THE
HUMAN EYE AND THE COLORFUL WORLD
The image of an object seen persists on the retina for 1/16 second even after the removal of the object. This continuance of sensation of eye for some timed is called persistence of vision.
Colour blindness: It is said to occur when a person cannot distinguish between colours though his vision may otherwise be normal.
Power of accommodation:
It is the ability of the eye to observe distinctly the object situated at widely different distances from the eye on account of change in focal length of eye.
Far Point of the Eye: It is the farthest point at which the object can be seen clearly. For a normal eye, the far point lies at infinity.
Near point of the Eye: It is the closest point at which an object can be seen clearly. For normal eye, the near point lies at 25 cm from the eye(least distance of distinct vision)
Defects of vision: Following are the common defects of vision (or) refractive defects of eye:
1. Myopia(or) Short sightedness:
It is that defect of human eye by virtue of which it can see clearly the objects lying at short distances from it. But the far off objects cannot be seen by the Myopic Eye.
Possible causes of Myopia:
1. Increase in the length of the eye ball as if distance of the retina from the eye has increased.
2. Decrease in focal length of eye lens when the eye is fully relaxed.
Remedy:
To correct a myopic eye, the person has to wear spectacle with a concave lens of suitable focal
length. (i.e.) the focal length of concave lens is equal to the distance of the far point of the myopic
eye.
Question: The far point of a myopic eye is at 50 cm. Calculate the power of the lens to correct the
vision.
Ans: The focal length of the concave lens to be used f=-50cm. Therefore P=1/f (metre) = 1/-0.5 =
-2D
2. Hypermetropia (or) Long sightedness:
It is that defect of a human eye by virtue of which it can see clearly the objects lying at large
distances from it but the nearby objects cannot be seen clearly.
Possible causes of Hypermetropia:
(1) Decrease in length of eye ball as if distance of retina from the eye lens has decreased (2) Increase
in the focal length of the eye lens when the eye is fully relaxed.
Remedy: To correct a hypermetropic eye, the person has to wear spectacle with a convex lens of
suitable focal length.
The focal length of the convex lens is given by f=(x d) / (x-d); '
where x is the distance of near point of defective eye;
d is the distance of near point of normal eye(25 cm)
Questions 2. The near point of Hypermetropic eye is 75 cm from the eye. What is the power of the
Ans: Focal length of convex lens to be used is given by f=xd/x-d.
Here x= 75 cm and d=25 cm.
Therefore, f=75 x 25 / 75-25 = 37.5 cm.
3. Presbyopia: It is that defect of human eye due to which an old person cannot read and write
comfortably.
Remedy: To correct this, an old person has to use spectacles with a convex lens of suitable focal
length
o When a person suffers from both myopia and hypermetropia his spectacles have bi-focal lenses (i.e) both concave and convex lenses.
DISPERSION:
It is the phenomena of splitting of white light into its constituent seven colours on passing through a
Glass prism.
Cause of Dispersion:
Different wavelengths of light having different colours moves with different speed in a medium,
though they travel with a same velocity in air or vacuum. And hence the different colours deviate
through different angles on passing through the glass prism. That is why they split on coming out of
the prism along different directions.
Visible spectrum: The band of seven colours obtained due to the dispersion of white light is called a
visible spectrum (VIBGYOR).
Application of dispersion:
RAINBOW: It is a concentric coloured circular arc in the sky when the sun shines on rain drops
during or after a shower.
Essential conditions for observing a rainbow is that the observer must stand with his back towards the sun.
The formation of rainbow is due to the dispersion of white light from the sun and the phenomenon of
total internal reflection of light from the water droplets suspended in the air after a shower
Total internal reflection:
When light travels from denser to rarer medium incident on the interface separating two media at an
angle larger than a particular angle called critical angle (which is a constant for a given pair of media) will be totally reflected back into the denser medium
ATMOSPHERIC REFRACTION:
Different layers of atmosphere are at different temperature. Due to this the optical density of different layers are different.
As you go upwards, the atmosphere becomes rarified. So the Refractive Index decreases as we go upwards. So, the light from the sun or any other star undergoes refraction.
