CBSE PHYSICS: 10th Human eyes and Colorful World

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22 October 2013

X Board Question Ch: Human Eye and Colourful World

Guess Paper for Board exam 2014

Q. (a) List the factors on which scattering of light depends. (b) What is Tyndals, effect ?

Q. A student sitting on the last bench in a class room cannot read the black board clearly.

(i) Name the kind of defect of vision the student is suffering from.

(ii) Name the type of spherical lens he has to use to correct this defect.

(iii) State two possible reasons for this defect of vision.

Q. Why do stars appear to twinkle while the planets do not ? Explain with the help of diagram.

Q. Explain with the help of diagram why the sun is visible to us two minutes before the actual sun-rise and two minutes after the sunset.

Q. (a) What is meant by power of accommodation of eye ? A person with a defective vision cannot see objects beyond 1.2 m distinctly. What should be the type of the corrective lens used to restore proper vision ? Draw a diagram of thus corrected eye. (b) A person having presbyopia uses a bifocal lens to restore proper vision. Which part of the this lens is convex and which part is concave ?

Q. Name the part responsible for the power of accommodation of the human eye.

Q. What is meant by least distance of distinct vision ? How does this vary between the very young and old people ?

Q. Explain why the colour of the clear sky is blue.

Q. State the cause of dispersion, when white light enters a glass prism. Explain with a diagram

Q. What is a rainbow ? When and how is it formed ?

Q. Explain the cause of the red colour of the Sun at Sunrise and Sunset.

Q. List two causes leading to myopia of the eye. Draw ray diagrams to show the image formation in case of defective eye and corrected eye.

Q. We can see the sun for few minutes even after it has actually set. Why ?

Q. A student has difficulty in reading the blackboard while sitting in the last row. What could be the defect of vision the student is suffering from ? What are the causes for this disorder ?

Q. What is meant by power of accommodation of eye ? The minimum power of eye lens is 40D. If the far point of normal eye is infinity find the size of eye ball.

Q. The sky appears dark to the passengers flying at very high attitudes. Why ?

Q. A child has difficulty in reading the blackboard while sitting on the last bench in a class room. What could be the defect the child is suffering from ? List two main causes of this defect.

Q. State the nature of the image formed at the retina of human eye.

Q. (a) What is the near point of the human eye with normal vision ? (b) Why is a normal eye not able to see clearly the objects placed closer than the near point ?

Q. The sun appears oval (or flattened) at sunrise and sunset, but appears circular at noon. Explain, why ?

Q. A student has difficulty in reading the black board while sitting in the last row

What could be the defect the student is suffering from ? How can it be corrected ? Draw the ray diagrams for (a) defective eye (b) its correction.

Q. State the range of the human eye with a normal vision

Q. Q. “Stars seem higher than they actually are” Explain, why?

Q. What is meant by the power of accommodation of the eye? State the role of ciliary muscles in achieving it.

Q. (a) What is long sightedness? List its causes. (b) How can it be corrected? Draw the ray diagram for its correction.

Q. Define absolute refractive index of a medium. Light enters from air to water having refractive index 4/3. Find the speed of light in water. The speed of light in vacuum is 3x10⁸ m/s.

Q. With the help of a diagram, explain the formation of a rainbow in the sky.

Q. (i) What is meant by “least distance of distinct vision” ? (ii) How does iris controls the size of the pupil in bright light and dim light ?

Q. A person can see distant sign boards clearly but cannot read clearly a book which is at 25 cm from his eye. Identify the defect. Draw a labelled ray diagram to illustrate how this defect can be corrected.

Q. A person needs a lens of power – 2.5 dioptres for correcting his vision. Name the defect of vision he is suffering from. Which lens will he be using for the correction ? Also find the focal length of the lens.

Useful study link from: http://jsuniltutorial.weebly.com/the-human-eye-and-the-colourful-world.html

10th Human eye and Atmospheric refraction Notes

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Human eyes and Colorful world (commit to memory)

X Solved NCERT Questions: The Human Eye and the Colorful World

Human Eyes and Colorful world Guess Question solved X (10th)

X CBSE PHYSICS Human Eyes Questions for Practice

CBSE Class 10 Physics The Humane Eyes Study Notes

CBSE X Question Bank Human eyes and Colorful World

THE HUMAN EYE AND THE COLOURFUL WORLD E-Study Notes

Solved questions for Chapter: The Human Eye and the Colorful World View

X (10th) Human eyes and Colorful World View

CBSE Physics Chapter 11 Human Eye and Colorful World class View

24 December 2012

CBSE Chapter 11 Human Eye and Colorful World Solved Worksheet

Gist of Lesson for Quick Revision (By JSUNIL)

1. An eye is the most important organ of the human body. It is associated with vision and acts as a vital optical instrument.

