189
OPTICS: BASICS CONCEPTS Md Anisur Rahman (Anjum) Professor & Head of the department (Ophthalmology) Dhaka Medical College, Dhaka

Dr Md Anisur Rahman Optics basics concepts

Embed Size (px)

Citation preview

Page 1: Dr Md Anisur Rahman Optics basics concepts

OPTICS: BASICS CONCEPTS

Md Anisur Rahman (Anjum)Professor & Head of the

department (Ophthalmology)Dhaka Medical College, Dhaka

Page 2: Dr Md Anisur Rahman Optics basics concepts

What is optical science.

Optical science. Though most people associate the word

‘optics’ with the engineering of lenses for eyeglasses,

telescopes, and microscopes,

In physics the term more broadly refers to the study of

the behavior of light and its interactions with matter.

Page 3: Dr Md Anisur Rahman Optics basics concepts

Three broad subfields of optics

1) Geometrical optics, the study of light as rays

2) Physical optics, the study of light as waves

3) Quantum optics, the study of light as particles

Page 4: Dr Md Anisur Rahman Optics basics concepts

Geometrical optics

Light is postulated to travel along rays – line

segments which are straight in free space but may

change direction, or even curve, when encountering

matter.

Page 5: Dr Md Anisur Rahman Optics basics concepts

Geometrical optics

Two laws dictate what happens when light encounters

a material surface. The law of reflection, evidently

first stated by Euclid around 300 BC, states that when

light encounters a flat reflecting surface the angle of

incidence of a ray is equal to the angle of reflection.

Page 6: Dr Md Anisur Rahman Optics basics concepts

1. Geometrical optics

• The law of refraction, experimentally determined by

Willebrord Snell in 1621, explains the manner in

which a light ray changes direction when it passes

across a planar boundary from one material to

another.

Page 7: Dr Md Anisur Rahman Optics basics concepts

From the laws of reflection and refraction:

One can determine the behavior of optical devices

such as telescopes and microscopes.

One can trace the paths of different rays (known as

‘ray tracing’) through the optical system

Page 8: Dr Md Anisur Rahman Optics basics concepts

How images can be formed?

Their relative orientation, and their magnification.

This is in fact the most important use of geometrical

optics to this day: the behavior of complicated optical

systems can, to a first approximation, be determined

by studying the paths of all rays through the system.

Page 9: Dr Md Anisur Rahman Optics basics concepts
Page 10: Dr Md Anisur Rahman Optics basics concepts

2. Physical optics

Looking again at the ray picture of focusing above, we

run into a problem: at the focal point, the rays all

intersect. The density of rays at this point is therefore

infinite, which according to geometrical optics

implies an infinitely bright focal spot. Obviously, this

cannot be true.

Page 11: Dr Md Anisur Rahman Optics basics concepts

• If we put a black screen in the plane of the focal point

and look closely at the structure of the focal spot

projected on the plane, experimentally we would see

an image as simulated below:

Page 12: Dr Md Anisur Rahman Optics basics concepts
Page 13: Dr Md Anisur Rahman Optics basics concepts

• There is a very small central bright spot, but also

much fainter (augmented in this image) rings

surrounding the central spot. These rings cannot be

explained by the use of geometrical optics alone, and

result from the wave nature of light.

Page 14: Dr Md Anisur Rahman Optics basics concepts

• Physical optics is the study of the wave properties of

light, which may be roughly grouped into three

categories:

1) Interference,

2) Diffraction, and

3) Polarization. 

Page 15: Dr Md Anisur Rahman Optics basics concepts

 Interference

 Interference is the ability of a wave to interfere with

itself, creating localized regions where the field is

alternately extremely bright and extremely dark.

Page 16: Dr Md Anisur Rahman Optics basics concepts

Diffraction

Diffraction is the ability of waves to ‘bend’ around

corners and spread after passing through an aperture. 

Page 17: Dr Md Anisur Rahman Optics basics concepts

Polarization 

Polarization refers to properties of light related to its

transverse nature. We will cover all these terms in

more detail in subsequent posts.

Page 18: Dr Md Anisur Rahman Optics basics concepts

Quantum optics

We return to the picture of the focal spot illustrated

above and now imagine that the light source which

produces the focal spot is on a very precise dimmer

switch. What happens as we slowly turn the dimmer

switch down to the off position?

Page 19: Dr Md Anisur Rahman Optics basics concepts

• Physical optics predicts that the shape of the focal

spot will remain unchanged; it will just grow less

bright. When the dimmer switch is turned below some

critical threshold, however, something different and

rather unexpected happens: we detect light in little

localized ‘squirts’ of energy, and do not see our ring

pattern at all.

Page 20: Dr Md Anisur Rahman Optics basics concepts

If we keep a running tally of how many squirts hit at each location, we can slowly build up an average picture of where light energy is being

deposited in above figure.

Page 21: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 21

Geometric Optics

Geometric Optics deals with the formation of images by using

such optical devices as lenses, prisms and mirrors and with the

laws governing the characteristics of these images, such as their

size, shape, position and clarity.

Rays of light

Pencil of light

Beam of light

• (M.A MATIN P=19)

Page 22: Dr Md Anisur Rahman Optics basics concepts

Reflection

The law of reflection, evidently first stated by Euclid

around 300 BC, states that when light encounters a

flat reflecting surface the angle of incidence of a ray

is equal to the angle of reflection

Page 23: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 23

Reflection of light

• When light meets an interface between two media, its

behavior depends on the nature of the two media

involved. Light may be absorbed by the new medium

or transmitted onward through it or it may bounch

back into first medium. This bouncing of light at an

interface is called Reflection.

