The construction and working of the human eye is similar to photographic camera in many respects. Human eye is almost a spherical ball, with a light bulge in the front. The structure and function of each part of the eye is given below :
8 Sclerotic : It is the outermost covering of the eye ball. It is made of white tough fibrous tissues.
Its function is to house and protect the vital internal parts of the eye.
8 Cornea : It is the front bulging part of the eye. It is made of transparent tissues.
Its function is to act as a window to the world, i.e., to allow the light to enter in the eye ball.
8 Choroid : It is a grey membrane attached to the sclerotic from the inner side.
Its function is to darken the eye from inside and, hence, prevent any internal reflection.
8 Optic Nerve : It is a bundle of approximately 70,000 nerves originating from the brain and entering the eye ball from behind.
Its function is to carry optical messages (visual messages) to the brain.
8 Retina : The optic nerve on entering the ball, spreads like a canopy, such that each nerve end attaches itself to the choroid. The nerve endings form a hemi-spherical screen called retina. These nerve endings on the retina are sensitive to visible light. On retina there are two important areas namely yellow spot and Blind spot.
The function of retina is to receive the optical image of the object and then convert it to optical pulses. These pulses are then sent to the brain through optic nerve.
8 Yellow spot : It is a small area, facing the eye lens. It has high concentration of nerve endings and is slightly raised as well as slightly yellow in colour.
Its function is to form a very clear image by sending a large number of optical pulses to brain.
8 Blind Spot : It is a region on the retina, where the optic nerve enters the eye ball. It has no nerve ending and hence, is insensitive to light.
It does not seem to have any function. Any image formed on this spot is not visible.
8 Crystalline lens : It is a double convex lens made of transparent tissues. It is held in position by a ring of muscles, commonly called ciliary muscles.
Its function is to focus the images of different objects clearly on the retina.
8 Ciliary Muscles : It is a ring of muscles which holds the crystalline lens in position . When these muscles relax, they increase the focal length of the crystalline lens and vice versa. Its function is to alter the focal length of crystalline lens so that the images of the objects, situated at different distances, are clearly focused on the retina.
8 Iris : It is a circular diaphragm suspended in front of the crystalline lens. It has a tiny hole in the middle and is commonly called pupil. It has tiny muscles arranged radially around the pupil. These muscles can increase or decrease the diameter of the pupil. The iris is heavily. pigmented. The colour of eyes depends upon colour of pigment.
The function of iris is to control the amount of light entering the eye. This is done by increasing or decreasing the diameter of pupil
8 Vitreous Humour : It is a dense jelly-like fluid, slightly grey in colour, filling the part of eye between crystalline lens and retina.
Its function is (i) to prevent the eye ball from collapsing due to change in atmospheric pressure, (ii) in focusing the rays clearly on the retina.
8 Aqueous Humour : It is a watery, saline fluid, filling the part of the eye between the cornea and the crystalline lens.
Its function is (i) to prevent front part of the eyeball from collapsing with the change in atmospheric pressure, (ii) to keep the cornea moist.
When the object is infront of eye then light rays coming from the object are refracted and after passing through the vitreous humour they are focused on the retina. The sensation from retina is conveyed to the brain through the optic nerves and the object becomes visible.
When eye is in normal condition i.e. the muscles are not strained then a clear image of the objects situated at infinity is formed on the retina. This is possible only when the distance between lens and retina is equal to the focal length of the lens(fig). When the object is close to the eye then its image should be formed behind the retina and it should by blurred, but it is not so in reality. Because when the object is close to eye then muscles are strained automatically. Muscles get contracted to make lens thicker at the centre which reduces the focal length of the lens and image is again formed on the retina. The ability of self adjustment of focal length of the eye lens is called accommodation power.
Abnormalities in the normal vision of the eye are called defects of vision or defects of eyes.
The most commonly observed defects of vision (or defects of eyes) are:
(i) Myopia or shortsightedness or nearsightedness
(ii) Hypermetropia or longsightedness or hyperopia or farsightedness
(iii) Astigmatism
Shortsightedness (or myopia) is the defect due to which the eye is not able to see the distant objects clearly though it can see the nearby objects clearly.
So, a shortsighted or myopic eye has its far point nearer than infinity.
What causes shortsightedness (or myopia)
Myopia or shortsightedness is caused by the following reasons.
(a) Decrease of focal length of the eye lens, i.e. the eye lens becomes more convergent.
(b) Elongation of the eyeball, i.e. the increased length of the eyeball.
How is shortsightedness (or myopia) corrected ?
The shortsightedness (myopia) can be corrected by making the eye lens less convergent. This can be
done by placing a concave lens (divergent lens) of suitable focal length before the eye lens.
The rays of light coming from a distant object after passing through the concave (diverging) lens of the spectacles diverge slightly. As a result, the rays entering the eye appear to come from the far point of the myopic eye, and therefore get focused at the retina to form a clear image.
How to calculate the focal length and power of the lens used for correcting a myopic eye
The corrective lens (concave lens) needed to correct a myopic eye should form the image of the far-off object (e.g. at infinity) at the far point (d) of the myopic person.
Thus, u = – , v = –d, f = ?
f = – d
The longsightedness (or hypermetropia) is the defect due to which the eye is not able to see clearly the nearby objects though it can see the distant objects clearly.
So, a longsighted eye has its near point farther away from the normal near point (about 25 cm for an adult).
What causes longsightedness (or hypermetropia)
Hypermetropia or longsightedness is caused due to the following reasons:
(i) Increase of the focal length of the eye lens, i.e. the eye lens becoming less convergent.
(ii) Shortening of the eye ball, i.e. the length of the eye ball has decreased.
