Light+Refraction

=Light: Refraction of light= media type="custom" key="25209584"

Refraction-
Refraction is the bending of a wave when it enters a medium where its speed is different. The refraction of light when it passes from a fast medium to a slow medium bends the light ray toward the normal to the boundary between the two media.



When light enters from rarer to denser medium, it bends towards the normal. When it passes from denser to rarer medium, it bends away from the normal. The amount of bending is affected by refractive index of the medium.


 * Refractive Index ** - The index of refraction is defined as the speed of light in vacuum divided by the speed of light in the medium

Definitions related to lenses and image formation through lenses.

Convex lens- A lens which is thicker in the middle than on the ends.

Concave lens- A lens which is thinner in the middle than on the ends.

Focus - For a positive (converging) lens or mirror, the focal points of the element are the points at which a ray, approaching the element parallel to the optical axis, crosses the optical axis on the opposite side. For a negative (diverging) lens, the focal points are the points at which the backward extension of the diverging ray intersects the optical axis.

Principal axis - the line passing through the centres of curvature of the lens Principal focus - a point on the principal axis where rays of light parallel to the principal axis converge Focal length - the horizontal distance between the principal focus and the optical centre of the lens Optical centre -an imaginary point inside a lens through which a light ray is able to travel without being deviated Centre of curvature -the centre of the sphere of which the lens surface is part Ray diagrams are constructed by taking the path of three distinct rays from a point on the object:

A) a ray parallel to the principal axis, which refracts through the lens, passes through the principal focus. B) a ray passing through the optical centre of the lens, passes without deviation.

C) a ray passing through the principal focus(on the same side as the object) and being refracted through the lens, emerges parallel to the principal axis.

Formation of an image from an object positioned between f and the lens, at f, between f and 2f and at 2f from the lens:



POSITION OF OBJECT: If the object is located at infinity: NATURE AND POSITION OF IMAGE  1. The image will form at the principal focus (F).  2. The image will be real and inverted.  3. The image will be very small in size.

POSITION OF OBJECT:
 * When the Object is Placed beyond 2F **

NATURE AND POSITION OF IMAGE 1. The image will form between F and 2F 2. The image will be real and inverted. 3. The image will be diminished than the size of object.

POSITION OF OBJECT: When the object is placed at 2F NATURE AND POSITION OF IMAGE 1. The image will form at 2F. 2. The image will be real and inverted. 3. The image will be equal to the size of object.



POSITION OF OBJECT:

When the object is placed between F and 2F

NATURE AND POSITION OF IMAGE

1. The image will form beyond 2F.

2. The image will be real and inverted.

3. The image will be magnified.



POSITION OF OBJECT: When the object is placed at F NATURE AND POSITION OF IMAGE 1. The image will form at infinity 2. The image will be real and inverted. 3. The image will be highly magnified.



POSITION OF OBJECT:

When the object is placed between O and F

NATURE AND POSITION OF IMAGE

1. The image will form beyond 2F

2. The image will be virtual and erect.

3. The image will be magnified.

Srtucture of eye and vision: E ye is like a camera. The external object is seen like the camera takes the picture of any object. Light enters the eye through a small hole called the ** pupil ** and is focused on the ** retina **, which is like a camera film. Eye also has a focusing ** lens **, which focuses images from different distances on the retina. The colored ring of the eye, the ** iris **, controls the amount of light entering the eye. It closes when light is bright and opens when light is dim. A tough white sheet called ** sclera ** covers the outside of the eye. Front of this sheet (sclera) is transparent in order to allow the light to enter the eye, the ** cornea **. Ciliary muscles in ciliary body control the focusing of lens automatically. ** Choroid ** forms the vascular layer of the eye supplying nutrition to the eye structures. Image formed on the retina is transmitted to brain by ** optic nerve **. The image is finally perceived by brain. A jelly like substance called ** vitreous ** humor fill the space between lens and retina. The lens, iris and cornea are nourished by clear fluid, ** aqueous ** humor, formed by the ciliary body and fill the space between lens and cornea. This space is known as ** anterior chamber **. The fluid flows from ciliary body to the pupil and is absorbed through the channels in the angle of anterior chamber. The delicate balance of aqueous production and absorption controls pressure within the eye. media type="custom" key="25251758"

The lens is constantly changing shape depending on whether we are looking at objects close to us or far away. The bending of the lens is called accommodation. When adults become old, their lens becomes rigid and they cannot reflect light properly to the back of their eye and need reading glasses. A really cool thing about the lens is that it reflects the light upside down and inverted toward the back of the eye (retina). Our brain must switch the image back right side up or we would have serious perception issues.

