Solution of Chapter 6. The Human Eye and The Colourful World (Lakhmir Singh & Manjit Kaur - Physics Book)

What kind of lens is present in the human eye?

Name two parts of the eye which refract light rays (or bend light rays).

Name the part of the eye:

(a) Which controls the amount of light entering the eye.

(b) on which the image is formed.

(c) which changes the focal length of eye.

What is the name of:

(a) the curved, transparent front surface of the eye ?

(b) the light-sensitive layer in the eye?

Where is the image formed in a human eye?

What is the function of the lens in the human eye?

What job does the pupil of the eye do?

How does the eye adjust to take account of an increase in brightness?

Name that part of the eye which is equivalent to the photographic film in a camera.

Name the part of the retina which is insensitive to light.

Which part of the eye contains cells which are sensitive to light?

Name two types of cells in the retina of an eye which respond to light.

Out of rods and cones in the retina of your eye:

(a) which detect color?

(b) which work in dim light?

State whether the following statement is true or false: The image formed on our retina is upside-down

What is the principal function of the eye-lens?

Where does the greatest degree of refraction of light occur in the eye?

What changes the shape of lens in the eye?

What do the ciliary muscles do when you are focusing on a nearby object?

What is the least distance of distinct vision for a normal human eye ?

What is the:

(a) far point of a normal human eye?

(b) near point of a normal human eye?

What is the range of vision of a normal human eye?

Name the part of our eyes which helps us to focus near and distant objects in quick succession.

Define the term "power of accommodation" of human eye.

Give the scientific names of the following parts of the eye:

(a) carries signals from an eye to the brain.

(b) muscles which change the shape of the eye-lens.

(c) a hole in the middle of the iris.

(d) a clear window at the front of the eye.

(e) changes shape to focus a picture on the retina.

Fill in the following blanks with suitable words:

(a) Most of the refraction of light rays entering the eye occurs at the outer surface of the _______

(b) The part of eye sensitive to light is_______

(c) The part of eye which alters the size of the pupil is_______

(d) When light is dim, the pupil becomes_______

(e) The iris controls the amount of_______entering the eye.

(f) The ciliary muscles control the shape of the _______

(g) To bring light from a distant object to a focus on the retina of the eye, the convex eye-lens needs to be made_______

(h) To bring light from a near object to a focus on the retina of the eye, the convex eye-lens needs to be made_______

Why is a normal eye not able to see clearly the objects placed closer than 25 cm?

What changes take place in the shape of eye-lens : (a) when the eye is focused on a near object?

(b) when the eye is focused on a distant object ?

The eyes of a person are focused (i) on a nearby object, and (ii) on a distant object, turn by turn. In which case:

(a) the focal length of eye-lens will be the maximum ?

(b) the converging power of eye-lens will be the maximum?

What change is made in the eye to enable it to focus on objects situated at different distances ? Illustrate your answer with the help of diagrams.

How is the amount of light entering the eye controlled?

What happens to the eye when you enter a darkened cinema hall from bright sunshine? Give reason for your answer.

Why does it take some time to see objects in a dim room when you enter the room from bright sunshine outside?

A person walking in a dark corridor enters into a brightly lit room:

(a) State the effect on the pupil of the eye.

(b) How does this affect the amount of light entering the eye ?

Ciliary muscles of human eye can contract or relax. How does it help in the normal functioning of the eye ?

Describe and explain, how a normal eye can see objects lying at various distances clearly.

There are two types of light-sensitive cells in the human eye:

(a) Where are they found ?

(b) What is each type called?

(c) To what is each type of cell sensitive?

What are rods and cones in the retina of an eye? Why is our night vision relatively poor compared to the night vision of an owl?

How does the convex eye-lens differ from the ordinary convex lens made of glass?

List, in order, the parts of the eye through which light passes to reach the retina.

What happens to the size of pupil of our eye

(i) in dim light (ii) in bright light ?

Name the cells on the retina of an eye which are sensitive to

(i) bright light (ii) dim light (iii) sensation

Draw a simple diagram of the human eye and label clearly the cornea, iris, pupil, ciliary muscles, eye �

lens, retina, optic nerve and blind spot.

Describe the working of the human eye with the help of the above diagram.

How does the eye adjust itself to deal with light of varying intensity?

Explain the functions of the following parts of the eye :

(a) cornea (b) iris (c) pupil (d) ciliary muscles (e) eye-lens (f) retina (g) optic nerve

If you walk from a dark room into sunlight and back again into dark room, how would your pupils alter in size? What makes this happen?

