DEFECTS IN VISION

                                   



      Myopia: Short-sightedness or Myopia is a condition when the person is able to see the objects that are nearby very clearly and is unable to view the distant objects easily. This defect arises as the image of the object that is supposed to from at the retina forms in front of the retina. The reasons behind this defect is the elongation of the lens.Since thinner the lens,less is the focal length,so that's why  the focal length of the lens decreases and consequently causes the focus,which was firstly on the retina,comes nearer to the lens.
  

    Hypermetropia: Long- sightedness or Hypermetropia is a condition where the person is able to see the objects that are distant clearly and is unable to view the nearby objects clearly. This defect arises as the image of the object that is supposed to from at the retina forms behind the retina.  A person with Hypermetropia can read comfortably only when reading material is kept beyond 25 cm from the eye. The reasons behind this defect is thickening of the eye lens.Since,thicker the lens,more is the focal length,so that's why the focal length of the lens increases and consequently causes the focus ,which was firstly on the retina,to move away, fartther from the lens.

 
     Presbyopia: Ageing leads to a decrease in the power of accommodation of the Human eye. Most of the people with this defect find it extremely difficult to see the nearby objects with an ease. The diminishing flexibility of the eye lens and the weakening of the ciliary muscles leads to this defect. This defect can be corrected with the help of corrective eye glasses. Bi-focal lenses are used to help people who have both the defects of vision (Myopia and Hypermetropia).

CAN U TRUST UR EYES?

A JOURNEY THROUGH THE HUMAN EYE

human eye...............

The human eye is an organ that reacts to light and has several purposes. As a conscious sense organ, the mammalian eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth. The human eye can distinguish about 10 million colors.
Similar to the eyes of other mammals, the human eye's non-image-forming photosensitive ganglion cells in the retina receive light signals which affect adjustment of the size of the pupil, regulation and suppression of the hormone melatonin and entrainment of the body clock.

 1. vitreous body 2. ora serrata 3. ciliary muscle 4. ciliary zonules 5. Schlemm's canal 6. pupil 7. anterior chamber 8. cornea 9. iris 10. lens cortex 11. lens nucleus 12. ciliary process 13. conjunctiva 14. inferior oblique muscle 15. inferior rectus muscle 16. medial rectus muscle 17. retinal arteries and veins 18. optic disc 19. dura mater 20. central retinal artery 21. central retinal vein 22. optic nerve 23. vorticose vein 24. bulbar sheath 25. macula 26. fovea 27. sclera 28. choroid 29. superior rectus muscle 30. retina

General properties

The eye is not shaped like a perfect sphere, rather it is a fused two-piece unit. The smaller frontal unit, more curved, called the cornea is linked to the larger unit called the sclera. The corneal segment is typically about 8 mm (0.3 in) in radius. The sclerotic chamber constitutes the remaining five-sixths; its radius is typically about 12 mm. The cornea and sclera are connected by a ring called the limbus.

Human Iris, Blue type

The iris – the color of the eye – and its black center, the pupil, are seen instead of the cornea due to the cornea's transparency. To see inside the eye, an ophthalmoscope is needed, since light is not reflected out. The fundus (area opposite the pupil) shows the characteristic pale optic disk (papilla), where vessels entering the eye pass across and optic nerve fibers depart the globe.

Components

The eye is made up of three coats, enclosing three transparent structures. The outermost layer, known as the fibrous tunic, is composed of the cornea and sclera. The middle layer, known as the vascular tunic or uvea, consists of the choroid, ciliary body, and iris. The innermost is the retina, which gets its circulation from the vessels of the choroid as well as the retinal vessels, which can be seen in an ophthalmoscope.

Blood vessels can be seen within the sclera, as well as a strong limbal ring around the iris.

Within these coats are the aqueous humour, the vitreous body, and the flexible lens. The aqueous humour is a clear fluid that is contained in two areas: the anterior chamber between the cornea and the iris, and the posterior chamber between the iris and the lens. The lens is suspended to the ciliary body by the suspensory ligament (Zonule of Zinn), made up of fine transparent fibers. The vitreous body is a clear jelly that is much larger than the aqueous humour present behind the lens, and the rest is bordered by the sclera, zonule, and lens. They are connected via the pupil.

