SOME EXAMPLE OF TOTAL INTERNAL REFLECTION IN DAILY LIFE

1-) SPARKLING VISION OF A TEST TUBE PARTIALLY FILLED WITH WATER : Rays of light fall on the test tube where there is no water and gets reflected into air. As the test tube is tilted gradually, angle of incidence also increases. When the angle of incidence becomes more than 49, then total internal reflection takes place from this part of the test tube and it glows like silver. 

If test tube is completely  filled with water, then it does not happen because now critical angle becomes more than 49 and hence total internal reflection does not take place.

2-) BRILLIANCY OF DIAMOND : Refractive index of diamond with respect to air is 2.4 and critical angle for diamond and air is 24. When light falls on diamond it gets refracted and enters in it. The surface of the diamond are cut in such a way that, inside the diamond, the ray striking the surface makes an angle of incidence always greater than 24. Due to this, multiple total internal reflections takes place inside the diamond and the ray comes out in specific direction. If we look at from this direction then it appears shining.

3-) SPARKLING OF A CRACK IN GLASS : When the glass is cracked, then a thin layer is formed in cracking. Due to total internal refraction, the crack in glass is sparkled. 

4-) A PENCIL DIPPED IN WATER APPEARS TO BE SHORT AND BENT AT THE SURFACE IF SEEN FROM SIDE : A straight pencil is immersed in water. The portion BC appears to be shorten and bent as BC'. It is due to refraction. Virtual image of C formed at C'. Thus part BC appears to be BC'. Thus portion of stick under water appears to be raised and bent at point B.

5-) THE MIRAGE : On the hot summer day, a traveler in a desert region often sees a water with the trees and sky reflected in it, a short distance ahead of him. As he goes ahead, the lake disappears and he finds only a tree in the hot sand. This optical illusion is called mirage. Mirage can even be seen on road on a hot summer day the road at a distance appears to be covered with water, and we can see the reflection of sky and other objects from a distance. But as we approach the place where the water appears to be, we find that there is no water at all, and that it was just an illusion.  The phenomenon of mirage is produced by the total internal reflection of light which takes place when light passes from optically denser cold air to optically rarer hot air in the atmosphere.

6-)LOOMING : In cold countries the image of ship appears hanging inverted in air. This phenomenon is called looming. 

The layer of air in contact with earth is cooler and denser than layers above. so rays of light coming from ship pass from denser to rarer layers progressively and they get deviated away from the normal. so angle of incidence for every layer successive layer goes on increasing. A stage is reached when this angle and ray gets totally internally reflected. After reflection it reaches viewer's eye. To the viewer it appears that the whole ship is hanging in the air.

ELECTRICAL ENERGY

 Electric energy :

 The electric energy or commonly called electricity is used to drive a variety of equipments.

Sources of electrical energy :

There are number of ways to convert different forms of energy into electrical energy: 

1-) Electro Dynamo: This equipment converts mechanical energy into electrical energy. In this, an enclosed coil is rotated in the magnetic field, as a result due to electro-magnetic induction electricity is generated. 

2-) Electric Cell: In this chemical energy is converted into electrical energy. Examples are dry cell, lead battery, Ni-Fe battery etc.

3-) Photo Electric Cell: In this light energy is converted into electric energy. Most common example is use of solar cells that convert solar energy to electricity. Silicon is used in making solar cells. Artificial satellites use solar cells as main sources of energy.

4-) Thermo-Couple: In this apparatus a closed circuit is made by joining the ends of antimony and bismuth rods. Both the joints of this circuit when placed at two different temperatures an electromotive force is produce in the circuit resulting in flow of electric current in the circuit. 

ELECTRICITY

In our daily life we commonly use the term energy in a variety of sense, for example we say, an atheletes body is full of energy, a glass of milk provides the child energy, burning of gas gives energy to cook our meal or burning of fuels gives energy to drive a vehicles etc. In conclusion we can say that energy is such an entity which is needed for doing any work or any object that has capacity to do work is having energy.