How is longsightedness (or hypermetropia) corrected
Longsightedness (hypermetropia) can be corrected by making the eye lens more convergent. This is generally done by placing a convex lens (converging lens) of suitable focal length before the eye lens. This is shown in Fig.
The rays from a nearby object (about 25 cm) after passing through the convex lens of the spectacles converge slightly. As a result, the rays entering the eye appear to come from the near point of the longsighted eye, and therefore get focused at the retina to form a clear image.
How to calculate the focal length and power of the lens used for correcting a hypermetropic eye
The corrective lens (a convex lens) needed to correct a hypermetropic (or longsighted) eye should form the image of the object placed at the normal near point (the least distance of distinct vision is 25 cm) at the near point of the hypermetropic person. Thus,
v = Near point distance of the hypermetropic eye = – d
u = Near point distance for the normal eye = – D = – 25 cm Using the lens formula,
This defect arises due to different sections of cornea having different radii of curvature. One section of cornea may be more sharply curved that the other. The man cannot focus on both horizontal and vertical line simultaneously.
For remedy a cylindrical lens with the axis of the cylindrical lens parallel to the correct axis of the cornea, is used.
If along with astigmatism, myopia or hypermetropia is also associated, which is generally very common, then for the complete remedy of the defect, sphero-cylindrical (or compound) lens are used.
Eye with this defect is unable to see the lines in different axes but at the same distance with same clarity. It occurs due to irregular curvature of cornea/by birth or arises due to some injury. Horizontal and vertical lines can't be seen simultaneously with this defective eye. Object in one direction get well focused and in perpendicular direction remain blurred.
Correction: In this case, the spectacles are cylindrical lenses of suitable focal length.
This defect is usually found in older persons. Due to stiffening of ciliary muscles, controlling the curvature of the lens reduces, thus the eye loses much of its accommodating power.
As a result distant as well as nearby objects cannot be seen clearly in proper perspective. That is, in this defect near point as well as far point of the eye is affected. For the remedy of this defect two separate lenses or one bifocal lens is used. For visualizing nearby objects, convex lens is used, where as for seeing distant objects concave lens is used.
A homogeneous solid transparent and refracting medium bounded by two plane surfaces inclined at an angle is called a prism :
3-D View
Refraction through a prism :
(a) PQ and PR are refracting surfaces.
(b) ÐQPR = A is called refracting angle or the angle of prism (also called Apex angle.)
(c) d = angle of deviation
(d) For refraction of a monochromatic (single wave length) ray of light through a prism;
d = (i + e) – (r1 + r2) and r1 + r2 = A
\ d = i + e – A.
Sir Isaac Newton, while working with an astronomical telescope, observed that the images of stars as seen through the telescope were coloured near the fringes. He got the lenses of the telescope polished, but found that the colour still persisted. From the above observation, he concluded that the fault may not be with the lenses, but it had something to do with the nature of light itself. To investigate this conclusion, he performed the following experiment.
Experiment: Newton allowed sunlight to enter through a small hole in a window of a darkened room. He placed an equilateral prism in the path of the narrow beam of light. The light emerging from the prism was allowed to fall on the white screen. It was found that light received on the white screen was a band of seven colours. The order of colours from the base of prism is violet, indigo, blue, green, yellow, orange and red. This order of colours can be easily remembered by remembering the word VIBGYOR.
(a) Dispersion : The phenomenon due to which white light splits into seven colours (VIBGYOR), when passed through an equilateral prism is called dispersion.
(b) Spectrum: The band of seven colours obtained on the screen, when white light splits into seven colours is called spectrum.
What is meant by monochromatic and polychromatic light
The light of one single colour, or of one single wavelength is called monochromatic light (chrome means colour). Sodium light is golden yellow in colour. So, sodium light is monochromatic light.
The light made up of many colours, or light consisting of radiations of many wavelengths, is called polychromatic light. White light is made up of seven colours. So, white light (or sunlight) is a polychromatic light.
How is the dispersed white light recomposed
Recombination of the seven colours of the dispersed white light to get white light is called recomposing of the dispersed white light.
How does a rainbow form
Rainbow is an example of the dispersion of white light.
Just after the rain, a large number of small droplets of water remain suspended in the air. Each drop acts like a small prism. When sunlight falls on these drops, the white light splits into seven colours. The dispersed light from a large number of drops forms a continuous band of seven colours. This coloured band is called rainbow. Thus, rainbow is produced due to dispersion of white light by small raindrops hanging in the air after the rain.
The rainbow is seen when the sun is behind the observer.
When light falls on tiny particles then diffused reflection takes place and light spreads in all possible direction. This phenomenon is known as scattering of light.
Small particles scatter mainly blue light. When size of the particle increases then the light of longer wavelength also scatter. The path of a beam of light passing through a true solution is not visible. However, its path becomes visible through a colloidal solution where the size of the particles is relatively larger.
Rayleigh proved that the intensity of scattered light is inversely proportional to the fourth power of the wavelength, provided the scatters is smaller in size than the wavelength of light:
scattering 
(a) Tyndall Effect: The earth's atmosphere is a heterogeneous mixtures of minute particles. These particles include smoke, tiny water droplets, suspended particles of dust and molecules of air. When a beam of light strikes such fine particles, the path of the beam becomes visible.
The light reaches us after being reflected diffusely by these particles. The phenomenon of scattering of light by the colloidal particle gives rise to tyndall effect. This phenomenon is seen when a fine beam of sunlight enters a smoke filled room through a small hole. Thus, scattering of light makes the particles visible. Tyndall effect can also be observed when sunlight passes through a canopy of a dense forest. Here, tiny water droplets in the mist scatter light.