(M.A MATIN = 21)

Page 24: Dr Md Anisur Rahman Optics basics concepts

Q. What happened to the light when it strikes a surface?

Ans) 3 things may happen. It may be:

Absorbed

Reflected

Or Refracted

Page 25: Dr Md Anisur Rahman Optics basics concepts

Defination of Reflection

Reflection is defined as the change of path of light

without any change in the medium.

All the reflections end up in producing images of the

object kept in front of the reflecting surface.

Page 26: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 26

Laws of Reflection

1) The incidence ray and the reflected ray lie in the same plane which is perpendicular to the mirror surface at the point of incidence.

2) When light is reflected off any surface, the angle of incidence is always equal to the angle of reflection,

Page 27: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 27

Mirror

• A mirror is optical media which reflects light

backwards when fall on it. It may be:

1) Plane mirrors or

2) Spherical mirrors.

Page 28: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 28

Mirror: Rules for rays tracing through a mirror

1) The ray which pass through the pole shall pass undeviated.

2) The ray which is parallel with the axis shall pass through the focal point after convergence or divergence.

3) The ray passing through the focal point & falling on the mirror surface shall pass parallel to the optical axis.

4) The ray passing through the centre of curvature of a mirror shall also pass undeviated.

5) Path of light rays are also reversible.

Page 29: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 29

Reflection at a plane surface

Page 30: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 30

Spherical Mirrors

• Silvering a piece of glass which would form part of

the shell of a hollow sphere. Silvering the glass on

the outside gives a concave or converging mirror,

while silvering on the inside gives a convex or

diverging mirror.

Page 31: Dr Md Anisur Rahman Optics basics concepts
Page 32: Dr Md Anisur Rahman Optics basics concepts

Types of images

There are two types of images formed mirrors. They

are:

• 1) Virtual image.

• 2) Real image.

Page 33: Dr Md Anisur Rahman Optics basics concepts

Virtual image

1) Virtual image can not be focused on a screen.

2) It is always upright.

3) No light is really passing through the apparent

location of the image.

4) The virtual image formed by plane mirror is laterally

inverted

Page 34: Dr Md Anisur Rahman Optics basics concepts

Real image

1) Real image can be focus on a screen.

2) It is always inverted.

3) The light passes through the location of the image.

Page 35: Dr Md Anisur Rahman Optics basics concepts

Nomenclature

1) Light rays falling on the surface are called incident

rays.

2) Light rays travelling back are called reflected rays.

3) A line at right angle to the reflecting surface is called

normal

4) Light travelling along the normal is reflected back

along the normal

Page 36: Dr Md Anisur Rahman Optics basics concepts

angle of incident.

angle of reflection.

Page 37: Dr Md Anisur Rahman Optics basics concepts

Nomenclature

5) The angle formed by the incident ray and the normal

is called angle of incident.

6) The angle formed by the reflected ray and the normal

is called angle of reflection.

7) The angle of incident and the angle of reflection are

equal.

Page 38: Dr Md Anisur Rahman Optics basics concepts

Nomenclature

8) The incident ray, the reflected ray and the normal are

in the same plane.

9) The line joining the centre of curvature to any point

on the curved mirror is the normal of that mirror.

10) The focal length of the plane mirror is infinity.

Page 39: Dr Md Anisur Rahman Optics basics concepts

Image formation by plain mirror

If the reflecting surface of the mirror is flat then we

call this type of mirror as plane mirrors. Light always

has regular reflection on plane mirrors.

Given picture below shows how we can find the

image of a point in plane mirrors.

Page 40: Dr Md Anisur Rahman Optics basics concepts
Page 41: Dr Md Anisur Rahman Optics basics concepts

Characteristics of image formed by a plane mirror.

1) Image is virtual and erect.

2) It is of same size as the object.

3) It has the same distance as object to the mirror.

4) It is laterally reversed.

5) The minimum length of the mirror required to form full

size image of the object is half the size of the object.

Page 42: Dr Md Anisur Rahman Optics basics concepts

Number of images

How many images can you form by two plane

mirror?

It depends upon the inclination of two mirrors with

each other.

• The number of images formed by two plane mirrors

inclined to each other is calculated by the formula:

Page 43: Dr Md Anisur Rahman Optics basics concepts

Number of images

• N=360/ ᴓ - 1 (Here, N = number of images form, ᴓ is

the angle between two mirrors)

• Less the angle between two mirrors, more the number

of images.

Page 44: Dr Md Anisur Rahman Optics basics concepts

Number of images

N = 360/90 – 1 = 4 – 1 = 3.

N = 360/60 – 1 = 6 – 1 = 5

N= 360/45 – 1 = 8 – 1 = 7.

An object placed between two parallel plane mirrors will

form infinite number of images.

This is true only for mirrors kept at right angles or less

than that.

Page 45: Dr Md Anisur Rahman Optics basics concepts

Uses of plane mirror in ophthalmology

1) A plane mirror is used at a distance of 3 m with a

reverse Snellen’s chart kept at little higher position

than patient’s head.

2) Used in plane mirror retinoscope.

3) Used in both direct & indirect ophthalmoscope.

4) Used in slit lamp, synaptophore, stereoscope, to

change the direction of rays & save space.