Pupil constriction

Lenses cannot refract light rays at their edges as well as they can closer to the center. The image produced by any lens is therefore somewhat blurry around the edges (spherical aberration). It can be minimized by screening out peripheral light rays and looking only at the better-focused center. In the eye, the pupil serves this purpose by constricting while the eye is focused on nearby objects. In this way the pupil has a dual purpose: to adjust the eye to variations in brightness and to reduce spherical aberration.

Effects of aging

There are many diseases, disorders, and age-related changes that may affect the eyes and surrounding structures.
As the eye ages, certain changes occur that can be attributed solely to the aging process. Most of these anatomic and physiologic processes follow a gradual decline. With aging, the quality of vision worsens due to reasons independent of diseases of the aging eye. While there are many changes of significance in the non-diseased eye, the most functionally important changes seem to be a reduction in pupil size and the loss of accommodation or focusing capability (presbyopia). The area of the pupil governs the amount of light that can reach the retina. The extent to which the pupil dilates decreases with age, leading to a substantial decrease in light received at the retina. In comparison to younger people, it is as though older persons are constantly wearing medium-density sunglasses. Therefore, for any detailed visually guided tasks on which performance varies with illumination, older persons require extra lighting. Certain ocular diseases can come from sexually transmitted diseases such as herpes and genital warts.

SOAPS AND DETERGENTS

Soaps are sodium salts of long chain carboxylic acids. The soapiness in soap comes from the sodium salts of fatty acids like stearic acid, oleic acid andpalmitic acid.
Sodium Oleate  Sodium Palmitate  

The ionic end of the soap dissolves in water while the carbon chain dissolves in oil. The positively charged heads of the soap molecules repel each other and form a closed structure. This structure is called amicelle. The dirt is pulled and absorbed into the centre of the micelle. This property of soap makes it anemulsifier.

Sometimes, soaps don’t lather well with hard water. Hard water contains calcium and magnesium, which combine with soap molecules to form insoluble precipitates.

Detergents consist of long chain molecules such as sodium n-dodecyl benzene sulphonate and sodium n- dodecyl sulphate. The charged ends of these compounds do not form insoluble precipitates with the calcium and magnesium ions in water.  Detergents are

used in shampoos and products for cleaning clothes.

             

structure of sodium n-dodecyl benzene sulphonate,

structure of sodium n-dodecyl sulphate

SOURCE: www.learnnext.com

reproduction in human beings..........................

 sexual reproduction in human beings

Sexual intercourse (or coitus or copulation) is, broadly, the insertion and thrusting of a male's penis, usually when erect, into a female's vagina for the purposes of sexual pleasure or reproduction; also known as vaginal intercourse or vaginal sex. Other forms of penetrative sexual intercourse include penetration of the anus by the penis (anal sex), penetration of the mouth by the penis or oral penetration of the vulva or vagina (oral sex), sexual penetration by the fingers (fingering), and sexual penetration by use of a strap-on dildo. These activities involve physical intimacy between two or more individuals and are usually used among humans solely for physical or emotional pleasure and commonly contribute to human bonding.A variety of views concern what constitutes sexual intercourse or other sexual activity and their effects on health. While the term sexual intercourse, particularly the variant coitus, most commonly denotes penile-vaginal penetration and the possibility of creating offspring (the fertilization process known as reproduction), oral sex (especially when penetrative) and particularly penile-anal sex are also commonly considered sexual intercourse. Non-penetrative sex acts (such as non-penetrative forms of cunnilingus or mutual masturbation) have been termed outercourse, but may additionally be among the sexual acts contributing to human bonding and considered sexual intercourse The term sex, often a shorthand for sexual intercourse, can mean any form of sexual activity. Because people can be at risk of contracting sexually transmitted infections during these activities, though the transmission risk is significantly reduced during non-penetrative sex,safe sex practices are advised.