(b) Phenomena based upon Scattering of Light: A number of optical phenomena can be explained on the basis of scattering of light:
(i) Colour of the clear sky is blue: When we look at the sky, we receive sunlight scattered by fine dust particles, air molecules and water-vapour molecules present in the atmosphere. Since blue light, which is present in larger proportion of the violet light in the sunlight, is scattered about ten times more than the orange-red light, the light reaching the eye is mainly blue. Hence the sky appears bluish.
If the earth had no atmosphere, there were no scattered sunlight and the sky would have appeared black. In fact, the sky does appear black to the astronauts in the space above the earth's atmosphere.
(ii) The clouds appears white: The dependence of scattering on 1/l4 is valid only when the scatterer particles or molecules are much smaller than the wavelength of light, as are air molecules. Clouds, however, contain water droplets or ice crystals that are much larger than l and they hence scatter light of all wavelengths nearly equally. Hence clouds appear white.
(iii) At sunrise or sunset the sun appears reddish: The scattering of light also explains the reddish appearance of sun at sunrise or sunset. At sunrise or sunset, the sun is near the horizon and the sunrays reach the earth after passing through a maximum distance in the atmosphere. During this passage, the light is scattered by air molecules and fine dust particles. Since scattering µ 1/l4, most of the blue and neighbouring coloured light is scattered out before reaching the observer. Hence the light received by the observer is predominantly red. (For a similar reason, the sun appears orange-red in fog or mist.)
At noon, when the sun is overhead, the sunrays travel minimum distance in the atmosphere and there is little scattering. Hence the sun appears almost while (infact, slightly yellowish because some blue light is scattered).
(C) Experimental verification of Scattering: Let us do an activity to understand the colour of sun at sunrise and sunset. Place a strong source (s) of white light at the focus of converging lens (L1). This lens provides a parallel beam of light to pass through a transparent glass tank (T) containing clear water. Allow the beam of light to pass through a circular hole (C) made in a cardboard. Obtain a sharp image of the circular hole on a screen (MN) using a second converging lens (L2).
Dissolve 200g of sodium thiosulphate in 2L of clear water taken in the tank. Add 1 to 2 mL of concentrated sulphuric acid to the water. We observe that microscopic sulphur particles precipitate in 2 to 3 minutes. As sulphur particles begin to form we can observe the blue light from the three sides of the glass tank.
It is due to scattering of short wavelengths by minute colloidal sulphur particles. We observe that the colour of the transmitted light from the fourth side of glass tank facing the circular tank at first is orange red colour and then bright crimson red colour on the screen.
Light from the sun near the horizon passes through thicker layer of air and larger distance in the earth's atmosphere before reaching our eyes. Light from the sun travel relatively short distance. At moon, the sun appears white.
As a little of blue and violet colours are scattered. Near the horizon, most of the blue light and shorter wavelength are scattered away by the particles. Therefore, the light that reaches our eyes is of longer wavelength. This gives rise to the reddish appearance of the sun.
Þ Kaleidoscope
The keleidoscope is a device that uses reflections to produce patterns. It consists of mirrors inclined to each other. The mirrors form multiple images of objects in front of them. This creates beautiful patterns, which change when the keleidoscope is rotated or shaken.
Þ Periscope
The working of a periscope is based on the principle of successive reflections from two plane mirrors. It consists of two plane mirrors M1 and M2 facing each other fixed at 45° to the framework of a tube which is bent twice at right angle (fig a). A beam of light from some object is turned through one right angle by the mirror M1. In the same way the light is deviated through another right angle by the mirror M2. Therefore, the object is seen by the eye in spite of the obstacle. This arrangement can be used by a person to see a match over the heads of a few people while standing at the back of the crowd.
Even an object can be seen through a wall as well by an arrangement as shown in fig.(b) In this case, light from the candle is reflected by four mirrors M1, M2, M3 and M4 before reaching the eye. Therefore, the candle is seen through the wall.
(a) Colour of objects in White and Coloured Light: We known that white light is a mixture of seven colours. Light can be of different colours. Let us understand that why different objects appear to have different colours. A rose appear red because when white light falls on rose, it reflects only the red component and absorbs the other components.
We conclude that the colour of an object depends upon the colour of light it reflects.
(i) If an object absorbs lights of all colours and reflects none, it appears black.
(ii) If an object reflects light of all colour, it appears white when seen in white light.
(iii) When we talk of colour of an object, we refer to its colour as seen in white light.
(iv) A rose will appear black in green light because there is no red component in the light and it will not reflect any light. Hence no light will come from rose to the eye. Similarly if a green leaf is seen in red light, it appears black.
(v) If a white flower is seen in red light, it appear red because a white object reflects light of all colours falling on it. So it reflects the red light falling on it, which then enters the eye.
(b) Primary Colours of Light: Red, green and blue are primary colours of light and they produce white light when added in equal proportions. All colours can be obtained by mixing these three colours in different proportions.
(c) Secondary Colours or Composite Colours of Light: The colours of light produced by adding any of primary colours are called secondary colours. Cyan, magenta and yellow are secondary colours of light.
Red + Green = Yellow
Green + Blue = Cyan
Red + Blue = Magenta
The method of producing different colours of light by adding the primary colours is called colour addition.
(d) Complementary Colours of Light: The lights of two colours which when added in equal proportions produce white light are called complementary colours of light and the two colours are called complements of each other.
For example, yellow and blue light are complementary colours of light because when they mixed in equal proportions, they produce white light. We can also find the pairs of complimentary colours of light as follows.
Complimentary colours:
(Red + Green) + Blue = Yellow + Blue = White
Red + (Green + Blue) = Red + Cyan = White
(Red + Blue) + Green = Magenta + Green = White
The above results can be diagrammatically represented in the form of a triangle as shown in figure. The outer limbs of the figure show the results of the addition of primary colours red, green and blue. The complementary colour pairs such as red and cyan are opposite to each other.