Explain why, we cannot see our seats first when we enter a darkened cinema hall from bright light but gradually they become visible.

The human eye forms the image of an object at its :

The change in focal length of an eye-lens is caused by the action of the:

The least distance of distinct vision for a young adult with normal vision is about :

Refraction of light in the eye occurs at:

To focus the image of a nearby object on the retina of an eye:

The term "accommodation" as applied to the eye, refers to its ability to:

Which of the following controls the amount of light entering the eye ?

The human eye possesses the power of accommodation. This is the power to:

How does the eye change in order to focus on near or distant objects ?

Which of the following changes occur when you walk out of bright sunshine into a poorly lit room ?

The size of the pupil of the eye is adjusted by:

The descriptions of five kinds of images are given below:

(a) diminished and virtual (b) enlarged and real

(c) enlarged and erect (d) real and inverted

(e) virtual and the same size

Which one of these describes the image formed:

(i) on the retina of the eye?

(ii) by a magnifying glass?

(iii) by a convex driving mirror on a car?

(iv) by a plane mirror?

(v) on the screen of a slide projector?

What shape are your eye-lenses:

(a) when you look at your hand ?

(b) when you look at a distant tree ?

suggest how your irises help to protect' the retinas of your eyes from damage by bright light.

Which parts of the eye cause rays of light to converge on the retina ?

Which part causes the greatest convergence ?

Which part brings the image into sharp focus on the retina? How does it do this?

An object is moved closer to an eye. What changes must take place in the eye in order to keep the image in Sharp focus?

Why does the eye-lens not have to do all the work of converging incoming light rays?

Explain why, when it is getting dark at night, it is impossible to make out the color of cars on the road.

Nocturnal animals (animals which sleep during the day and come out at night) tend to have wide pupils and lot of rods in their retinas. Suggest reasons for this.

Name one of the common defects of vision and the type of lens used to remove it.

Name the defect of vision in a person;

(a) whose near point is more than 25 cm away.

(b) whose far point is less than infinity

Which defect of vision can be rectified:

(a) by using a concave lens ?

(b) by using a convex lens?

What type of lens is used to correct

(a) hypermetropia

(b) myopia?

What is the other name for

(a) myopia

(b) hypermetropia?

What is the scientific name of

(a) short-sightedness, and (b) long-sightedness?

What kind of lens is used to correct (a) short-sightedness (b) long-sightedness?

State whether the following statement is true or false : Short-sightedness can be cured by using a concave lens.

Name the defect of vision in which the eye-lens loses its power of accommodation due to old age.

Name the defect of vision which makes the eye-lens cloudy resulting in blurred vision.

What is the other name of old age hypermetropia?

Name any two defects of vision which can be corrected by using spectacles.

Name one defect of vision (or eye) which cannot be corrected by any type of spectacle lenses.

Name the body part with which the terms myopia and hypermetropia are connected.

What is the far point of a person suffering from myopia (or short-sightedness)?

Where is the near point of a person suffering from hypermetropia (or long-sightedness)?

Your friend can read a book perfectly well but cannot read the writing on blackboard unless she sits on the front row in class.

(a) Is she short-sighted or long-sighted?

(b) What type of lenses-converging or diverging-would an optician prescribe for her?

A man can read the number of a distant bus clearly but he finds difficulty in reading a book.

(a) From which defect of the eye is he suffering?

(b) What type of spectacle lens should he use to correct the defect?

A student sitting in the last row of the class-room is not able to read clearly the writing on the blackboard.

(a) Name the type of defect he is suffering from.

(b) How can this defect by corrected?

Complete the following sentences:

(a) A short-sighted person cannot see _______ objects clearly. Short-sightedness can be corrected by using

_______ lenses.

(b) A long-sighted person cannot see _______ objects clearly. Long-sightedness can be corrected by using

_______ lenses.

What are the two most common defects of vision (or defects of eye)? How are they corrected?

Differentiate between myopia and hypermetropia. What type of spectacles should be worn by a person having the defects of myopia as well as hypermetropia? How does it help ?

Name the defect of vision which can be corrected by a converging lens. Show clearly by a ray diagram how the lens corrects the defect.

Name the defect of vision which can be corrected by a diverging lens. Show clearly by a ray diagram how the lens corrects the defect.

Explain with the help of labelled ray diagram, the defect of vision called myopia and how it is corrected by a lens.

Explain with the help of labelled ray-diagram, the defect of vision called hypermetropia, and how it is corrected by a lens.

A person suffering from the eye-defect myopia (short-sightedness) can see clearly only up to a distance of 2 metres. What is the nature and power of lens required to rectify this defect?