Page 46: Dr Md Anisur Rahman Optics basics concepts

Spherical mirror

Pole Center of curvature

Page 47: Dr Md Anisur Rahman Optics basics concepts

Nomenclature in spherical mirror image

1) Pole: It is the vertex of the mirror.

2) Center of curvature: It is the center of curvature of the

sphere out of which the mirror is fashioned.

3) Radius of curvature: It is the line joining the center of

curvature to the pole.

4) Principal axis: It is the ling joining center of curvature

and the vertex.

Page 48: Dr Md Anisur Rahman Optics basics concepts

Nomenclature in spherical mirror image

5) Normal in a spherical mirror: It is a line that joins

any point of the mirror to the center of curvature.

6) All the measurements are valid from the pole of the

center.

7) By convention, all the incident rays are taken to

travel from the left to right.

Page 49: Dr Md Anisur Rahman Optics basics concepts

Nomenclature in spherical mirror image

• 8) Focal length of a concave mirror is taken as

negative and positive in convex lens

Page 50: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 50

The principal axis of a spherical mirror is the line joining the pole P or centre of the mirror to the centre of curvature C which is the centre of the sphere of which the mirror forms a part.

P C

Page 51: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 51

radius of curvature r

• The radius of curvature r is the distance CP. In the

case of a concave mirror the centre of curvature is in

front of the mirror ; in a convex mirror it is behind.

Page 52: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 52

Principal Focus

• When a parallel beam of light falls on a plane mirror it is

reflected as a parallel beam ; but in the case of a concave

mirror the rays in a parallel beam are all reflected so as to

converge to a point called a focus.

• If the incident rays are parallel to the principal axis the point

through which all the reflected rays pass is on the principal axis

just midway between the pole and the centre of curvature and

is called the principal focus F.

Page 53: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 53

• What happens when a beam of light parallel to the

principal axis falls on a convex mirror?

• In this case the rays are reflected so that they all

appear to be coming from a principal focus midway

between the pole and centre of curvature behind the

mirror.

Page 54: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 54

• A concave mirror, therefore has a real principal focus,

while the convex mirror has a virtual one.

• The focal length of a spherical mirror is half its radius

of curvature.

Page 55: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 55

Construction of ray diagrams

• Since a point on an image can be located by the point of

intersection of two reflected rays, we have to consider which

are the most convenient rays to use for this purpose.

• Remembering that, by geometry, the normal to a curved

surface at any point is the radius of curvature at that point, one

very useful ray to draw will be one which is incident along a

radius of curvature. Since this is incident normally on the

mirror, it will be reflected back along its own path.

Page 56: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 56

Construction of ray diagrams

• Another useful ray is one which falls on the mirror parallel to

the principal axis. By definition, this will be reflected through

the principal focus. Conversely, any incident ray passing

through the principal focus will be reflected back parallel to

the principal axis. The same observations also apply to the

convex mirrors, so we may briefly sum them up into a set of

rules for constructing images formed by spherical mirrors.

Page 57: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 57

Construction of ray diagrams

1) Rays passing through the centre of curvature are reflected back

along their own paths.

2) Rays parallel to the principal axis are reflected through the

principal focus.

3) Rays through the principal focus are reflected parallel to the

principal axis.

4) (Useful when using squared paper) Rays incident at the pole

are reflected, making the same angle with the principal axis.

Page 58: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 58

Images formed by a concave mirror

• . We wish to describe the characteristics of the image for any given object location. The L of L•O•S•T represents the relative location. The O of L•O•S•T represents the orientation (either upright or inverted). The S of L•O•S•T represents the relative size (either magnified, reduced or the same size as the object). And the T of L•O•S•T represents the type of image (either real or virtual). The best means of summarizing this relationship between object location and image characteristics is to divide the possible object locations into five general areas or points:

Page 59: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 59

Images formed by a concave mirror

Case 1: the object is located beyond the center of curvature (C)

Case 2: the object is located at the center of curvature (C)

Case 3: the object is located between the center of curvature

(C) and the focal point (F)

Case 4: the object is located at the focal point (F)

Case 5: the object is located in front of the focal point (F)

Page 60: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 60

Page 61: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 61

Case 1: The object is located beyond C

When the object is located at a location beyond the

center of curvature, the image will always be located

somewhere in between the center of curvature and the

focal point.

• In this case, the image will be an inverted image.

reduced in size;

Page 62: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 62

The object is located beyond C (contd)

• Finally, the image is a real image. Light rays actually

converge at the image location. If a sheet of paper

were placed at the image location, the actual replica

of the object would appear projected upon the sheet

of paper.

Page 63: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 63

Case 1: The object is located beyond C

Page 64: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 64

Case 2: The object is located at C

When the object is located at the center of curvature,

the image will also be located at the center of

curvature.

In this case, the image will be inverted. The image

dimensions are equal to the object dimensions.

Finally, the image is a real image.

Page 65: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 65

Case 2: The object is located at CLight rays actually converge at the image

location. As such, the image of the object could be projected upon a sheet of paper.

Page 66: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 66

Case 3: The object is located between C and F

When the object is located in front of the center of

curvature, the image will be located beyond the

center of curvature.

In this case, the image will be inverted.

The image dimensions are larger than the object

dimensions.

Page 67: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 67

Case 3: The object is located between C and FFinally, the image is a real image. Light rays

actually converge at the image location. As such, the image of the object could be projected upon a sheet

of paper.