Health effects

Benefits

In humans, sexual intercourse and sexual activity in general have been reported to produce health benefits as varied as improved sense of smell, stress and blood pressure reduction,increased immunity, and decreased risk of prostate cancer. Sexual intimacy, as well as orgasms, increases levels of the hormone oxytocin, also known as "the love hormone", which helps people bond and build trust. Sexual intercourse and sexual activity in general are aspects of many mood repair strategies, which mean they can be used to help dissipate feelings of sadness or depression.

Risks

Sexually transmitted infections (STIs) can be spread by person-to-person sexual contact, especially penetrative sexual intercourse. There are 19 million new cases of sexually transmitted infections every year in the U.S., and, in 2005, the World Health Organization estimated that 448 million people aged 15–49 were being infected a year with curable STIs (such as syphilis, gonorrhea and chlamydia).
STIs are caused by bacteria, viruses and parasites, which are passed from person to person during sexual contact. Some, in particular HIV and syphilis, can also be passed in other ways, including from mother to child during pregnancy and childbirth, through blood products, and by shared hypodermic needles. Gonococcal or chlamydial infections often produce no symptoms. Untreated chlamydial infection can lead to female infertility and ectopic pregnancy. Human papillomavirus can lead to genital and cervical cancers. Syphilis can result in stillbirths and neonatal deaths. Untreated gonococcal infections result in miscarriages, preterm births and perinatal deaths. Infants born to mothers with untreated gonorrhoea or chlamydia can develop neonatal conjunctivitis (a serious eye infection), which can lead to blindness. Hepatitis B can also be transmitted through sexual contact. Globally, there are about 350 million chronic carriers of hepatitis B.

Social effects

Adults

Some researchers, such as Alex Comfort, posit three potential advantages of sexual intercourse in humans, which are not mutually exclusive: reproductive, relational, and recreational. While the development of the birth-control pill and other highly effective forms of contraception in the mid- and late 20th century increased people's ability to segregate these three functions, they still overlap a great deal and in complex patterns. For example: A fertile couple may have sexual intercourse while contracepting not only to experience sexual pleasure (recreational), but also as a means of emotional intimacy (relational), thus deepening their bonding, making their relationship more stable and more capable of sustaining children in the future (deferred reproductive). This couple may emphasize different aspects of sexual intercourse on different occasions, being playful during one episode of sexual intercourse (recreational), experiencing deep emotional connection on another occasion (relational), and later, after discontinuing contraception, seeking to achieve pregnancy (reproductive, or more likely reproductive and relational).

Adolescents

With regard to adolescent sexuality, sexual intercourse is usually for relational and recreational purposes as well. However, teenage pregnancy is often disparaged, and research suggests that the earlier onset of puberty for children puts pressure on children and teenagers to act like adults before they are emotionally or cognitively ready,and thus are at risk to suffer from emotional distress as a result of their sexual activities. Some studies have concluded that engaging in sexual activity leaves adolescents, especially girls, with higher levels of stress and depression. A majority of adolescents in the United States have been provided with some information regarding sexuality,though there have been efforts among social conservatives in the United States government to limit sex education in public schools to abstinence-only sex education curricula.

concave and convex lenses

Lenses are the most used things in optical devices like microscopes and telescopes. Bi-convex and bi-concave lenses are the most popular ones in use among school labs. Lenses use the phenomenon of refraction of light to form images.
Concave lens diverge the light incident on it. Hence, called the diverging lens. Due to this these lenses always form diminished, virtual and erect images irrespective of the position of the object in front of them. Thus, the magnification produced by these lenses is always less than one.
Convex lenses converge the light and hence are called the converging lenses. You can observe the magnified image of your palm when the lens is placed close to your palm. This is due the position of the object between the focus and the optic centre. As the object moves away from the lens, the size of its image reduces along with its distance from the lens. Convex lenses form erect, virtual, magnified images or inverted, real, diminished/magnified images depending on the position of the object.
The distance from the principal focus to the optic centre of the lens is the focal length of the lens.
The relation between the focal length (f), object distance (u) and the image distance (v) is given by 1/f = 1/v - 1/u.
All the distances are measured from the optic centre. If we measure the distances in the direction of the incident light, then they are taken positive and else they are taken negative. These constitute the sign conventions.