The near-point of a person suffering from hypermetropia is at 50 cm from his eye. What is the nature and power of the lens needed to correct this defect? (Assume that the near-point of the normal eye is 25 cm).

A person needs a lens of power, - 5.5 dioptres for correcting his distant vision. For correcting his near vision, he needs a lens of power, +1.5 dioptres. What is the focal length of the lens required for correcting

(i) distant vision, and (ii) near vision?

What is presbyopia? Write two causes of this defect. Name the type of lens which can be used to correct presbyopia.

When is a person said to have developed cataract in his eye ? How is the vision of a person having cataract restored?

Fill in the following blanks with suitable words:

A person is short-sighted if his eyeball is too ______ Spectacles with a ______ lens are needed. A person is long-sighted if his eyeball is too ______ Spectacles with a ______ lens are needed. These focus light rays exactly on to the ______

What is short-sightedness ? State the two causes of short-sightedness (or myopia). With the help of ray diagrams, show:

(i) the eye-defect short-sightedness.

(ii) correction of short-sightedness by using a lens.

A person having short-sight cannot see objects clearly beyond a distance of 1.5 m. What would be the nature and power of the corrective lens to restore proper vision?

What is long-sightedness? State the two causes of long-sightedness (or hypermetropia). With the help of ray diagrams, show:

(i) the eye-defect long-sightedness.

(ii) correction of long-sightedness by using a lens.

An eye has a near point distance of 0.75 m. What sort of lens in spectacles would be needed to reduce the near point distance to 0.25 m? Also calculate the power of lens required. Is this eye long-sighted or short � sighted?

An eye has a far point of 2 m. What type of lens in spectacles would be needed to increase the far point to infinity? Also calculate the power of lens required. Is this eye long-sighted or short-sighted?

The human eye can focus objects at different distances by adjusting the focal length of the eye-lens. This is due to:

The defect of vision which cannot be corrected by using spectacles is :

A person cannot see the distant objects clearly (though he can see the nearby objects clearly). He is suffering from the defect of vision called :

Though a woman can see the distant objects clearly, she cannot see the nearby objects clearly. She is suffering from the defect of vision called:

A young man has to hold a book at arm's length to be able to read it clearly. The defect of vision is:

After testing the eyes of a child, the optician has prescribed the following lenses for his spectacles:

Left eye : + 2.00 D Right eye : + 2.25 D

The child is suffering from the defect of vision called :

A person got his eyes tested. The optician's prescription for the spectacles reads:

Left eye : - 3.00 D Right eye : - 3.50 D

The person is having a defect of vision called :

A student sitting on the last bench in the class cannot read the writing on the blackboard clearly but he can read the book lying on his desk clearly. Which of the following statement is correct about the student?

A man driving a car can read a distant road sign clearly but finds difficulty in reading the odometer on the dashboard of the car. Which of the following statement is correct about this man?

The defect of vision in which the eye-lens of a person gets progressively cloudy resulting in blurred vision is called:

A person cannot see distant objects clearly. His vision can be corrected by using the spectacles containing:

A person finds difficulty in seeing nearby objects clearly. His vision can be corrected by using spectacles containing :

In a certain murder investigation, it was important to discover whether the victim was long-sighted or short-sighted. How could a detective decide by examining his spectacles?

The picture given here shows a person wearing 'half-moon' spectacles. What sort of eye-defect do you think he has ? Why are these particular spectacles useful to him?

A short-sighted person has a near point of 15 cm and a far point of 40 cm.

(a) Can he see clearly an object at a distance of:

(i) 5 cm ? (ii) 25 cm ? (iii) 50 cm ?

(b) To see dearly an object at infinity, what kind of spectacle lenses does he need ?

The near point of a long-sighted person is 50 cm from the eye.

(a) Can she see dearly an object at:

(i) a distance of 20 cm ? (ii) at infinity ?

(b) To read a book held at a distance of 25 cm, will she need converging or diverging spectacle lenses?

A person can read a book dearly only if he holds it at an arm's length from him. Name the defect of vision:

(a) if the person is an old man

(b) if the person is a young man

How much is our field of view:

(a) with one eye open?

(b) with both eyes open?

Which of the following have a wider field of view?

(a) Animals having two eyes on the opposite sides of their head.

(b) Animals having two eyes at the front of their head.

Out of animals of prey and predators, which have their eyes:

(i) at the front of their head?

(iii) on the opposite sides of their head?

State whether the following statement is true or false: Rabbit has eyes which look sideways.