Page 68: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 68

Case 4: The object is located at F

• When the object is located at the focal point, no

image is formed. Light rays from the same point on

the object will reflect off the mirror and neither

converge nor diverge. After reflecting, the light rays

are traveling parallel to each other and do not result in

the formation of an image.

Page 69: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 69

Case 4: The object is located at F

Page 70: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 70

Case 5: The object is located in front of F

When the object is located at a location beyond the focal point,

the image will always be located somewhere on the opposite

side of the mirror. Regardless of exactly where in front of F

the object is located, the image will always be located behind

the mirror.

In this case, the image will be an upright image, magnified and

virtual

Page 71: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 71

Case 5: The object is located in front of F

Page 72: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 72

Case 5: The object is located in front of F

• This type of image is formed by a shaving or make-up mirror

and also by small concave mirror used by dentists for

examining teeth.

Page 73: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 73

Case 5: The object is located in front of F

Light rays from the same point on the object reflect off the mirror

and diverge upon reflection. For this reason, the image

location can only be found by extending the reflected rays

backwards beyond the mirror. The point of their intersection is

the virtual image location. It would appear to any observer as

though light from the object were diverging from this location.

Any attempt to project such an image upon a sheet of paper

would fail since light does not actually pass through the image

location.

Page 74: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 74

• It might be noted from the above descriptions that there is a

relationship between the object distance and object size and

the image distance and image size. Starting from a large value,

as the object distance decreases (i.e., the object is moved

closer to the mirror), the image distance increases; meanwhile,

the image height increases.

Page 75: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 75

• At the center of curvature, the object distance equals the

image distance and the object height equals the image height.

• As the object distance approaches one focal length, the image

distance and image height approaches infinity.

• Finally, when the object distance is equal to exactly one focal

length, there is no image.

Page 76: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 76

• Then altering the object distance to values less than one focal

length produces images that are upright, virtual and located on

the opposite side of the mirror.

• Finally, if the object distance approaches 0, the image distance

approaches 0 and the image height ultimately becomes equal

to the object height.

Page 77: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 77

• Nine different object locations are drawn and labeled with a

number; the corresponding image locations are drawn in blue

and labeled with the identical number.

Page 78: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 78

Page 79: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 79

IMAGE FORM BY CONVEX MIRROR

Page 80: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 80

IMAGE FORM BY CONVEX MIRROR

Page 81: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 81

IMAGE FORM BY CONVEX MIRROR

The diagrams above show that in each case, the image is

located behind the convex mirrora virtual imagean upright imagereduced in size (i.e., smaller than the object)

Page 82: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 82

IMAGE FORM BY CONVEX MIRROR

Unlike concave mirrors, convex mirrors always produce images that share these characteristics. The location of the object does not affect the characteristics of the image. As such, the characteristics of the images formed by convex mirrors are easily predictable.

Page 83: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 83

IMAGE FORM BY CONVEX MIRROR

• Another characteristic of the images of objects formed by convex mirrors pertains to how a variation in object distance affects the image distance and size. The diagram below shows seven different object locations (drawn and labeled in red) and their corresponding image locations (drawn and labeled in blue).

Page 84: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 84

IMAGE FORM BY CONVEX MIRROR

Page 85: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 85

IMAGE FORM BY CONVEX MIRROR

• The diagram shows that as the object distance is decreased, the image distance is decreased and the image size is increased. So as an object approaches the mirror, its virtual image on the opposite side of the mirror approaches the mirror as well; and at the same time, the image is becoming larger.

Page 86: Dr Md Anisur Rahman Optics basics concepts

Image formed by concave mirror

Position of the object

Position of the image

Nature of the image

Inverted/ Erect

Size

Between focus & pole

Behind the mirror

Virtual Erect Magnified

At focus Infinity Real Inverted Highly Magnified

Between focus & curvature

Beyond center of curvature

Real Inverted Little Magnified

Page 87: Dr Md Anisur Rahman Optics basics concepts

Image formed by concave mirror

Position of the object

Position of the image

Nature of the image

Inverted/ Erect

Size

Center of curvature Same place Real Inverted

Same size

Beyond the center of curvature

Between focus & center of curvature

Real Inverted

Diminished

At infinity Real Inverted

Very small

Page 88: Dr Md Anisur Rahman Optics basics concepts

Image formed by convex mirror

The image of an object kept in front of the mirror is

formed behind the mirror.

It is smaller than the object , erect and virtual.

The distance between the image and the mirror is less

than between the object and the mirror.

Page 89: Dr Md Anisur Rahman Optics basics concepts

Behavior of images in relation to position of the object

The image formed by CONVEX and PLANE mirrors are virtual

The image formed by CONCAVE mirrors can be real or virtual

The distance between mirror and the image is least in CONVEX mirror, most in CONCAVE mirror and

equal in PLANE mirror

Page 90: Dr Md Anisur Rahman Optics basics concepts

specular reflection & diffuse reflection

Reflection of smooth surfaces such as mirrors or a

calm body of water leads to a type of reflection

known as specular reflection.

Reflection of rough surfaces such as clothing, paper,

and the asphalt roadway leads to a type of reflection

known as diffuse reflection.

Page 91: Dr Md Anisur Rahman Optics basics concepts

• Whether the surface is microscopically rough or

smooth has a tremendous impact upon the subsequent

reflection of a beam of light.

Page 92: Dr Md Anisur Rahman Optics basics concepts

specular reflection & diffuse reflection

The diagram depicts two beams of light incident upon a rough and a smooth surface.

