Chapter 1:Chemical Reaction And Equations
Chapter 2:Acids, Bases and Salts
Chapter 3:Metals and Non-metals
Chapter 4:Carbon and Its Compounds
Chapter 5: Periodic Classification of Elements
Chapter 10: Light Reflection and Refraction
Chapter 11:Human Eye and Colourful World
The human eye uses light and enables us to see objects around us and it is one of the most valuable and sensitive sense organs. It enables us to see the wonderful world and the colours around us It is similar to a camera. We all have been gifted with two eyes which gives a wider field of view.
THE HUMAN EYE:
The human eye has been called the most complex organ in our body. Eye is a natural optical instrument. It is present in the form of eyeball in the sockets of our skull. Its diameter is approximately 2.5 cm the eye includes- cornea, iris, pupil, lens, ciliary muscles, retina, nerve cells, optic nerve, and yellow spot, aqueous and vitreous humor, and suspensory ligament.
Cornea
Cornea is the transparent substance and the front part of our eye, which covers the pupil and the iris. It functions like a window that controls and focuses the entry of light into the eye.
Iris:
The colored part of the eye which helps regulate the amount of light entering the eye. When there is bright light, the iris contracts the pupil and reduce the amount light enter the eyes And when there is low light, the iris opens up the pupil to let in more light may enter the eyes
Pupil:
The function of the pupil is clearly that of controlling the amount of light entering the eye, and hence the light reflex.
lens:
Situated behind the pupil is a colorless, transparent structure called the crystalline lens. with the help of ciliary muscles, it changes its shape to focus light on the retina. It becomes thinner to focus distant objects and becomes thicker to focus nearby objects.
Sclera:
The sclera is the opaque, fibrous, tough, protective outer layer of the eye. The sclera provides protection and form
Retina::
The retina is a delicate membrane having enormous
number of light-sensitive cells It converts images formed by the lens into electrical signals.These signals are
sent to the brain via the optic nerves.
Cones:
Cones are cells which are more sensitive to bright light cone cell cause the sensaton of colour of things
Rode:
Rods are cells which are more sensitive to dim lights.rode cell help in seeing a object in dim light
Working of Eye:
Light enters the eye
through cornea and pass through the pupil and fall on eys-lens .Since eys-lens is an convex lens so it converge the light rays and produce a inverted real image of object on retina The retina is a delicate membrane having enormous
number of light-sensitive cells. The light-sensitive cells get activated
upon illumination and generate electrical signals. These signals are
sent to the brain via the optic nerves. The brain interprets these signals and finally, processes the information so that we perceive objects
Power of Accommodation:
The ability of the eye lens to adjust its focal length is called
accommodation.
ii)The minimum distance, at
which objects can be seen most distinctly without strain, is called the
least distance of distinct vision. It is also called the near point of the eye. It at about 25 cm from the eyes
iii)The farthest point upto which the eye can see objects clearly is
called the far point of the eye. It is infinity for a normal eye.
catarac:
When eyes becomes milky and
cloudy. This condition is called cataract. This causes partial or complete
loss of vision. It is possible to restore vision through a cataract surgery
DEFECTS OF VISION:
There are mainly three common refractive defects of vision. These
are
(i) myopia or near-sightedness,
(ii) Hypermetropia or farsightedness,
(iii) Presbyopia.
Myopia or near-sightedness:
Myopia is also known as near-sightedness. A person with myopia
can see nearby objects clearly but
cannot see distant objects distinctly.
This defect may arise due
(i) excessive curvature of the eye
lens,
(ii) elongation of the eyeball.
CORRECTION:
This defect can be corrected by
using a concave lens of suitable
power
Hypermetropia or farsightedness,:
Hypermetropia is also known as far-sightedness. A
person with hypermetropia can see distant objects
clearly but cannot see nearby objects distinctly.
This defect may arise due
(i) the focal length of the eye lens is too
long,
(ii) the eyeball has become too small
CORRECTION:
This defect
can be corrected by using a convex lens
Presbyopia:
it difficult to see
nearby objects comfortably and distinctly without
corrective eye-glasses. This defect is called Presbyopia.
This defect may arise due
the gradual weakening of the ciliary muscles and diminishing
flexibility of the eye lens
REFRACTION OF LIGHT THROUGH A PRISM:
Angle of the prism:The angle between its two lateral faces is called the angle of the prism
Angle of deviation:The peculiar shape of the prism makes the emergent ray bend at an angle to the direction of the incident ray.Here ∠D is the angle of deviation
DISPERSION OF LIGHT:
The splitting
of light into its seven colours when it pass through a medium like prism is called dispersion.
Spectrum: The band of the coloured components of a light beam is called its spectrum.
The rainbow :
A rainbow is a natural spectrum appearing in the sky after a
rain. It is caused by dispersion of sunlight by
tiny water droplets, present in the atmosphere. A rainbow is
always formed in a direction opposite to that of the Sun.
ATMOSPHERIC REFRACTION :
Twinkling of stars : The starlight, on entering the earth’s atmosphere, and reach the eyes due to atmospheric refraction light intensity increase and decrease continuously and star appears twinkling
Star appears slightly higher :due to atmospheric refraction
starlight bend towards the normal, the apparent position of the
star is slightly different from its actual position so The star
appears slightly higher than its actual position
Advance sunrise and delayed sunset :The Sun is visible to us about 2 minutes before the
actual sunrise, and about 2 minutes after the actual
sunset because of atmospheric refraction.
SCATTERING OF LIGHT:
Tyndall Effect: The phenomenon of scattering of light by the colloidal particles
Q. Why is the colour of the clear Sky Blue?
The scattering of blue component of the sunlight by fine partical present in the atmosphere cause the blue colour of the sky
Colour of the Sun at Sunrise and Sunset
Light from the Sun near the horizon passes
through thicker layers of air and larger distance
in the earth’s atmosphere before reaching our eyes So, the blue light
scattered away by the particles (due to shorter wavelengths) . Therefore, the light that reaches our
eyes is of longer wavelengths(like Red) . This gives rise to the reddish appearance
of the Sun.
Chapter 1:Chemical Reaction And Equations
Chapter 2:Acids, Bases and Salts
Chapter 3:Metals and Non-metals
Chapter 4:Carbon and Its Compounds
Chapter 5: Periodic Classification of Elements
Chapter 10: Light Reflection and Refraction
Chapter 11:Human Eye and Colourful World