There are a number of sources where form energy can be harvested. The basic principle is that different forms of energy can be interconverted. The most ancient sources of energy is Sun and then come wood or coal which upon burning provide energy to cook meals. This sources has replaced by petroleum gas to some extent. Besides, kerosine oil, petrol, diesel, etc. are also conventional sources of energy. The other sources of energy include harvesting of energy of flowing water by mechanical means into electrical energy ,wind mills converted wind energy to electrical energy, conversion of solar energy through solar cells into electrical energy. The process of nuclear fission produces energy in nuclear power plants.

DEFECTS OF VISION

A normal eye can see all objects situated at a distance greater than 25 cm. using its power of accommodation. But due to certain abnormalities, elongation, distortion or even distortion of eye ball, the defects of vision arise and the eyes become unable to accommodate itself to various distances, then it is said to be defective. The defects are mainly of five types;

1-) Short-sightedness or Myopia, 

2-) Long-sightedness or Hypermetropia,

3-) Old sight or Presbyopia,

4-) Astigmatism,

5-) Colour blindness.

IMAGE FORMATION BY HUMAN EYE

The light entering into the eye gets reflected at the cornea and passes through aqueous humour. Through aqueous humuor light incidents on the lens and then it passes through vitreous humour and falls on retina where real and inverted image is formed. Brain sets the sensation received to size and inverts the figure just symmetrical to the object. 

POWER OF ACCOMODATION

The ability of an eye to focus the distant objects as well as the nearly objects on the retina by changing the focal length or converging power of its lens, is called power of accommodation. 

 

HUMAN EYE

The eye is the organ that allows us to see the world around us. It is perhaps the most wonderful and perfect optical instrument. Without eye, all other optical instruments would have no value at all. 

The main part of the human eye are : cornea, iris, pupil, eye-lens, aqueous humour, optical nerve, blind spot, retina and ciliary muscles.

1- Sclerotic: The human eye is a dark spherical chamber filled with a transparent fluid. It consists of an eye ball having a diameter of about 25mm. The walls of the eye ball consist of two major layers. The outer covering is known as "Sclerotic layer". It is tough opaque white substances. It forms the white portion of the eye.

2-Cornea: The front of this coating forms a curved section known as "Cornea". It is made of a transparent substance and is bulging outwards. The light coming from objects enters the eye through cornea. 

3-Iris: Just behind the cornea is the iris( or coloured diaphragm
) . The colour of iris is different for different individuals depending upon the pigments present in it. 

4-Pupil: There is a hole in the middle of the iris which is called Pupil of the eye. The pupil dilates or contracts depending upon the amount of light available.

 5-Eye lens: Behind the pupil and the iris is the eye lens. It is a convex lens made of a transparent material like jelly, made of proteins. The eye lens is kept in its position by a strong elastic frame made of 'ciliary muscles'. The focal length of eye lens can be changed by the action of ciliary muscles.

6-Retina: The screen of the eye ball where the images of the objects are formed, is called 'Retina'. It is located behind the eye lens at the back portion of the eye. The retina is a highly sensitive surface made up of nerves, rods and cones and communicates with the brain through the optic nerve. The least sensitive part of  the retina is called as the  'blind spot' and most sensitive point is called as the 'yellow spot'. 

USES OF LENSES

(A) CONCAVE LENS : 

1-) Concave lens are used in a variety of instruments e.g., microscope,telescope,photographic camera, film projector etc. 

2-) To view the smallest parts of watch by watch maker. 

3-) To detect eye and ear defects by a doctor. 

4-) To remove the defect of hypermetropia.

(B) CONVEX LENS :

1-) In the construction of Gallileo's telescope.

2-) To remove the defect of myopia. 