Page 93: Dr Md Anisur Rahman Optics basics concepts

Applications of Specular and Diffuse Reflection

There are several interesting applications of this

distinction between specular and diffuse reflection.

One application pertains to the relative difficulty of

night driving on a wet asphalt roadway compared to a

dry asphalt roadway. Most drivers are aware of the

fact that driving at night on a wet roadway results in

an annoying glare from oncoming headlights.

Page 94: Dr Md Anisur Rahman Optics basics concepts

Applications of Specular and Diffuse Reflection

The glare is the result of the specular reflection of the

beam of light from an oncoming car. Normally a

roadway would cause diffuse reflection due to its

rough surface. But if the surface is wet, water can fill

in the crevices and smooth out the surface.

Page 95: Dr Md Anisur Rahman Optics basics concepts

Applications of Specular and Diffuse Reflection

• Rays of light from the beam of an oncoming car hit

this smooth surface, undergo specular reflection and

remain concentrated in a beam. The driver perceives

an annoying glare caused by this concentrated beam

of reflected light.

Page 96: Dr Md Anisur Rahman Optics basics concepts

Applications of Specular and Diffuse Reflection

A second application of the distinction between

diffuse and specular reflection pertains to the field of

photography. Many people have witnessed in person

or have seen a photograph of a beautiful nature scene

captured by a photographer who set up the shot with a

calm body of water in the foreground.

Page 97: Dr Md Anisur Rahman Optics basics concepts

Applications of Specular and Diffuse Reflection

The water (if calm) provides for the specular

reflection of light from the subject of the photograph.

Page 98: Dr Md Anisur Rahman Optics basics concepts

Applications of Specular and Diffuse Reflection

Light from the subject can reach the camera lens

directly or it can take a longer path in which it

reflects off the water before traveling to the lens.

• Since the light reflecting off the water undergoes

specular reflection, the incident rays remain

concentrated (instead of diffusing).

Page 99: Dr Md Anisur Rahman Optics basics concepts

Applications of Specular and Diffuse Reflection

The light is thus able to travel together to the lens of the camera and produce an image (an exact replica) of the subject which is strong enough to perceive in the photograph. An example of such a photograph is shown.

Page 100: Dr Md Anisur Rahman Optics basics concepts

Question

If a bundle of parallel incident rays undergoing

diffuse reflection follow the law of reflection, then

why do they scatter in many different directions after

reflecting off a surface?

Page 101: Dr Md Anisur Rahman Optics basics concepts

Answer

Each individual ray strikes a surface which has a

different orientation. Since the normal is different for

each ray of light, the direction of the reflected ray

will also be different.

Page 102: Dr Md Anisur Rahman Optics basics concepts

Question

Perhaps you have observed magazines which have

glossy pages. The usual microscopically rough

surface of paper has been filled in with a glossy

substance to give the pages of the magazine a smooth

surface. Do you suppose that it would be easier to

read from rough pages or glossy pages? Explain your

answer.

Page 103: Dr Md Anisur Rahman Optics basics concepts

It is much easier to read from rough pages which provide

for diffuse reflection. Glossy pages result in specular

reflection and cause a glare. The reader typically sees an

image of the light bulb which illuminates the page. If

you think about, most magazines which use glossy pages

are usually the type which people spend more time

viewing pictures than they do reading articles.

Page 104: Dr Md Anisur Rahman Optics basics concepts

Refraction

Page 105: Dr Md Anisur Rahman Optics basics concepts

Luminous versus Illuminated Objects

The objects that we see can be placed into one of two

categories: luminous objects and illuminated objects.

Luminous objects are objects that generate their own

light

Illuminated objects are objects that are capable of

reflecting light to our eyes.

Page 106: Dr Md Anisur Rahman Optics basics concepts

The sun is an example of a luminous object, while the

moon is an illuminated object.

Page 107: Dr Md Anisur Rahman Optics basics concepts

Refraction

Q) What happened to the light when it strikes a surface?

Ans) 3 things may happen. It may be:

Absorbed

Reflected

Or Refracted

Page 108: Dr Md Anisur Rahman Optics basics concepts

Refraction

Q) What is refraction?

Ans) Refraction of light is a phenomenon of change in

the path of light when it passes from one medium to

another due to change in velocity.

Page 109: Dr Md Anisur Rahman Optics basics concepts

Terms used in refraction

1) NORMAL: This is a line right angles to the interface

2) INCIDENCE RAY: The ray that strikes the interface

at the base of the normal in an angular fashion.

3) REFRACTED RAY: This is the deviated ray in the

second medium.

Page 110: Dr Md Anisur Rahman Optics basics concepts

4) ANGLE OF INCIDENCE: Angle between the

normal and the incident ray

5) ANGLE OF REFRACTION: The angle between the

refracted ray & the normal is called ANGLE OF

REFRACTION

6) The two angles are never equal.

Page 111: Dr Md Anisur Rahman Optics basics concepts

Snell’s Law

Page 112: Dr Md Anisur Rahman Optics basics concepts

Total Internal Reflection (TIR)

Page 113: Dr Md Anisur Rahman Optics basics concepts

Critical Angle

Critical angle is the angle of incidence above which total internal reflection occurs.