2. An eye is spherical in shape of about 2.3 cm diameter and is covered externally by a hard thick and opaque layer called Sclerotica. The outermost layer of the eye is sclerotic that prtects and holds the eye.

3. Cornea is transparent partbulging out of eye and allows the light to enter in the eye. Cornea is also known as the window or aperture of the eye.

4. Iris is a circular diaphragm having a hole in its centre .this hole is called pupil

5. Iris has muscles and coloured pigments that provide different colour y eyes

6. Iris controls the amount of light entering the eye through the pupil.
7. The pupil becomes small when bright light falls on the eye. However, it becomes wide when there is dim light.

03 December 2012

X(10th) Human eyes and Colorful World

Gist of Lesson - Commit to remember.

1. The human eye is like a camera. Its lens system forms an image on a light sensitive screen called the retina.

2. The eye ball is approx. spherical in shape with a diameter of 2.3cm.

3. The human eye has the following parts:-

(a) Cornea:-The transparent spherical membrane covering the front of the eye.

(b) Iris:-The coloured diaphragm between the cornea and lens.

(c) Pupil:-The small hole in the iris.

(d) Eye lens:-Its is a transparent lens made of jelly like material.

(e) Ciliary muscles:-These muscles hold the lens in position.

(f) Retina:-The back surface of the eye.

(g) Blind spot:-The point at which the optic nerve leaves the eye. An image formed at
this point is not sent to the brain.

(h) Aqueous humour:-A clear liquid region between the cornea and the lens.

(i) Vitreous humour:-The space between eye lens and retina is is filled with another
liquid called Vitreous humour.

4. In the eye, the image is formed on the retina by successive refraction at the cornea,
the aqueous humour, the lens and the vitreous humour. Electrical signals then travel
along the optic nerve to the brain to be interpreted.

In good light, the yellow spot is most sensitive due to presence of large
number of rods and cones to detail and the image automatically formed there.

5. Accommodation:-The ability of the eye to focus both near and distant objects, by
adjusting the focal length, is called the accommodation of the eye

or,

The ability of the ciliary muscles to change the focal length of the eye lens is called
accommodation.

When we see distant objects Ciliary muscles get relax. This decreases the
curvature of the eye lens and the lens becomes thin to increase focal length.

When we see nearby objects ciliary muscles get contract. This increases the
curvature of the eye lens and the lens becomes thicker to decrease focal length.

6. Defects of the eye:- Although the eye is one of the most remarkable organs in the
body, it may have several abnormalities, which can often be corrected with eye glasses,
contact lenses, or surgery.

The various defects from which an eye can suffer are (i) Hypermetropia or
long shortsightedness. (ii) Myopia or short sightedness and (iii) *Astigmatism. (iv)
Presbyopia.

7. Hyper metropia : A person suffering from this defect can see distant objects clearly
but cannot see nearby objects clearly. In this defect, the near point lies further away
from 25cm.

Hyper metropia (far sightedness)- the image of nearby objects is focused beyond the retina) is corrected by using a convex lens of suitable power. The eye losses its power of accommodation at old age.

8. Hyper metropia is due to the following reasons:-

(i) Either the hyperopic eye ball is too short or

(ii) The Ciliary muscle is unable to change the shape of the lens enough to properly focus the image that is the focal length of the eye lens increases.

9. Myopia or short sightedness or near sightedness:-A person suffering from myopia or short sightedness can see nearby objects clearly but cannot see the faraway objects clearly.

Myopia (shortsightedness-the image of distant objects is focused before the retina) is
corrected by using a concave lens of suitable power.

10. Presbyopia is the defect of human eye due to which an old person cannot read and write comfortably. That is why presbyopia is also called old sight.

11. Astigmatism:- The defect by which the person is notable to differentiate horizontal and vertical position, is called astigmatism. It is a defect in which a person cannot see in all directions equally well. It can be rectified by using cylindrical lenses.

Astigmatism is an eye condition with blurred vision as its main symptom. The front surface of the eye (cornea) of a person with astigmatism is not curved properly – the curve is irregular - usually one half is flatter than the other - sometimes one area is steeper than it should be.

When light rays enter the eye they do not focus correctly on the retina, resulting in a blurred image. Astigmatism may also be caused by an irregularly shaped lens, which is located behind the cornea.
Astigmatism is a type of refractive error. A refractive error means that the shape of the eye does not bend light properly, resulting in a blurred image. Light has to be bent (refracted) by the lens and the cornea correctly before it reaches the retina in order to see things clearly.

The two most common types of astigmatism are:

(a) Corneal astigmatism - the cornea has an irregular shape
(b) Lenticular astigmatism - the lens has an irregular shape

In astigmatism, images focus in front of and beyond the retina, causing both close and distant objects to appear blurry (see below figure).

