refracted into the medium of lower refractive index. The four yellow light rays all have an angle of incidence (i) low enough to pass through the interface between the two media. However, the two red light rays have incident angles that exceed the critical angle (approximately 41 degrees) and are reflected either into the boundary between the media or back into the high refractive index medium.

Critical Angle / Total Reflection

The following picture shows the total reflection of light inside the glass block. The light enters the glass block from the lower right and travels in a zigzag way inside the glass block by total reflection. 

Optical fiber / Total reflection

Convex Lens and Concave Lens

OPTICAL DEVICES

Eye

Eye Structure

Eye

Incident Light enter to eye

Eye

Miopi PresbiopiCataract

Eye

Optical Prism

Lup

Lup Magnification

Lup

Angular Magnification

Akomodasi Minimum Akomodasi Maksimum

The Camera Priciple

The Camera Priciple

The Camera Focus

Inside a Camera

Microscope

Microscope

Microscope

Microscope

M = | s' ok / s ok | | s' ob / s ob |

d = s ok + s' ob (Jarak kedua lensa)

Mo [ pp / fe ]

Mo [ pp / fe + 1 ] + 1

Akomodasi Minimum

Akomodasi Maksimum

Linear Magnification

Angular Magnification

MA = 1 / M

Telescope

Reflector Telescope Refractor Telescope

Telescope

Reflector Telescope Refractor Telescope

Telescope