Fill in the following blanks with suitable words:

(a) Having two eyes gives a ______ field of view.

(b) Having two eyes enables us to judge ______ more accurately.

What are the advantages of having two eyes instead of just one?

Explain clearly why, a person who has lost the sight of one eye is at a disadvantage compared with the normal person who has two good eyes.

Name two animals having eyes:

(a) on the sides of the head.

(b) at the front of the head.

Among animals, the predators (like lions) have their eyes facing forward at the front of their heads, whereas the animals of prey (like rabbit) usually have eyes at the sides of their head. Why is this so?

Five persons A, B, C, D and E have diabetes, leukaemia, asthma, meningitis and hepatitis, respectively.

(a) Which of these persons can donate eyes?

(b) Which of these persons cannot donate eyes?

The animal which does not have eyes that look sideways is:

With both eyes open, a person's field of view is about:

Having two eyes gives a person:

The animals of prey have:

The animals called predators have:

As light rays pass from air into a glass prism, are they refracted towards or away from the normal?

As light rays emerge from a glass prism into air, they got refracted towards or away from the normal ?

Name a natural phenomenon which is caused by the dispersion of sunlight in the sky.

What information do we get about sunlight from the formation of a rainbow?

What did Newton demonstrate by his experiments with the prism?

What colours make up white light?

Give the meaning of the term VIBGYOR. With which phenomenon is it connected?

In the formation of spectrum of white light by a prism :

(i) which colour is deviated least?

(ii) which colour is deviated most?

What colours lie on the two sides of the 'green colour' in the spectrum of white light?

Name the scientist who discovered that sunlight consists of seven colours.

What is the order of colours in a rainbow, from the outside to the inside?

Which colour of the spectrum has

(a) longest wavelength, and

(b) shortest wavelength ?

Which light has the longer wavelength : red light or blue light ?

Which colour of light has the shorter wavelength - red or violet ?

Fill in the blanks with suitable words:

(a) When a ray of light enters a prism, it bends.................the normal; as it leaves the prism, it bends ............ the normal.

(b) White light is composed of .............colours. The colour of white light deviated through the largest angle by a prism is..............

A ray of white light breaks up into its components while passing through a glass prism.

Draw a ray diagram to show the path of rays.

Mark the least deviated colour in your diagram.

Why do different coloured rays deviate differently in a prism?

What happens when a ray of ordinary light is passed through a triangular glass prism?

What will happen if another similar glass prism is placed upside down behind the first prism?

When a beam of white light is passed through a prism, it splits to form lights of seven colours. Is it possible to recombine the lights of seven colours to obtain the white light again? Explain your answer.

What is spectrum? What is the name of glass shape used to produce a spectrum?

How many colours are there in a full spectrum of white light? Write the various colours of spectrum in the order, starting with red.

What is meant by dispersion of white light? Describe the formation of rainbow in the sky with the help of a diagram.

In the figure given alongside, a narrow beam of white light is shown to pass through a triangular glass prism. After passing through the prism, it produces a spectrum YX on the screen.

(a) State the colour seen (i) at X, and (ii) at Y.

(b) Why do different colours of white light bend through different angles with respect to the incident beam of light?

Draw a diagram to show how white light can be dispersed into a spectrum by using a glass prism. Mark the various colours of the spectrum.

Make two diagrams to explain refraction and dispersion.

Describe how you could demonstrate that white light is composed of a number of colors.

How could you show that the colours of the spectrum combine to give white light ?

Which is refracted most by a prism : red light or violet light ? Explain why?

Draw a diagram to show the refraction of light through a glass prism. On this diagram, mark (i) incident ray (ii) emergent ray, and (iii) angle of deviation.

What is a rainbow? What are the two conditions necessary for the formation of a rainbow in the sky?

What acts as tiny prisms in the formation of a rainbow?

Name the process which is involved in the formation of a rainbow.

What are the seven colours seen in a rainbow?

A beam of white light is shone onto a glass prism. The light cannot be:

A beam of white light falls on a glass prism. The colour of light which undergoes the least bending on passing through the glass prism is :

The colour of white light which suffers the maximum bending (or maximum refraction) on passing through a glass prism is :

Which of the following colour of white light is least deviated by the prism?

The colour of white light which is deviated the maximum on passing through the glass prism is:

The splitting up of white light into seven colours on passing through a glass prism is called :

Which of the following coloured light has the least speed in glass prism ?

The coloured light having the maximum speed in glass prism is :

Which of the following colour of white light has the least wavelength?

Out of the following, the colour of light having the maximum wavelength is:

Why do you not see a spectrum of colours when light passes through a flat pane of glass ?