It is defined as the angle when the incidence ray is of such an angle that the refracted ray is at right angles to the normal

Page 114: Dr Md Anisur Rahman Optics basics concepts

Critical Angle

• Critical angle of glass is 48.60, diamond is 240 (refractive

index is 2.42) and water is 48.750. An incident ray when

passing through a slab of glass with air on either side will exit

the slab as refracted ray and will be parallel to incident ray.

Page 115: Dr Md Anisur Rahman Optics basics concepts

Total Internal Reflection (TIR)

• The complete reflection of a light ray reaching an

interface with a less dense medium when the angle of

incidence exceeds the critical angle.

Page 116: Dr Md Anisur Rahman Optics basics concepts

Total Internal Reflection (TIR)

Page 117: Dr Md Anisur Rahman Optics basics concepts

Different uses of TIR

1) Gonioscopy employs total internal reflection to view

the anatomical angle formed between the

eye's cornea and iris.

2) Total internal reflection is the operating principle

of optical fibers, which are used in endoscopes and

telecommunications.

Page 118: Dr Md Anisur Rahman Optics basics concepts

Different uses of TIR

3) Total internal reflection is the operating principle of

automotive  rain sensors, which control automatic  

windscreen/windshield wipers

Page 119: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 119

Lenses

Page 120: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 120

Lenses

A lens is defined as a portion of a refracting medium

bordered by two curved surfaces which have a

common axis.

When each surface forms part of a sphere the lens is

called a spherical lens.

Page 121: Dr Md Anisur Rahman Optics basics concepts

Sometimes, a spherical lens has a one plane surface, it

is acceptable because a plane surface can be thought

of as part of a sphere of infinite radius.

Page 122: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 122

Spherical Lens

Lens may be spherical (when each surface forms part

of sphere, the lens is called a Spherical lens) where

the concavity or convexity two different meridians

are equal.

Page 123: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 123

Cylindrical Lens

It may be cylindrical where there is unequal

concavity in two meridians. The two meridians

usually remains at right angels to each other and the

less curved meridian being designed as axis of the

lens.

Page 124: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 124

Lenses: (A–F), Spherical lenses: (A), biconvex; (B), biconcave; (C), planoconvex; (D), planoconcave; (E), concavoconvex, periscopic convex, converging meniscus; (F), convexoconcave, periscopic concave, diverging meniscus; (G, H), cylindrical lenses, concave and convex.

Page 125: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 125

Page 126: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 126

Spherical Aberration

The prismatic effect of the peripheral parts of the

spherical lens causes spherical aberration.

It was seen that the prismatic effect of a spherical lens

is least in the paraxial zone and increases towards the

periphery of the lens.

Page 127: Dr Md Anisur Rahman Optics basics concepts

Spherical Aberration

Thus, rays passing through the periphery of the lens

are deviated more than those passing through the

paraxial zone of the lens.

Page 128: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 128

Correction of Spherical Aberration

Spherical aberration may be reduced by occluding the

periphery of the lens by the use of “stops” so that

only the paraxial zone is used.

Lens form may also be adjusted to reduced spherical

aberration, e,g plano-convex is better than biconvex.

To achieve the best results, spherical surface must be

Page 129: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 129

Correction of Spherical Aberration

abandoned and the lenses ground with aplantic surface,

that the peripheral curvature is less than the central

curvature.

Another technique of reducing spherical aberration is

to employ a doublet. This consists of a principal lens

and a somewhat weaker lens of different R.I

cemented together.

Page 130: Dr Md Anisur Rahman Optics basics concepts

Correction of Spherical Aberration

The weaker lens must be of opposite power, and

because it too has spherical aberration, it will reduce

the power of the periphery of the principal lens more

than the central zone. Usually, such doublets are

designed to be both aspheric and achromatic.

Page 131: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 131

• A convex lens is thicker at the centre than at the edges.

Page 132: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 132

Image form by lens

• Unlike the mirrors, lenses have got two principal foci

one on each side of the lens and the nodal point is

situated within the substance of the lens just at the

centre. If the image is situated on the other side of the

object, it is called a Real Image and if it is on the

same side it is called a Virtual Image.

Page 133: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 133

The point at which the principal plane and principal axis intersect is

called the principal point or nodal point. Rays of light passing through

the nodal point are undeviated.

Light parallel to the principal axis is converged or diverged from the

point F, the principal focus.

Page 134: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 134

Image form by lens

• For, an object in any position, the image can be

constructed using two rays:

1) A ray from the top of the object which passes through

the principal point/nodal point.

2) A ray parallel to the principal axis, which after

refraction passes through (convex) or away from

(concave) the second principal focus.

Page 135: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 135

Page 136: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 136

• Convex lenses are thicker at the middle. Rays of light that pass

through the lens are brought closer together (they converge). A

convex lens is a converging lens.

• When parallel rays of light pass through a convex lens the

refracted rays converge at one point called the principal focus.

• The distance between the principal focus and the centre of the

lens is called the focal length.

Page 137: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 137

Page 138: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 138

Use of Convex Lenses

Use of Convex Lenses – The Camera

A camera consists of three main parts.

I. The body which is light tight and contains all the mechanical

parts.

II. The lens which is a convex (converging) lens.

III. The film or a charged couple device in the case of a digital

camera.

Page 139: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 139

Page 140: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 140

Use of Convex Lenses – The Camera

• The rays of light from the person are converged by the convex lens forming an image on the film or charged couple device in the case of a digital camera.

• The angle at which the light enters the lens depends on the distance of the object from the lens. If the object is close to the lens the light rays enter at a sharper angled. This results in the rays converging away from the lens. As the lens can only bend the light to a certain degree the image needs to be focussed in order to form on the film. This is achieved by moving the lens away from the film.