IDENTIFICATION OF CONVEX AND CONCAVE LENSES

1-)  By Touching : The convex lens is thicker at the centre relative to its edges, while the concave lens is thinner at the centre than its edges. 

2-) By Image Formation : On viewing the distant objects by convex lenses the image is seen as inverted and diminished. In case of concave lenses, the images is erect  and diminished. 

On viewing the near object, e.g., printed matter in a book, it looks lager by convex lenses whereas the same appears smaller by concave lenses.

In case of a rectangular glass plate, unlike lenses, the near and far objects appear the same as they are.

LENSES

Any transparent refracting medium bounded by two surfaces ( in which at least one surface should be curved surface)is called a "lens". The lenses used in laboratory are generally made up off glass. There are two type of lenses :  

1-) Convex lenses : These lenses are thicker at the centre and thinner at their edges. These are also called converging lenses. There are three type of convex lens :

a-) Double convex or biconvex 

b-) Plano-convex 

c-) Concavo-convex 

2-) Concave lenses : These lenses are thinner at the centre than at edges. A concave lens is also called as diverging lens. There are three type of concave lenses : 

a-) Double concave or biconcave 

b-) Plano-concave

c-) convexo-concave 

 

DOUBLE REFRACTION

When a beam of light of unpolarized light is allowed to pass through a calcite crystal, it is split up into two refracted beams in place of the usual one as in glass. This phenomenon is known as double refraction and was first discovered by a Dutch philosopher Erarmus Bartholinus in the year 1669. 

PLANE POLARIZED LIGHT BY REFLECTION

The simplest way to produce plane polarized light is by reflection. It was discovered by Malus in 1808 that partially polarized light is obtained when ordinary light is reflected from the surface of a transparent medium like glass or water and that the degree of polarization varies with the angle of incidence. At a certain angle of incidence, depending upon the nature of the reflecting surface, the reflecting light has the greatest percentage of the polarized light. This angle of incidence is called the angle of polarization for that medium and for ordinary glass its value is 57.5*. As the refractive index depends upon the wavelength, the angle of maximum polarization varies with the wavelength and hence the complete polarization is possible with monochromatic light and not with white light. 

METHODS TO PRODUCE PLANE- POLARIZED LIGHT

Various method to produce plane polarized light may be broadly summarized as below: 

1-) Polarization by reflection 

2-)Polarization by refraction

3-)Polarization by double refraction

4-) Polarization by selective absorption by crystals 

POLARISATION OF LIGHT

The phenomenon of interference and diffraction have proved beyond any doubt that light is some from of wave motion. But these properties of do not tell us whether the waves so essential for explaining these phenomena are longitudinal or transverse. Also regarding the nature of vibrations(whether linear, circular, elliptical or torsional) no clue is provided by these phenomena. It is the phenomenon of polarisation which could decide this question and show that waves are definitely transverse in nature.

 

plane polarized light:

When ordinary light is allowed to pass through a tourmaline crystal, the vibrations are confined only to one direction of propagation of light. This light which has acquired the property of one sidedness and the vibrations are linear is called "plane polarized or linearly polarized light". 

DIFFRACTION OF LIGHT

It is a matter of common experience that the sound waves or water escaping through a small hole spread out in all directions as if they originated at the hole. After passing through the hole all waves do not propagate in its original direction but a part of it is bent, the wave fronts for the ripples being semicircles with their centres situated at the centre of the hole. This phenomenon is called "diffraction" and is an essential characteristic of all wave motions.

In a similar way, when a beam of light passes through a small opening, it also deviated from its rectilinear path and does bend round the corner as other types of waves do but the amount of this bending is extremely small. The small bending in case of light is due to its very small wavelength of the order 6000A. The wavelength of ordinary sound waves is nearly 60cm. Consequently the diffraction in case of light is .000001 fold less, a small obstacle will obstruct the path of light whereas a much lager obstacle will be required to achieve the same effect in sound.