(e) Primary Colours of Pigment: Pigments are those substances that give colour to an object. The colour of a pigment as seen by us depends on what components of light it absorb or subtract from white light before reflecting that rest to our eyes. A primary colour (cyan, magenta, yellow) of a pigment is due to a primary colour of light being subtracted from white light.
White – Red – Blue + Green = Cyan
White – Green = Red + Blue = Magenta
White – Blue = Red + Green = Yellow
Mixing CMY (cyan, magenta, yellow) pigment in the correct proportions can produce millions of colour. If equal amount of pure
CMY pigments are mixed, we should get a black pigment.
However, printers use black ink in addition to CMY inks to get good results.
Q.1 What is meant by power of accommodation of the eye?
Ans. The ability of the eye lens to adjust its focal length is called accommodation of the eye. Power of accommodation of an eye is defined as the maximum variation in the power or focal length of the eye lens.
Q.2 A person with a myopic eye cannot see objects beyond 1.2m distinctly. What should be the type of the corrective lens used to restore proper vision?
Ans. Concave lens of focal length given by
or f = –1.2m or 
Q.3 What is the far point and near point of the human eye with normal vision?
Ans. The farthest position of an object from the human eye so that its sharp image is formed on the retina is at infinite distance from the eye.
The nearest position of an object from a human eye so that its sharp image is formed on the retina is at 25cm from the eye.
Q.4 A student has difficulty in reading the black board while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?
Ans. Near sighted or myopia. This defect can be corrected by using lens of suitable focal length.
Q.5 A person needs a lens of power –5.5 diopter for correcting distant vision. For correcting his near vision, he needs a lens of power +1.5 diopter. What is the focal length of the lens required for correcting (i) distant vision and (ii) near vision?
Ans. (i) 
(ii) 
Q.6 The far point of a myopic person is 150cm in front the eye. What is the nature and power of the lens required to correct the problem?
Ans. 
or f =–150cm
\ Power = 
The lens is concave lens.
Q.7 Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye is 1m. What is the power of the lens required to correct this defect? Assume that the near point of the normal eye is 25cm.
Ans. For diagram, refer figure 4.
or 
\ Power = 
Q.8 Why is a normal eye not able to see clearly the objects placed closer than 25 cm?
Ans. The nearest position of an object from normal human eye so that its sharp image of the object is formed on retina is 25cm. If the object is placed at a distance less than 25cm, then the blurred image of the object is formed on retina as the focal length of eye lens cannot by decreased below a certain limit. Hence, eye cannot see it clearly.
Q.9 What happens to the image distance in the eye when we increase the distance of an object from the eye?
Ans. The image distance remains the same in the eye because the eye has the ability to change the focal length of its lens to make the image always on the retina when the object distance increase from the eye?
Q.10 Why do stars twinkle?
Ans. Refer Theory
Q.11 Explain why the planets do not twinkle?
Ans. Refer Theory
Q.12 Why does the sun appear red early in the morning?
Ans. Refer Theory
Q.13 Why does the sky appear dark instead of blue to an astronaut?
Ans. The blue colour of sky is de to the scattering of sunlight. The scattering of sunlight in the atmosphere is due to the presence of atoms and molecules of gas, dropets and dust particles. When the astronaut is in space, then there is no atmosphere (or atoms and molecules of gases, droplets and dust particles) around him. Therefore sunlight does not scatter and hence sky appears dark.
Q.14 A young boy can adjust the power of his eye-lens between 50D & 60D. His far point is infinity.
(a) What is the distance of his retina from the eye-lens?
(b) What is his near point?
Ans. (a) When the eye is fully relaxed, its focal length is largest and the power of the eye, lens is minimum. This power is 50D according to the given data. The focal length is 1/50m = 2cm. As the far point is at infinity, the parallel rays coming from infinity are focused on the retina in the fully relaxed condition. Hence, the distance of the retina from the lens equals the focal length which is 2cm.
(b) When the eye is focused at the near point, the power is maximum which is 60D. The focal length in this case is f = 60m = 5/3cm. The image is formed on the retina and thus v = 2cm. We have,
or
or u = –10cm
Q.15 What is the difference between images produced by a telescope and binoculars?
Ans. The image produced by telescope does not give perception of depth whereas the image produced by binoculars produces 3-dimensional image with increased field of view and intensity.
Q.16 A person cannot see objects clearly beyond 50cm. Find the power of the lens to correct the vision.
Ans. Here v = –50 mm, u = ¥. Hence using 
.
We find f = –50cm = 0.5m.
So power of the lens is P = 
Q.17 A myopic persons having far point 80cm uses spectacles of power –1.0D. How far can he see clearly?
Ans. Use 
Hence v = –80cm; f = +100cm
Hence 
or
This gives u = –400cm = –4cm
Q.1 What is meant by persistence of vision ? (2003)
Q.2 What kind of lens is used in the spectacles of a person suffering from myopia (near sightedness)? (2006)
Q.3 List three common defects of vision that can be corrected with the use of spectacles. (2006)
Q.4 Write the function of Iris in the human eye. (2007)
Q.5 To an astronaut, why does the sky appear dark instead of blue? (2008)
Q.6 Why does the sun appear reddish at sunrise? (2008)
Q.7 Why is red colour selected for danger signal lights? (2008)
Q.8 The far point of a myopic person is 80 cm in front of the eyes. What is the nature and power of the lens required to enable him to see very distant objects distinctly? (2003)
Q.9 Explain about the colour of the sun at sunrise and sunset. (2007)
Q.10 What are the conditions for formation of rainbow? (2003)
Q.11 Draw a labelled diagram of human eye.
What is power of accommodation of eye? Define colour blindness. (2005)
Q.12 (a) Draw a diagram to show the formation of image of a distant object by a myopic eye. How can such an eye defect be remedied ?