Page 141: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 141

Use of Convex Lenses – The Camera

• Similarly, if the object is away from the lens the rays enter at a wider angle. This results in the rays being refracted at a sharper angle and the image forming closer to the lens. In this case the lens needs to be positioned closer to the film to get a focused image.

• Thus the real image of a closer object forms further away from the lens than the real image of a distant object and the action of focusing is the moving of the lens to get the real image to fall on the film.

• The image formed is said to be real because the rays of lighted from the object pass through the film and inverted (upside down).

Page 142: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 142

The Magnifying Glass

A magnifying glass is a convex lens which produces a magnified

(larger) image of an object.

• A magnifying glass produces an upright, magnified virtual

image. The virtual image produced is on the same side of the

lens as the object. For a magnified image to be observed the

distance between the object and the lens must be shorter than

the focal length of the lens.

Page 143: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 143

For a magnified image to be observed the distance

between the object and the lens has to be shorter than

the focal length of the lens. The image formed is

upright, magnified and virtual.

Page 144: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 144

Magnification :The magnification of a lens can be

calculated using the following formula;

Page 145: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 145

Page 146: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 146

Aspheric lens

• An aspheric lens or asphere is a Lens whose surface

profiles are not portions of a sphere or cylinder.

• The asphere's more complex surface profile can

reduce or eliminate spherical aberration and also

reduce other optical aberration compared to a simple

lens.

Page 147: Dr Md Anisur Rahman Optics basics concepts

PHYSICAL PROPERTIES OF LIGHT

1) Polarization 2) Interference

3) Diffraction 4) Superimposition

Page 148: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 148

Polarization

Since a light wave’s electric field vibrates in a

direction perpendicular to its propagation motion, it is

called a transverse wave and is polarizable.

A sound wave, by contrast, vibrates back and forth

along its propagation direction and thus is not

polarizable.

Page 149: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 149

What is Polarization?

Light waves are travelling may or may not be parallel

to each other. If directions are randomly related to

each other the light is UNPOLARIZED/ NONPOLARIZED.

If parallel to each other is called POLARIZED.

Page 150: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 150

Non polarized light

NON POLARIZED

LIGHT

Page 151: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 151

Polarized light

POLARIZED LIGHT

Page 152: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 152

Polarized light

Page 153: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 153

How light is polarized?

Polarized light is produced from ordinary light by an

encounter with a polarizing substances or agent.

Polarizing substances, e,g. calcite crystal, only

transmit light rays which are vibrating in one

particular plane. Thus only a proportion of incident

light is transmitted onward and the emerging light is

polarized.

Page 154: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 154

How light is polarized?

A polarizing medium reduces radiant intensity but

does not affect spectral composition.

In nature, light is polarized on reflection from a plane

surface. Such as water, if the angle of incidence is

equal to the polarizing angle for the substances. The

polarizing angle is dependent on the refractive index

of the substance.

Page 155: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 155

Application of polarized light

Polarized sunglasses to exclude selectively the

reflected horizontal polarized light. Such glasses are

of great use in reducing glare from the sea or wet

roads.

Instruments: (to reduced reflected glare from the

cornea) example: Slit lamp Ophthalmoscope

Page 156: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 156

Application of polarized light

Binocular vision polarizing glass – May be used to

dissociate the eyes i,e in Titmus test

Also used in pleoptic to produced Haidinger’s

brushes and in optical lens making to examine lens

for stress.

Page 157: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 157

Birefringence

Some substances have double refractive index though

they transmit light into 2 direction and they are called

Birefringence

A widely used birefringent material is Calcite Its

birefringence is extremely large, with indices of

refraction for the o- and e-rays of 1.6584 and 1.4864

respectively.

Page 158: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 158

Calcite Crystal

Page 159: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 159

Applications of Birefringence

Birefringence finds use in the following applications:

Polarizing prisms and retarder plates

Liquid crystal displays

Medical Diagnostics

Page 160: Dr Md Anisur Rahman Optics basics concepts

2. Interference

Before discussing interference we should have clear

idea about wave properties of light.

Page 161: Dr Md Anisur Rahman Optics basics concepts

05/02/2023 [email protected] 161

Picture of a light wave

Page 162: Dr Md Anisur Rahman Optics basics concepts

05/02/2023 [email protected] 162

The maximum value of the wave displacement is called the amplitude (A) of the wave.

The cycle starts at zero and repeats after a distance. This distance is called the wavelength (λ).

Light can have different wavelengths. The inverse of the wavelength (1/λ) is the wave number (ν), which is expressed in cm–1.

Page 163: Dr Md Anisur Rahman Optics basics concepts

05/02/2023 [email protected] 163

The wave propagates at a wave speed (v). This wave

speed in a vacuum is equal to c, and is less than c in a

medium.

At a stationary point along the wave, the wave passes

by in a repeating cycle. The time to complete one

cycle is called the cycle time or period

Page 164: Dr Md Anisur Rahman Optics basics concepts

05/02/2023 [email protected] 164

Another important measure of a wave is its

frequency (f). It is measured as the number of

waves that pass a given point in one second. The unit

for frequency is cycles per second, also called hertz

(Hz).

Page 165: Dr Md Anisur Rahman Optics basics concepts

• As we can see, the frequency and the period are

reciprocals of one another. If the wave speed and

wavelength are known, the frequency can be

calculated.