Name some everyday objects:

(a) which reflect all the colors in sunlight

(b) which absorb all the colors in sunlight

Where in nature can you find evidence that white sunlight may be made of different colours?

Name the phenomenon which causes the twinkling of stars.

Name two effects produced by the atmospheric refraction.

Which phenomenon makes us see the sun:

(a) a few minutes before actual sunrise?

(b) a few minutes after actual sunset?

Atmospheric refraction causes advance sunrise and delayed sunset. By how much time is:

(a) sunrise advanced?

(b) sunset delayed?

State whether the following statement is true or false:

The planets twinkle at night due to atmospheric refraction of light.

Name the phenomenon due to which the stars seem higher in the sky than they actually are.

Fill in the following blanks with suitable words:

We can see the sun about.............minutes before the actual sunrise and about.............minutes after the actual sunset because of atmospheric...............

Why do stars seem higher than they actually are? illustrate your answer with the help of a diagram.

Explain why, the sun can be seen about two minutes before actual sunrise. Draw a diagram to illustrate your answer.

Explain why, if we look at objects through the hot air over a fire, the objects appear to be moving (or shaking) slightly.

What is atmospheric refraction? What causes atmospheric refraction?

Why do stars twinkle on a clear night ?

Explain why, the planets do not twinkle at night.

The twinkling of stars is due to atmospheric:

The atmospheric refraction of light causes the twinkling of:

The stars appear higher in the sky than they actually are, due to:

The stars twinkle but the planets do not twinkle at night because:

As light from a far off star comes down towards the earth:

We can see the sun before the actual sunrise by about:

Due to atmospheric refraction of sunlight, the time from sunrise to sunset is lengthened by about:

The day is longer on the earth by about 4 minutes because:

We know that light refracts (or bends) when it goes from one medium to another. Now, the atmosphere contains only air. Then how does light get refracted on passing through only air in the atmosphere?

By how much time the day would have been shorter if the earth had no atmosphere?

A student claims that because of atmospheric refraction, the sun can be seen after it has set, and the day is, therefore, longer than if the earth had no atmosphere.

(a) What does the student mean by saying that the sun can be seen after it has set?

(b) Do you think that the students' conclusion is correct?

What is the colour of the sunlight:

(a) scattered by the dust particles in the atmosphere?

(b) scattered by the air molecules in the atmosphere?

Which of the two is scattered more easily: light of shorter wavelengths or light of longer wavelengths?

State whether the following statements are true or false:

(a) The scattering away of red light makes the sky appear blue during the day time.

(b) The scattering away of blue light makes the sun appear red at sunset.

What colour does the sky appear to an astronaut?

Which effect is illustrated by the observation that when a beam of sunlight enters a dusty room, then its path becomes visible to us.

State two effects produced by the scattering of light by the atmosphere.

What is tyndall effect? Explain with an example.

What happens when a beam of sunlight enters a dusty room through a window ? Explain your answer.

Why does the sky appear blue on a clear day ?

Why does the sky appear dark (or black) to an astronaut instead of blue?

Why does the sun appear red at sunrise ?

Why does the sun appear red at sunset ?

Why are the 'danger signal' lights red in colour?

Draw a neat and labelled diagram of the experimental set up for observing the scattering of light in a colloidal solution of sulphur to show how the sky appears blue, and the sun appears red at sunrise and sunset.

Out of blue light and red light, which one is scattered more easily?

Which component of sunlight is scattered away when the sun appears red at sunrise or sunset?

What causes the scattering of blue component of sunlight in the atmosphere?

The blue colour of sky is due to:

The red colour of the sun at the time of sunrise and sunset is because:

Which of the following is not caused by the atmospheric refraction of light?

The sky appears blue because some of the blue component of sunlight is scattered by:

Sunset is red because at that time the light coming from the sun has to travel:

In an experiment to study the scattering of light by passing a beam of white light through a colloidal solution of sulphur in a transparent glass tank :

(a) Which colour is observed from the front of the glass tank? Does this colour correspond to the colour of sky on a clear day or the colour of sky around the sun at sunset ?

(b) Which colour is observed from the sides of the glass tank? Does this colour correspond to the colour of sky on a clear day or the colour of sky around the sun at sunset ?

Explain why, when the sun is overhead at noon, it appears white, but when the same sun is near the horizon at sunset, it appears red.

Complete the following statements:

When the sun is setting, the light from it has to travel a ...............thickness of the earth's atmosphere and only ........... wavelength ........... light is able to reach us. Sunset is therefore .......