(b) State two reasons due to which this eye defect may be caused.
(c) A person with myopic eye cannot see objects beyond a distance of 1.5 m. What would be the power of the corrective lens used to restore proper vision ? (2008)
Q.13 What is long sightedness ? List two causes for development of long-sightedness. Describe with a ray diagram, how this defect may be corrected by using spectacles. (2005)
Q.14 (a) State two main causes of a person developing near sightedness. With the help of a ray diagram, suggest how he can be helped to overcome this disability ?
(b) The far point of a myopic person is 150 cm in front of the eye. Calculate the focal length and power of a lens required to enable him to see distant objects clearly. (2004)
Q.15 (a) Explain the following terms used in relation to defects of vision and corrections provided for them: (i) Myopia (ii) Astigmatism (iii) Presbyopia (iv) Far sightedness.
(b) Describe with a ray diagram how a person with myopia can be helped by spectacles. (2005)
Q.16 A 14 year old student is not able to see clearly the questions written on blackboard placed at a distance of 5 m from him. (a) Name the defect of vision he is suffering from. (b) With the help of labelled ray diagrams, show how this defect can be corrected. (c) Name the type of lens used to correct the defect. (2007)
Q.17 (a) What is meant by dispersion of white light? Describe the formation of rainbow in the sky with the help of a diagram.
(b) What is hypermetropia? Draw ray diagrams to show the image formation of an object by (i) hypermetropic eye (ii) correction made with a suitable lens for hypermetropic eye. (2008)
Q.18 (a) Give reasons for the following:
(i) Colour of the clear sky is blue.
(ii) The sun can be seen about two minutes
before actual sunrise.
(iii) We cannot see an object clearly if it is
placed very close to the eyes.
(b) What is presbyopia? Write two causes of this defect.
Q.1 A parallel beam of light falling on the eye gets focused on the retina because of refractions at:
(A) the cornea
(B) the crystalline lens
(C) the vitreous humor
(D) various surfaces in the eye
Q.2 The combination responsible for admitting different amounts of light into the eye is:
(A) ciliary muscles and crystalline lens (B) ciliary muscles and pupil
(C) iris and pupil
(D) rods and cones
Q.3 The muscles of the iris control the:
(A) focal length of the eye-lens
(B) opening of the pupil
(C) shape of the crystalline lens
(D) optic nerve
Q.4 When the eye is focused on an object very far away, the focal length of the eye-lens is:
(A) maximum
(B) minimum
(C) equal to that of the crystalline lens (D) half its maximum focal length
Q.5 Other names for myopia are:
(A) hyperopia and hypermetropia
(B) long-sightedness and hyperopia
(C) near-sightedness and presbyopia (D) near-sightedness and short-sightedness
Q.6 The inability among the elderly to see nearby objects clearly because of the weakening of: the ciliary muscles is called:
(A) far-sightedness
(B) near-sightedness
(C) presbyopia
(D) astigmatism
Q.7 When white light passes through a prism, it splits into its component colours. This phenomenon is called:
(A) spectrum (B) reflection
(C) refraction (D) dispersion
Q.8 The number of surfaces bounding a prism is:
(A) 3 (B) 4
(C) 5 (D) 6
Q.9 The wavelengths corresponding to violet, yellow and red lights are lv , ly and lr respectively.
Q.10 The focal length of eye lens is controlled by:
(A) Iris (B) Cornea
(C) Ciliary muscles (D) Optic nerve
Q.11 A white light falls on a glass prism, the least deviated colour is-
(A) Violet (B) Orange
(C) Red (D) Yellow
Q.12 Blue colour of sky is due to-
(A) dispersion of light
(B) scattering of light
(C) refraction of light
(D) reflection of light
Q.13 Rainbow is formed due to-
(A) reflection and dispersion of light through the water droplets
(B) total internal reflection, refraction and dispersion of light through the water droplets
(C) only dispersion of light
(D) only refraction of light
Q.14 Power of accommodation (max. variation in power of eye lens) of a normal eye is about:
(A) 1D (B) 2D
(C) 3D (D) 4D
Q.15 Dispersion of light by a prism is due to the change in-
(A) frequency of light
(B) speed of light
(C) scattering
(D) none of these
Q.16 Least distance of distinct vision of a
long-sighted man is 40 cm. He wish to reduce it to 25 cm by using a lens the focal length of the lens is-
(A) cm (B) cm
(C) +200 cm (D) -200 cm
Q.17 Which of the following colour has the least wavelength?