Page 166: Dr Md Anisur Rahman Optics basics concepts

05/02/2023 [email protected] 166

Wave like model of Light

• The particle-like model of light describes large-scale effects

such as light passing through lenses or bouncing off mirrors.

• However, a wavelike model must be used to describe fine-

scale effects such as interference and diffraction that occur

when light passes through small openings or by sharp edges.

• The propagation of light or electromagnetic energy through

space can be described in terms of a traveling wave motion.

Page 167: Dr Md Anisur Rahman Optics basics concepts

05/02/2023 [email protected] 167

The wave moves energy—without moving mass—from one place

to another at a speed independent of its intensity or wavelength.

This wave nature of light is the basis of physical optics and

describes the interaction of light with media. Many of these

processes require calculus and quantum theory to describe them

rigorously.

Page 168: Dr Md Anisur Rahman Optics basics concepts

05/02/2023 [email protected] 168

Characteristics of light waves

• To understand light waves, it is important to understand basic

wave motion itself. Water waves are sequences of crests (high

points) and troughs (low points) that “move” along the surface

of the water. When ocean waves roll in toward the beach, the

line of crests and troughs is seen as profiles parallel to the

beach. An electromagnetic wave is made of an electric field

and a magnetic field that alternately get weaker and stronger.

Page 169: Dr Md Anisur Rahman Optics basics concepts

05/02/2023 [email protected] 169

Characteristics of light waves

• The directions of the fields are at right angles to the direction

the wave is moving, just as the motion of the water is up and

down while a water wave moves horizontally.

Page 170: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 170

2. Interference

• When two light waves from different coherent

sources meet together, then the distribution of energy

due to one wave is disturbed by the other. This

modification in the distribution of light energy due to

super- position of two light waves is called

"Interference of light"

Page 171: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 171

Conditions for Interference

 The two sources of light should emit continuous

waves of same wavelength and same time period i.e.

the source should have phase coherence.

The two sources of light should be very close to each

other. The waves emitted by two sources should

either have zero phase difference or no phase

difference.

Page 172: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 172

Page 173: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 173

Coherent sources

Those sources of light which emit light waves continuously of same wavelength, and time period,    frequency and amplitude and have zero phase difference or constant phase difference are coherent    sources.

Page 174: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 174

Types of interference

There are two types of interference.

1) Constructive interference. 

2)  Destructive interference

Page 175: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 175

Interference

constructive interference destructive interference

Page 176: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 176

Interference

Resultant of constructive interference

Resultant of destructive interference

constructive interference destructive interference

Page 177: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 177

constructive interference

When two light waves superpose with each other in

such away that the crest of one wave falls on the crest

of the second wave, and trough of one wave falls on

the trough of the second wave, then the    resultant

wave has larger amplitude and it is called

constructive interference

Page 178: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 178

destructive interference

When two light waves superpose with each other in

such away that the crest of one wave coincides the

   trough of the second wave, then the amplitude of

resultant wave becomes zero and it is called

  destructive interference.

Page 179: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 179

Diffraction

The term diffraction, from the Latin diffringere, 'to

break into pieces', referring to light breaking up

Page 180: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 180

Concept of diffraction

Diffraction is the bending of waves around obstacles,

or the spreading of waves by passing them through an

aperture, or opening.

Any type of energy that travels in a wave is capable

of diffraction, and the diffraction of sound and light

waves produces a number of effects.

Page 181: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 181

Concept of diffraction

Diffraction of light waves, is much more complicated, and has a number of applications in science and technology, including the use of diffraction gratings in the production of holograms.

Page 182: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 182

Diffraction of light

Page 183: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 183

Observing Diffraction in Light

• Wavelength of light plays a role in diffraction; so,

too, does the size of the aperture relative to the

wavelength. Hence, most studies of diffraction in

light involve very small openings, as, for instance, in

the diffraction grating.

• But light does not only diffract when passing through

an aperture, it also diffracts around obstacles.

Page 184: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 184

Observing Diffraction in Light

• When light passes through an aperture, most of the

beam goes straight through without disturbance, with

only the edges experiencing diffraction. If, however,

the size of the aperture is close to that of the

wavelength, the diffraction pattern will widen. when

light is passed through extremely narrow openings,

its diffraction is more noticeable.

Page 185: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 185

Diffraction Grating

• A diffraction grating is an optical device that consists of not

one but many thousands of apertures: Rowland's machine used

a fine diamond point to rule glass gratings, with about 15,000

lines per in (2.2 cm). Diffraction gratings today can have as

many as 100,000 apertures per inch.

Page 186: Dr Md Anisur Rahman Optics basics concepts

• The apertures in a diffraction grating are not mere

holes, but extremely narrow parallel slits that transform

a beam of light into a spectrum.

• Each of these openings diffracts the light beam, but

because they are evenly spaced and the same in width,

the diffracted waves experience constructive

interference.

Page 187: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 187

• This constructive interference pattern makes it

possible to view components of the spectrum

separately, thus enabling a scientist to observe

characteristics ranging from the structure of atoms

and molecules to the chemical composition of stars.

Page 188: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 188

• You may also notice that the light is alternately bright

and dark as you look through the curtain. This is

from interference. The bright places are where light

waves are adding together. The dark places are where

the waves cancel. With visible light, interference

always occurs with diffraction.

Page 189: Dr Md Anisur Rahman Optics basics concepts

May 2, 2023 [email protected] 189