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'.