(A) Red (B) Orange
(C) Violet (D) Blue
Q.18 Convex lens of suitable focal length can correct-
(A) short sightedness
(B) long sightedness
(C) presbyopia
(D) astigmatism
Q.19 The focal length of human eye lens is
(with relaxed eye)-
(A) 2.5 cm (B) 25 cm
(C) 25 m (D) 2.5 m
Q.20 The middle colour in sunlight spectrum is:
(A) yellow (B) green [NTSE]
(C) blue (D) orange
Q.21 In which of the following cases will there be no dispersion when sunlight passes: [NTSE]
(A)
(B) 
(C) 
(D) 
Q.22 A ray of light falls on a prism having one silvered surface, at an incident angle of 45° as shown in figure. After refraction and reflection it retraces the path, then the refractive index of prism materials is (prism angle is 30°):
Q.23 A rainbow has circular shape because:[NTSE]
(A) the earth is spherical
(B) rain drops are spherical
(C) the sun is spherical
(D) none of these
Q.24 Find the value of Ðr' for the case shown in figure: [NTSE]
(A) sin–1 (0.5) (B) 75° –sin–1(0.5)
(C) 90° (D) 60°
Q.25 Dispersion of white light into its constituent colours occurs during: [NTSE]
(A) reflection at a plane mirror
(B) reflection at a concave mirror
(C) internal reflection inside a spherical drop of water
(D) refraction at the boundary of a transparent medium
Q.26 A ray of light passing through an equilateral triangular prism gets deviated at least by 30°. Then, the refractive index of the material of the prism must be: [NTSE]
Q.27 Our eye makes use of the property of:[NTSE]
(A) convex lens (B) concave lens
(C) cylindrical lens (D) none of these
Q.28 Most of the refraction of light takes place in the: [NTSE]
(A) iris (B) cornea
(C) pupil (D) retina
Q.29 The central circular aperture of _____ is called ________. [NTSE]
(A) iris, pupil (B) pupil, iris
(C) retina, iris (D) none of these
Q.30 When the light is very bright: [NTSE]
(A) the iris makes the pupil expand (B) the iris makes the pupil contract
(C) the iris and the pupil remain as they are (D) none of these
Q.31 Who discovered by his experiments with glass prisms that white light consists of seven colours? [NTSE]
(A) Newton (B) Faraday
(C) Maxwell (D) Young
Q.32 The light which refracts most while passing through a prism is: [NTSE]
(A) red (B) violet
(C) indigo (D) yellow
Q.33 Which of the following colours of light undergoes the least deviation while passing through a glass prism? [NTSE]
(A) red (B) blue
(C) yellow (D) green
Q.34 Which of the following colour of light undergoes the maximum deviation while passing through a glass prism? [NTSE]
(A) red (B) blue
(C) violet (D) green
Q.35 Which of the following sources of light is different from others? [NTSE]
(A) sunlight
(B) white light
(C) light from a bulb
(D) sodium light
Q.36 The wavelength of light is expressed in:[NTSE]
(A) metre (B) micron
(C) light year (D) angstrom
Q.37 A magnifying glass comprises a simple:[NTSE]
(A) convex lens (B) convex mirror
(C) concave lens (D) concave mirror
Q.38 The least distance of distinct vision for a normal person is: [NTSE]
(A) 1 m (B) 25 cm
(C) 25 m (D) none of these
Q.39 The power of a lens having a focal length of 1 cm is: [NTSE]
(A) 1 D (B) 10 D
(C) (D) 100 D
Q.40 A camera is an optical instrument which makes use of a: [NTSE]
(A) convex lens (B) concave lens
(C) cylindrical lens (D) none of these
Q.41 The inability of a lens to bring all the rays coming from a point object to focus at one single point is called: [NTSE]
(A) spherical aberration
(B) parallex
(C) optical illusion
(D) none of these
Q.42 The spherical aberration can be minimised by:
[NTSE]
(A) reducing the aperture of the lens (B) using specially made meniscus lens
(C) combination of lenses made of different glasses
(D) none of these
1. D 2. C 3. B 4. A 5. D
6. C 7. D 8. C 9. B 10. C
11. C 12. B 13. B 14. D
15. B 16. A 17. C 18. B
19. A 20. B
21. B 22. A 23. B 24. B
25. D 26. B 27. A 28. B
29. A 30. B 31. A 32. B
33. A 34. C 35. D 36. D
37. A 38. B 39. D 40. A
41. A 42. D
1. When does the total internal reflection take place :-
(A) Refraction from air into any denser medium
(B) Refraction of ray incident from rarer medium
(C) Ray incident from denser medium, with angle of refraction 90°
(D) Ray incident from denser medium with refractive index is [n > 1/(sin of angle of incidence)]
2. When the ray of light is incident from denser medium having refractive index 2, what should be the angle of incidence for the ray to go out :-
(A) Less than 30° (B) Less than 45° (C) Less than 60° (D) Less than 90°
3. A monochromatic beam of light passes from a denser medium into a rarer medium as a result :-
(A) Its velocity increase (B) Its velocity decrease
(C) Its frequency decrease (D) Its wavelength decreases
4. Immiscible transparent liquids A, B, C, D and E are placed in a rectangular container of glass with the liquids making laxers according to their densities. The refractive index of the liquids are shown in the adjoining diagram. The container is alluminated from the side and a small piece of glass having refractive index 1·61 is gently dropped into the liquid laxo. The glass piece as descends downwards will not be vissible in :-
(A) Liquid A and B only
(B) Liquid C only
(C) Liquid D and E only
(D) Liquid A, B, D and E
5. Sensitivity of eye is maximum for :-
(A) 4000 Å (B) 8000 Å (C) 5550 Å (D) 6000 Å
6. A bird in air looks at a fish vertically below it and inside water. x is the height of the bird above the surface of water and y is the depth of the fish below the surface of water. The distance of the fish as observed by the bird is : (Given m = refractive index of water w.r.t. air) :-
7. In the previous question, the distance of the bird as observed by the fish is :-
8. An object is placed between two parallel plane mirror. The number of images formed is
(A) four (B) one (C) two (D) infinite
9. An object is placed between two plane mirrors inclined at some angle to each other. If the number of images formed is 7 then the angle of inclination is