 

                                                                                                                                  

INTERFERENCE OF LIGHT

When two or more waves passes through a medium; its particles are affected by each wave independently. At an instant, the resultant displacement of a particle is the algebraic sum of the displacements due to each wave and depends upon the phase difference. This is known as the principle of superposition and is the foundation of the theory of interference developed by young in 1801. If a single source of light is present in the medium, then the energy distribution is uniform. However, if there are two adjacent exactly similar sources, then the distribution no longer remains uniform. At some places the energy is maximum while at other places the energy is minimum. Of course the total energy of the system remains  the same. This modification in energy distribution due to presence of two or more exactly similar sources is a specific case of superposition of waves and is known as "INTERFERENCE" . 

TOTAL INTERNAL REFLECTION

If the angle of incidence is further increased beyond the critical angle, then ray instead of being refracted gets totally internally reflected according to law of reflection. This phenomenon is called 'TOTAL INTERNAL REFLECTION". 

CONDITIONS FOR TOTAL INTERNAL REFLECTION : 

1- The ray must passes from a denser to a rarer medium.

2- The angle of incidence in the denser medium must be greater than the critical for that particular medium. 

CRITICAL ANGLE

When a ray of light enters from a denser medium to a rarer medium, its some part is reflected and most of  part is refracted. in this condition, the angle of refraction is greater than angle of incidence.

As the angle of incidence  gradually increased the corresponding angle of refraction also increases. At a certain angle of incidence the angle of refraction becomes 90*. This angle of incidence is called the "CRITICAL ANGLE" for the given pair of media. 

"critical angle is the angle of incidence in the denser medium corresponding to which the angle of refraction in the rarer medium is 90*" It is denoted by C. 

REFRACTION OF LIGHT

When light passes from one medium to another medium, its velocity changes. Due to change in velocity a ray of light is deviated from its path when it falls on the surface of second medium obliquely. This phenomenon is called "REFRACTION OF LIGHT". 

when ray of light inters a denser medium from a rarer medium,  bends towards the normal whereas it bends away from the normal when it enters a rarer medium from denser medium.

LAWS OF REFRACTION :

There are two laws of refraction 

1- The incident ray, the refracted ray and the normal at the point of incidence lie in the same plane. 

2- The ratio of the sine of angle of incidence to the sine of angle of refraction is a constant for any two given media and for the same colour of light. This constant ratio is called the "refractive index "of the second medium with respect to the first medium. The second law of refraction is also called "snell's law".

REFLECTION OF LIGHT

"When light is travelling in any medium, falls on the surface of a second medium, a portion of light is usually sent back into the first medium. This phenomenon is known as reflection."

The amount of reflected light depends upon the nature of reflecting surface. A smooth and polished surface reflects more light. If however, the reflecting surface is rough(unpolished) as in the case of a sheet of white paper or the walls of the room, then rays are reflected in all directions. This is known as diffused reflection. In practice a particular device, called mirror, used for reflection. A mirror is a device which reflects most of the light falling on it.

laws of reflection :

The reflection of light takes place with the following laws - 

1- The incident ray, the reflected ray and the normal at the point of incidence are in the same plane 

2- The angle of incidence is equal to angle of relection.  

THE LIGHT

THE LIGHT

Nature has provided us five important sense organs. The sense of  'sight' enables us to see a verity of objects in the world around us. However, we cannot see anything in dark. During the day, the sunlight and at the artificial light helps us to see objects. when light falls on an object, it is reflected from the surface of the object. This reflected light when received by our eyes, enables us to see things. " light is electromagnetic rediation of a wavelenght that is visible to human eye (in the range from about 380-400 nm to about 760-780 nm). light can travel through a vacuum. In vacuum and air the speed of light is 3 lakh km/sec

    

sources of light which emit light by themselves are called " Luminous bodies ". The sun, hot filament of the electric bulb, candle flame, etc. are some examples of luminous bodies