The first layer of cells to be activated by light are called the rods and cones. Rods see only black and white and are spread throughout the outside of the retina. Cones see color and are located in the center of the retina known as the fovea. Since the cones are located in the fovea (in the center of the retina) we see color objects better if they are directly in front of us. Since rods are located on the periphery of the retina- we see black and white better in out peripheral vision.

Following site is good to refer the structure of eye: http://www.internal.schools.net.au/edu/lesson_ideas/optics/optics_wksht2_p1.html

Hyperopia (Farsightedness)
> >  Farsightedness, or hyperopia, as it is medically termed, is a vision condition in which distant objects are usually seen clearly, but close ones do not come into proper focus. Farsightedness occurs if your eyeball is too short or the cornea has too little curvature, so light entering your eye is not focused correctly > .

<span style="background-color: #ffffff; color: #00b1ff; font-family: Arial,sans-serif; font-size: 1.2857142857142858em;">Myopia (Nearsightedness)
> earsightedness, or myopia, as it is medically termed, is a vision condition in which near objects are seen clearly, but distant objects do not come into proper focus. Nearsightedness occurs if your eyeball is too long or the cornea has too much curvature, so the light entering your eye is not focused correctly.



=<span style="background-color: #ffffff; color: #444444; font-family: Arial,sans-serif; font-size: 1.2857142857142858em;">Presbyopia = <span style="background-color: #ffffff; color: #666666; display: block; font-family: Arial,sans-serif; font-size: 14px;"> ** Presbyopia ** is a vision condition in which the crystalline lens of your eye loses its flexibility, which makes it difficult for you to focus on close objects. Presbyopia may seem to occur suddenly, but the actual loss of flexibility takes place over a number of years. Presbyopia usually becomes noticeable in the early to mid-40s. Presbyopia is a natural part of the aging process of the eye. It is not a disease, and it cannot be prevented. <span style="background-color: #ffffff; color: #666666; display: block; font-family: Arial,sans-serif; font-size: 14px;"> =<span style="background-color: #ffffff; color: #444444; font-family: Arial,sans-serif; font-size: 1.2857142857142858em;">Astigmatism = ** Astigmatism ** is a vision condition that causes blurred vision due either to the irregular shape of the cornea, the clear front cover of the eye, or sometimes the curvature of the lens inside the eye. An irregular shaped cornea or lens prevents light from focusing properly on the retina, the light sensitive surface at the back of the eye. As a result, vision becomes blurred at any distance. Astigmatism is a very common vision condition. Most people have some degree of astigmatism. Slight amounts of astigmatism usually don't affect vision and don't require treatment. However, larger amounts cause distorted or blurred vision, eye discomfort and headaches. <span style="background-color: #ffffff; color: #666666; display: block; font-family: Arial,sans-serif; font-size: 14px;">Cylindrical lenses are used for correction of this problem.

<span style="background-color: #ffffff; color: #00b1ff; font-family: Arial,sans-serif; font-size: 1.2857142857142858em;">Cataract
A cataract is a cloudy or opaque area in the normally clear lens of the eye. Depending upon its size and location, it can interfere with normal vision. Most cataracts develop in people over age 55, but they occasionally occur in infants and young children. Usually cataracts develop in both eyes, but one may be worse than the other. > Bibliography: http://micro.magnet.fsu.edu/optics/lightandcolor/images/refractionfigure1.jpg http://physics.tutorvista.com/light/convex-lens.html http://www.myeyeworld.com/files/eye_structure.htm http://www.appsychology.com/Book/Biological/vision.htm http://www.aoa.org/patients-and-public/eye-and-vision-problems#hyperopia http://medical.cdn.patient.co.uk/images/349.gif