SCATTERING OF LIGHT:
• As the sun light travels through the earth atmosphere, it gets scattered by a large number of
molecules.
• Scattering of light takes place when the size of the scattering molecule is very very small when
compared to the wavelength of light.
• Intensity of scattered light (Is) varies inversely to the 4th power of the wave length (λ) of incident
light.
• Blue colour of sky is due to the scattering of sun light. Since the intensity of scattered light varies
inversely as a 4th power of wave length, the blue colour (shorter wave length) is scattered much more strongly. Hence the sky appears blue.
The clouds are at lower height. They are seen due to the scattering of light from the lower part of
atmosphere which contains large number of dust particles and water drop lets whose size is very large when compared to wave length of different colours in sun light. So all the wave lengths are scattered equally and hence it appears white.
• The sun looks reddish at the time of sun rise and sun set: At the time sun rise and sun set the sun is
• Danger signals are Red: It is because wave length of red colour is large and intensity of scattered
light 1/λ^4 the red light gets least scattered and can be seen from maximum distance.
• Sky appears dark to an Astronaut: It is because at such huge heights there is nothing to scatter sun
light. Therefore, the sky appears dark.
Useful study link from: http://jsuniltutorial.weebly.com/the-human-eye-and-the-colourful-world.html
10th Human eye and Atmospheric refraction Notes
Download File
Human Eye & Atmospheric Refraction Solved paper -1
Download File
Human Eye & Atmospheric Refraction Solved paper -2
Download File
Human Eye & Atmospheric Refraction Solved paper -3
Download File
Human Eye & Atmospheric Refraction Solved paper -4
Download File
class 10 Human Eye Solved Numerical Test Paper -5
Download File
Human
eye can be treated as an optical instrument. Light rays coming from the object
to be seen enter the eye through Cornea and fall on the eye lens through the
pupil of the eye.
Eye lens being double
convex lens forms a real inverted and smaller image of the object on the
retina.
The retina contains
numerous light sensitive cells which are activated by the light falling on the
retina and generate electrical signals
which are sent to brain via optic nerve and the brain processes
this information and we perceive objects as they are.
Persistence
of vision:
The image of an object seen persists on the retina for 1/16 second even after the removal of the object. This continuance of sensation of eye for some timed is called persistence of vision.
Colour blindness: It is said to occur when a person cannot distinguish between colours though his vision may otherwise be normal.
Power of accommodation:
It is the ability of the eye to observe distinctly the object situated at widely different distances from the eye on account of change in focal length of eye.
Far Point of the Eye: It is the farthest point at which the object can be seen clearly. For a normal eye, the far point lies at infinity.
Near point of the Eye: It is the closest point at which an object can be seen clearly. For normal eye, the near point lies at 25 cm from the eye(least distance of distinct vision)
Defects of vision: Following are the common defects of vision (or) refractive defects of eye:
1. Myopia(or) Short sightedness:
It is that defect of human eye by virtue of which it can see clearly the objects lying at short distances from it. But the far off objects cannot be seen by the Myopic Eye.
Possible causes of Myopia:
1. Increase in the length of the eye ball as if distance of the retina from the eye has increased.
2. Decrease in focal length of eye lens when the eye is fully relaxed.
Remedy:
To correct a myopic eye, the person has to wear spectacle with a concave lens of suitable focal
length. (i.e.) the focal length of concave lens is equal to the distance of the far point of the myopic
eye.
Question: The far point of a myopic eye is at 50 cm. Calculate the power of the lens to correct the
vision.
Ans: The focal length of the concave lens to be used f=-50cm. Therefore P=1/f (metre) = 1/-0.5 =
-2D
2. Hypermetropia (or) Long sightedness:
It is that defect of a human eye by virtue of which it can see clearly the objects lying at large
distances from it but the nearby objects cannot be seen clearly.
Possible causes of Hypermetropia:
(1) Decrease in length of eye ball as if distance of retina from the eye lens has decreased (2) Increase
in the focal length of the eye lens when the eye is fully relaxed.
Remedy: To correct a hypermetropic eye, the person has to wear spectacle with a convex lens of
suitable focal length.