(A) 15° (B) 30° (C) 45° (D) 60°
10. Which of the following letters do not surface lateral inversion.
(A) HGA (B) HOX (C) VET (D) YUL
11. A clock hung on a wall has marks instead of numbers on its dial. On the opposite wall there is a mirror, and the image of the clock in the mirror if read, indicates the time as 8.20. What is the time in the clock-
(A) 3.40 (B) 4.40 (C) 5.20 (D) 4.20
12. If you want to see your full image, then minimum size of the mirror
(A) Should be of your height (B) Should be half of your height
(C) Should be twice of your height (D) Depends upon distance from the mirror
13. If an object is placed unsymmetrically between two plane mirrors, inclined at an angle of 72°, then the total number of images formed is-
(A) 5 (B) 4 (C) 2 (D) Infinite
14. At what angle must two plane mirrors be placed so that incident and resulting reflected rays are always parallel to each other
(A) 0° (B) 30° (C) 60° (D) 90°
15. Figure shows two plane mirrors parallel to each other and an object O placed between them. Then the distance of the first three images from the mirror M2 will be :(in cm)
(A) 5, 10, 15 (B) 5, 15, 30 (C) 5, 25, 35 (D) 5, 15, 25
16. If an object is placed 10 cm in front of a concave mirror of focal length 20 cm, the image will be :–
(A) diminished, upright, virtual (B) enlarged, upright, virtual
(C) diminished, inverted, real (D) enlarged, upright, real
17. The magnification m, the image position v and focal length f are related to one another by the relation -
18. The relation between magnification m, the object position u and focal length f of the mirror is
19. v1 is velocity of light in first medium, v2 is velocity of light in second medium, then refractive index of second medium with respect to first medium is
20. The ratio of the refractive index of red light to blue light in air is
(A) Less than unity
(B) Equal to unity
(C) Greater than unity (D) Less as well as gratert than unity depending upon the experimental arrangement
21. The refractive index of glass and water with respect to air are 3/2 and 4/3 respectively. The refractive index of glass with respect to water is
(A) 8/9 (B) 9/8 (C) 2 (D) 1/2
22. If iµj represents refractive index when a light ray goes from medium i to medium j, then the product is equal to
23. What is the basic reason for the shining of a diamond ?
(A) Reflection (B) Refraction (C) Dispersion of light (D) Total internal reflection
24. Total internal reflection of a ray of light is possible when the (ic = critical angle, i = angle of incidence)
(A) Ray goes from denser medium to rarer medium and i < ic
(B) Ray goes from denser medium to rarer medium and i > ic
(C) Ray goes from rarer medium to denser medium and i > ic
(D) Ray goes from rarer medium to denser medium and i < ic
25. A convex lens of focal length A and a concave lens of focal length B are placed in contact. The focal length of the combination is
26. Near and far points of a human eye are
(A) zero and 25 cm (B) 25 cm and 50 cm (C) 50 cm and 100 cm (D) 25 cm and infinite
27. The focal length of a concave mirror is f and the distance from the object to the principal focus is x. Then the ratio of the size of the image to the size of the object is-
28. Light travels through a glass plate of thickness t and having refractive index n. If c is the velocity of light in vacuum. the time taken by the light to travel this thickness of glass is :–
29. A ray of light passes through four transparent media with refractive indices m1, m2, m3, and m4 as shown in the figure. The surfaces of all media are parallel. If the emergent ray CD is parallel to the incident ray AB, we must have:
30. Which of the following is used in optical fibres?
(A) Total internal reflection (B) Scattering
(C) Diffraction (D) Refraction
31. Electromagnetic radiation of frequency n, wavelength l , travelling with velocity v in air, enters a glass slab of refractive index m . The frequency, wavelength and velocity of light in the glass slab will be respectively :–
32. A plane glass slab is kept over various coloured letters; the letter which appears least raised is
(A) blue (B) voilet (C) green (D) red
33. A convex lens of focal length f will form a magnified real image of an object if the object is placed
(A) anywhere beyond 2f (B) anywhere beyond f (C) between f and 2f (D) between lens and f
34. A convex lens is making full image of an object. if half of lens is covered by an opaque object, then
(A) half image is not seen (B) full image of same intensity is seen
(C) full image of decreased intensity is seen (D) half image of same intensity is seen
35. When a thin convex lens is put in contact with a thin concave lens of the same focal length, the
resultant combination has a focal length equal to
(A) f/2 (B) 2f (C) 0 (D) ¥
36. Focal length of a convex lens will be maximum for
(A) blue light (B) yellow light (C) green light (D) red light
37. A convex lens has a focal length f. It is cut into two parts along the dotted line as shown in the figure. The focal length of each part will be
(A)
(B) f
(C) f
(D) 2f
38. A convex lens is made up of three different materials as shown in the figure. For a point object placed on its axis, the number of images formed are
(A) 1
(B) 3
(C) 4
(D) 5
39. Myopia is the defect of vision due to which a person finds difficulty in seeing
(A) distant objects (B) near objects (C) objects at all distances (D) colours
40. Loss of the ability of eye to focus on near and far objects with advancing age is called
(A) Presbyopia (B) Astigmatism (C) Hypermetropia (D) Myopia
41. Astigmatism can be corrected by
(A) Bifocal lenses (B) Cylindrical lenses (C) Concave lenses (D) Planoconvex lenses
42. A normal eye is not able to see objects closer than 25 because
(A) The focal length of the eye is 25 cm
(B) The distance of the retina form the eye lens is 25 cm
(C) The eye is not able to decrease the distance between the eye lens and the retina beyond a limit
(D) The eye is not able to decrease the focal length beyond a limit
43. Myopia can be removed by using a lenses of
(A) concave lens (B) convex lens (C) cylindrical lens (D) by surgical removal
44. Two plane mirrors M1 and M2 each have length 1m and are separated by 1cm. A ray of light is incident on one end of mirror M1 at angle 45º. How many reflections the ray will have before going at from the other end
(A) 50 (B) 51 (C) 100 (D) 101
45. 'Mirage' is a phenomenon due to :–
(A) relfection of light (B) reflraction of light
(C) total internal reflection of light (D) diffraction of light
46. An observer can see through a pin-hole the top end of a thin rod of height h, placed as shown in the figure. The beaker height is 3h and its radius h. When the beaker is filled with a liquid up to a height 2h, he can see the lower end of the rod. Then the refractive index of the liquid is–
47. A ray of light is incident at the glass-water interface at an angle i. It emerges finally parallel to the surface of water as shown in fig. The value of µg would be –
48. When a ray of light enters a glass slab from air –
(A) Its wavelength decreases. (B) Its wavelength Increases.