11. As our two eyes are separated by a few centimeters, each eye observes a
slightly different image. Our brain combines the two views into one and we get to know
how close or far away the things seen are.

12. The smallest distance, at which the eye can see objects clearly without strain, is called the near point of the eye or the least distance distinct vision. For a young adult with normal vision, it is about 25cm.

13. The distance between far point and near point of the eye is called range of vision
of the eye.

14. Spectrum is a band of distinct colors we obtain when white light is split by a prism.

15. Causes of dispersion:- Every colour has its own characteristic wave length or
frequency. Different colors move with same speed in air/vacuum. But their speeds in
refracting media like glass are different. Therefore, refractive index of the medium for different colors is different.

As a result, different colors undergo different deviations on passing through the prism. Hence, different colors emerge from the prism along different directions.

16. In any medium other than air/vacuum red light travels the fastest and violet
light travels the slowest.

17. When we pass white light through two identical prisms held side by side with their
refracting edges in opposite direction; the first prism disperses white light into
seven colors and the second prism recombines the seven colors into white light. Thus
light emerging from second prism is white.

18. A rainbow is formed due to dispersion of light by tiny droplets of water which act
as prisms.

19. Scattering of light causes the blue colour of the sky and the reddening of the sun
at sunrise and sunset.

20.We can see the sun about 2 minutes before the actual sunrise, and about 2 minutes after the actual sunset because of atmospheric refraction.

By actual sunrise, we mean the actual crossing of the horizon by the Sun.
When the sun just below the horizon its rays enters earth’s atmosphere and refracted towards the earth. Refracted ray that reach us making it appears the sun reaches to horizon. This is the apparent sunrise. But actual sunrise occur when sun reach to horizon. Conversely apparent sunset occur slightly latter than actual sun set. Since light from sun already below the horizon it refract through atmosphere enabling us to see apparent sun set even sun has already set.

21. When the sun is overhead at noon, then the light coming from the sun has to travel a relatively shorter distance through the atmosphere to reach us. As a result, only a little of the blue colour of the white light is scattered (most of the blue light remains in it). Since the light coming from the overhead sun has almost all its components colors in the right proportion, therefore, the sun appears white.

Read more key points Visit Links:

Read more key points Visit Links:

Human eyes and Colorful world (commit to memory)
X Solved NCERT Questions: The Human Eye and the Colorful World

Human Eyes and Colorful world Science Guess Question solved X (10th)

X CBSE PHYSICS Human Eyes Questions for Practice

CBSE Class 10 Physics The Humane Eyes Study Notes

CBSE X Question Bank Human eyes and Colorful World

THE HUMAN EYE AND THE COLOURFUL WORLD E-Study Notes

14 November 2012

10th Solved questions For Chapter:The Human Eye and the Colorful World

1. What is the function of iris and pupil in the human eye?

2. Define : (i) Power of Accommodation (ii) Far point (iii) Near Point

3. 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? What are its causes? How it can be corrected?

4. Draw diagram showing dispersion of white light by a glass prism.

5. How is rainbow formed? Explain with diagram.

6. What did Newton demonstrated by his experiment?

7. Why stars appears to twinkle but the planets do not?

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

9. What happens to the image distance in the eye when we increase the distance of an object from the eye?

10. Why sky appears blue in colour?

11. Why does sun appears reddish early in the morning?

12. Why sky appears dark instead of blue to an astronaut?

13. Why danger signals are red in colour?

14. Why we see sunrise two minutes early and delayed sunset?

15. Why sun appears white at noon?

To see answer click link given below X Solved:The Human Eye and the Colorful World:

X CBSE Board (Guess Paper 2014) for Practice

1. A person can see only objects beyond 1m. From his eyes. Name the defect of the eye.
2. Out of light of blue and red colours which one is scattered most?
3. What is the function of crystalline lens in the human eye?
4. Which phenomenon is responsible for increasing the apparent length of the day by 4 minute?
5. What is the far point of a person suffering from Myopia.
6. What name is given to front transparent part of human eye?
7. Where do we see :(1) Concave and (2) Convex lens in bifocal lenses.
8. What is the nature of image formed by our eye?
9. Name the liquid which is present between eye lens and cornea.
10. Where does most of the refraction of light in an eye occurs?
11. Which kind of lens is an eye lens?
12. What is the cause of dispersion of light?
13. Under very dim light, we are able to see the objects but can not distinguish between colours why ?
14. What is the range of vision for normal human eye ?
15. How is the amount of light entering the eye controlled ?
16. What is the colour of danger signal? Why?
17. What is rainbow? How is rainbow formed?
18. State two causes of myopic vision.
19. How an uncorrected myopic eye sees far off objects.
20. What is presbyopia? Name the type of lens which can be used to correct presbyopia.
21. Explain why planet do not twinkle at night?
22. Explain about the colour of the sun at sunrise and sunset.
25. The near point of a hypermetropic eye is at 75 cm from the eye. What is the power of the lens required to enable him to read clearly a book held at 25 cm from the eye.
23. Define the term (1) Near point (2) Far point
24. Why is a normal eye not able to see clearly the object closer than 25 cm.