PROPERTIES OF ETHANOL AND ETHANOIC ACID

THESE VIDEOS CONTAIN THE PROPERTIES OF THE MOST IMPORTANT CARBON COMPOUNDS,THAT ARE

• ETHANOL

• ETHANOIC ACID

REFRACTIVE INDEX

In optics the refractive index or index of refraction n of a substance (optical medium) is a dimensionless number that describes how light, or any other radiation, propagates through that medium. It is defined as

,

where c is the speed of light in vacuum and v is the speed of light in the substance. For example, the refractive index of water is 1.33, meaning that light travels 1.33 times slower in water than it does in vacuum. (See typical values for different materials here.)
The historically first occurrence of the refractive index was in Snell's law of refraction, n₁sinθ₁= n₂sinθ₂, where θ₁ and θ₂ are the angles of incidence of a ray crossing the interface between two media with refractive indices n₁ and n₂.
Refraction, critical angle and reflection of light at the interface between two media.
Brewster's angle, the critical angle for total internal reflection, and the reflectivity of a surface also depend on the refractive index, as described by the Fresnel equations.^[1]
The refractive index can be seen as the factor by which the velocity and the wavelength of the radiation are reduced with respect to their vacuum values: the speed of light in a medium is and similarly the wavelength in that medium is , where is the wavelength of that light in vacuum. This implies that vacuum has a refractive index of 1, and that frequency () of the wave is not affected during refraction. Historically other reference media (e.g., air at a standardized pressure and temperature) have been common.
Refractive index of materials varies with the wavelength. This is called dispersion; it causes the splitting of white light in prisms and rainbows, and chromatic aberration in lenses. In opaque media, the refractive index is a complex number: while the real part describes refraction, the imaginary part accounts for absorption.
The concept of refractive index is widely used within the full electromagnetic spectrum, from x-rays to radio waves. It can also be used with wave phenomena other than light (e.g., sound). In this case the speed of sound is used instead of that of light and a reference medium other than vacuum must be chosen.

CHEMICAL PROPERTIES OF CARBON COMPOUNDS

PART 1




PART 2

Refraction of light.............

Refraction

Refraction is the change in direction of a wave due to a change in its transmission medium.

 

Explanation

 

  An object (in this case a pencil) part immersed in water looks bent due to refraction: the light waves from X change direction and so seem to originate at Y. (More accurately, for any angle of view, Y should be vertically above X, and the pencil should appear shorter, not longer as shown.)  

                                             

In optics, refraction is a phenomenon that often occurs when waves travel from a medium with a given refractive index to a medium with another at an oblique angle. At the boundary between the media, the wave's phase velocity is altered, usually causing a change in direction. Its wavelength increases or decreases but its frequency remains constant. For example, a light ray will refract as it enters and leaves glass, assuming there is a change in refractive index. A ray traveling along the normal (perpendicular to the boundary) will change speed, but not direction. Refraction still occurs in this case. Understanding of this concept led to the invention of lenses and the refracting telescope.

 REFRACTIVE INDEX


In optics the refractive index or index of refraction n of a substance (optical medium) is a dimensionless number that describes how light, or any other radiation, propagates through that medium. It is defined as

,

where c is the speed of light in vacuum and v is the speed of light in the substance. For example, the refractive index of water is 1.33, meaning that light travels 1.33 times slower in water than it does in vacuum. (See typical values for different materials here.)
The historically first occurrence of the refractive index was in Snell's law of refraction, n₁sinθ₁= n₂sinθ₂, where θ₁ and θ₂ are the angles of incidence of a ray crossing the interface between two media with refractive indices n₁ and n₂.

Refraction, critical angle and reflection of light at the interface between two media.