(C) Its frequence Increases. (D) Neither wavelength nor frequence changes.
49. The distance between the object and the real image formed by a convex lens is d. if the magnification is m, the focal length of the lens is –
50. A parallel beam of light falls on a convex lens. The path of the rays is shown in fig. It follows that –
(A) µ1 > µ > µ2 (B) µ1 < µ < µ2 (C) µ1 = µ < µ2 (D) µ1 = µ > µ2
51. A person is looking at the image of his face in a mirror by holding it close to his face. The image is virtual. When he moves the mirror away from his face, the image is inverted. What type of mirror is he using?
(A) Plane mirror (B) Convex mirror (C) Concave mirror (D) None of these
52. Two objects A and B when placed in turn in front of a concave mirror of focal length 7.5 cm, give images of equal size. If A is three times the size of B and is placed 30 cm from the mirror, what is the distance of B from the mirror –
(A) 10 cm (B) 12.5 cm (C) 15 cm (D) 17.5 cm
53. A ray of light in medium of refractive index µ1 is partly reflected and refracted at the boundary of a medium of refractive index µ2 as shown fig. If ÐBOC = 90°. The value of angle i is given by –
(A) tan–1 (µ1/µ2) (B) tan–1 (µ2/µ1) (C) sin–1 (µ2/µ1) (D) cos–1 (µ1/µ2)
54. Two transparent media A and B separated by a plane boundary. The speed of light in medium A is 2.0 × 108 ms–1 and in medium B 2.5 × 108 m s–1. The critical angle for which a ray of light going from A to B it totally internally reflected is –
55. An air bubble in a glass slab (µ = 1.5) is 6 cm deep when viewed through one face and 4 cm deep when viewed through the opposite face. What is the thickness of the slab?
(A) 7.0 cm B) 7.5 cm (C) 15 cm (D) 10.5 cm
56. A point source of light S is placed at a distance L in front of the centre of a plane mirror PQ of width d hung vertically on a wall as shown in fig. A man walks in front of the mirror along a line parallel to the mirror at a distance 2L from it as shown. The greatest distance over which he can see the image of the light source in the mirror is –
(A) (B) d (C) 2d (D) 3d
57. Two plane mirros, each 1.6 m long, are held parallel and facing each other at a separation of cm. A ray of light is incident at the end of one mirror at an angle of incidence of 30°. The total number of reflections the ray suffers before emerging from the system of mirrors is –
(A) 10 (B) 12 (C) 14 (D) 16
58. Two plane mirrors A and B are aligned parallel to each other, as shown in Fig. A light ray is incident at an angle of 30° at a point just inside one end of A. The plane of incidence coincides with the plane of the figure. The maximum number of times the ray undergoes reflections (including the first one) before it emerges out is –
(A) 28 (B) 30 (C) 32 (D) 34
59. What is the relation between refractive indices µ, µ1 and µ2 if the behaviour of light rays is as shown in fig.
(A) µ > µ2 > µ1 (B) µ < µ2 < µ1 (C) µ < µ2 : µ = µ1 (D) µ2 < µ1 : µ = µ2
60. A lens of power +2.0D is placed in contact with another lens of power –1.0D, the combination will behave like :-
(A) A converging lens of focal length 100 cm
(B) A diverging lens of focal length 100 cm
(C) A converging lens of focal length 50 cm
(D) A diverging lens of focal length 50 cm
61. Which of the following statements is/are correct?
(A) The laws of reflection of light hold for plane as well as curved reflecting surfaces.
(B) The size of a virtual image can be measured by receiving it on a screen.
(C) A dentist uses a convex mirror to examine a small cavity.
(D) The focal length of a spherical mirror is half the radius of curvature for all rays.
62. Choose the correct statement(s) from the following:
(A) To a fish under water looking obliquely at a man standing on the bank of lake, the man looks taller than his actual height.
(B) The apparent depth of a tank of water is more for oblique viewing than for normal viewing.
(C) The focal length of a concave mirror will not change if it is immersed in water.
(D) In no situation will a converging lens behave like a diverging lens.
63. An air bubble under water shines brightly because of the phenomenon of –
(A) Dispersion (B) Interference
(C) Diffraction (D) Total internal reflection
64. The distance v of the real image formed by a convex lens is measured for various object distances u.
A graph is plotted between v and u. Which one of the graphs shown in fig. is approximately correct?
(A) 
(B) 
(C) 
(D) 
65. If a graph is plotted between 1/v and 1/u, which one of the graphs shown in fig. approximately correct?
(A) 
(B) 
(C) 
(D) 
66. Which one of the following statements is correct for spherical mirrors ?
(A) A concave mirror forms only virtual images for any position of the object.
(B) A convex mirror forms only virtual images for any position of the object.
(C) A concave mirror forms only a virtual diminished image of an object placed between its pole and the focus.
(D) A convex mirror forms a virtual magnified image of an object placed between its pole and the focus.
67. A concave mirror produces a real image twice the size of the object when place at a distance of 22.5 cm from it. At what distance from the mirror should the object be placed so that the image becomes three times the size of the object?
(A) 20 cm
(B) 25 cm
(C) 30 cm
(D) 40 cm
68. The distance of an object from the focus of a concave mirror of focal length f is x and the distance of the real image from the focus is y. Then
(A) 
(B) 
(C) xy = f2
(D) none of these
69. The distance of an object from the focus of a convex mirror of focal length f is x and the distance of the image from the focus is y. Then
(A) 
(B)
(C) xy =f2
(D) none of these