Read more key points Visit Links: Human eyes and Colorful world (commit to memory)
X Solved NCERT Questions: The Human Eye and the Colorful World
Human Eyes and Colorful world Guess Question solved X (10th)
X CBSE PHYSICS Human Eyes Questions for Practice
CBSE Class 10 Physics The Humane Eyes Study Notes
CBSE X Question Bank Human eyes and Colorful World
THE HUMAN EYE AND THE COLOURFUL WORLD E-Study Notes
Solved questions for Chapter: The Human Eye and the Colorful World   View
X (10th) Human eyes and Colorful World   View
CBSE Physics Chapter 11 Human Eye and Colorful World class   View

07 November 2012

CBSE X(10th) Human Eyes , Reflection and Refraction (Solution)

NCERT Solution, MCQs, Study Notes, Q & A

Question: What is the minimum distance between an object and its real image in case of a concave mirror?

Ans: The object and the image, both are at the centre of curvature of the concave mirror. The image formed is real and inverted. The minimum distance between object and its image = 0 units

Question: Why is the refractive index of atmosphere different at different altitudes?

Ans: it is because it is a mixture of differnet particles and gas molecules which often has diff. refractive indices

Question: When a light ray passes obliquely through the atmosphere in an upward direction, how does its path generally change?

Ans: When a light ray passes obliquely through the atmosphere in an upward direction, it 's path changes due to atmospheric refraction. This refraction happens because each atmospheric layer has a different optical density, due to which its path changes.

Question: State two factors on which the lateral displacement of the emergent ray in a rectangular glass slab depends for an oblique incident ray on the opposite face

Ans: The thickness of the glass slab and the optical density of the glass slab affect the lateral displacement of the emergent ray.

Question: Between which two points related to a concave mirror should an object be placed to obtain on a screen an image twice the size of the object?

Ans : Between center of curvature and Principal Focus

Question: What is meant by ‘total internal reflection’? State two essential conditions for total internal reflection to take place. With the help of a ray diagram, illustrate an application of total internal reflection.
Ans:

When light passes from one medium to other, it bends from its path which is called refraction. When a light ray passes from denser to rarer medium, at some angle of incidence it does not go out of the denser medium but just grazes along the boundary (i.e. angle of refraction = 90⁰). This angle of incidence is called critical angle.

Now, if you increase this angle of incidence, light ray is reflected back into the denser medium, which is called total internal reflection. The light ray is reflected every time it hits the boundary because angle if incidence is equal to angle of reflection, and is not able to come out of the medium. This phenomenon is called total internal reflection.

The conditions for total internal reflection are:
(i) the light ray must be travelling from optically denser medium to rarer medium and
(ii) the angle of incidence must be greater than the critical angle.

Optical fiber communication uses the principle of total internal reflection for transferring data through optical fibers.

Question: All the images formed by two plane mirrors inclined at an angle with respect to each other lie in a a) circle b) straight line c) sphere d) none of these

Ans: All the images formed by two plane mirrors inclined at an angle with respect to each other lie in a straight line. It happens in the barber shop.(Answer by JSUNIL)

Q. The image formed by a convex mirror of focal length 30cm is a quater of the object . what is the distance of the object from the mirror ?

Ans: h_i/ h_o = 1/4

h_i = image height

h_o= object height

now as

h_i/ h_o = -v/u = 1/4

we get

v = -u/4

so, using this in eq. (1), we get

1/30 = -4/u + 1/u

1/30 = -3/u

thus, the object distance will be

u = -90 cm

Q. A concave mirror produces 10cm long image of an object of height 2 cm . what is the magnification produced ?

Ans: The magnification of a curved mirror is given as

m = h_i/ h_o

here

h_i= height if the image = 10cm

h_o= height of the object = 2cm

so, we have

m = 10cm / 2cm

so magnification will be m = 5

Question: If a fish inside a pond is viewing a man outside the pond then, how will the image of the man appear?

Ans: Due to the refraction of light rays, to the fish, the man would appear to be higher than he actually is.

Question: A man sits in a optician 's chair ,looking into a plane mirror which is 2m away from him and views the image of a chart which faces the mirror and is 50 cm behind his head.How far away from his eyes does the chart appears to be.

Ans: The distance between the eye and chart will be the sum of the distance between eye and the mirror and the miror and chart image. So we will get In the mirror the chart appears to be 2m + 2m + 0.5m = 4.5m away.

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