The focal length of the convex lens is given by f=(x d) / (x-d); '
where x is the distance of near point of defective eye;
d is the distance of near point of normal eye(25 cm)
Questions 2. The near point of Hypermetropic eye is 75 cm from the eye. What is the power of the
lens required to enable him to read clearly a book held at 25 cms
from the eye?
Ans: Focal length of convex lens to be used is given by f=xd/x-d.
Here x= 75 cm and d=25 cm.
Therefore, f=75 x 25 / 75-25 = 37.5 cm.
Hence power p=1/f (meter)
= 1/.375 = 2.66D
3. Presbyopia: It is that defect of human eye due to which an old person cannot read and write
comfortably.
Remedy: To correct this, an old person has to use spectacles with a convex lens of suitable focal
length
o When a person suffers from both myopia and hypermetropia his spectacles have bi-focal lenses (i.e) both concave and convex lenses.
DISPERSION:
It is the phenomena of splitting of white light into its constituent seven colours on passing through a
Glass prism.
Cause of Dispersion:
Different wavelengths of light having different colours moves with different speed in a medium,
though they travel with a same velocity in air or vacuum. And hence the different colours deviate
through different angles on passing through the glass prism. That is why they split on coming out of
the prism along different directions.
Visible spectrum: The band of seven colours obtained due to the dispersion of white light is called a
visible spectrum (VIBGYOR).
Application of dispersion:
RAINBOW: It is a concentric coloured circular arc in the sky when the sun shines on rain drops
during or after a shower.
Essential conditions for observing a rainbow is that the observer must stand with his back towards the sun.
The formation of rainbow is due to the dispersion of white light from the sun and the phenomenon of
total internal reflection of light from the water droplets suspended in the air after a shower
Total internal reflection:
When light travels from denser to rarer medium incident on the interface separating two media at an
angle larger than a particular angle called critical angle (which is a constant for a given pair of media) will be totally reflected back into the denser medium
ATMOSPHERIC REFRACTION:
Different layers of atmosphere are at different temperature. Due to this the optical density of different layers are different.
As you go upwards, the atmosphere becomes rarified. So the Refractive Index decreases as we go upwards. So, the light from the sun or any other star undergoes refraction.
Example: Twinkling of
stars, early sun rise and delayed sun set.
SCATTERING OF LIGHT:
• As the sun light travels through the earth atmosphere, it gets scattered by a large number of
molecules.
• Scattering of light takes place when the size of the scattering molecule is very very small when
compared to the wavelength of light.
• Intensity of scattered light (Is) varies inversely to the 4th power of the wave length (λ) of incident
light.
• Blue colour of sky is due to the scattering of sun light. Since the intensity of scattered light varies
inversely as a 4th power of wave length, the blue colour (shorter wave length) is scattered much more strongly. Hence the sky appears blue.
White
colour of Clouds:
The clouds are at lower height. They are seen due to the scattering of light from the lower part of
atmosphere which contains large number of dust particles and water drop lets whose size is very large when compared to wave length of different colours in sun light. So all the wave lengths are scattered equally and hence it appears white.
• The sun looks reddish at the time of sun rise and sun set: At the time sun rise and sun set the sun is
near the horizon. So the rays from the sun have to travel large part of
atmosphere. Since the intensity of scattered light is
proportional to 1/λ^4 most of the blue light is scattered away. Only red colours
which is least scattered enter our eye and hence the sun looks red.
• Danger signals are Red: It is because wave length of red colour is large and intensity of scattered
light 1/λ^4 the red light gets least scattered and can be seen from maximum distance.
• Sky appears dark to an Astronaut: It is because at such huge heights there is nothing to scatter sun
light. Therefore, the sky appears dark.
Useful study link from: http://jsuniltutorial.weebly.com/the-human-eye-and-the-colourful-world.html
10th Human eye and Atmospheric refraction Notes
Download File
Human Eye & Atmospheric Refraction Solved paper -1
Download File
Human Eye & Atmospheric Refraction Solved paper -2
Download File
Human Eye & Atmospheric Refraction Solved paper -3
Download File
Human Eye & Atmospheric Refraction Solved paper -4
Download File
class 10 Human Eye Solved Numerical Test Paper -5
Download File
Read more key points Visit Links:
|
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
|
No comments:
Post a Comment