optics (all colleges)-1.pptx

Optics Maysaa. S sulima Ibn Sina University Department of phy Jan ,2023 Intro to Optics The Nature of Light  Before the beginning of the 19th century, light was considered to be a stream of particles.  Then Newton used this particle model to explain reflection and refraction.  In...

Optics Maysaa. S sulima Ibn Sina University Department of phy Jan ,2023 Intro to Optics The Nature of Light  Before the beginning of the 19th century, light was considered to be a stream of particles.  Then Newton used this particle model to explain reflection and refraction.  In 1678, Huygens showed that a wave model of light could also explain reflection and refraction. Intro to Optics The Nature of Light  In 1801, Young provided a demonstration of the wave nature of light, that under appropriate conditions light rays interfere with one another according to the waves in interference model.  Einstein in 1905 explained the photoelectric effect which explains that light consists of particles, called P H O T O NS  Intro to Optics Note that when light strikes a surface, the following four phenomena occur: Reflection (light beam changes direction) Refraction (light beam bends) Scattering (light beam breaks and goes in all directions) Absorption (light is absorbed by a material) THE SPEED OF LIGHT The standard value for the speed of light is 3.00 x 108 m/s and is designated using the lower case letter “c”. RAY OF LIGHT In Geometrical Optics, a ray of light consists of a stream of particles (photons) coming from a light source. Reflection  Mechanism of reflection In specular (regular) reflection each incident ray reflected off in a single direction. A surface that is not shiny creates diffuse reflection. In diffused reflection, a single ray of light scatters into many directions. Law of Reflection 1. The incident ray, the reflected ray, and the normal to the surface all lie in the same plane, 2.The angle of incidence equals the angle of reflection. Refraction  Light rays may bend as they cross a boundary from one material to another, like from air to water.  This bending of light rays is known as refraction.  The light rays from the straw are refracted (or bent) when they cross from water back into air before reaching your eyes. Refraction When a ray of light crosses from one material to another, the amount it bends depends on the difference in index of refraction between the two materials. Refraction  Snell’s law: Snell’s law states that i r e Index of refraction  index of refraction n of a medium to be the ratio Index of refraction The ability of a material to bend rays of light is described by the index of refraction (n). Total Internal Reflection The conditions of total internal reflection: 1) The light should pass from higher optical densed medium to lower densed medium. 2) The incident angle should be greater than the critical angle (c). Total Internal Reflection  (C) is the critical angle for the light to be refracted. Total Internal Reflection . In communications, it is used to transmit telephone, internet, and cable TV signals Total Internal Reflection  Total internal reflection occurs in fiber optics cables. These have applications in: medicine as endoscopes Thin lenses Lenses are commonly used to form images by refraction in optical instruments such as cameras, telescopes, and microscopes.  The distance from the focal point to the lens is called the focal length (𝒇). Thin lenses  Types of lenses: Thin lenses  The thin-lens equation,  From the figure can be used with both magnification can be given converging and diverging by : lenses Thin lenses  The lens-maker’s equation  Where is the focal length of the lens is the radius of curvature of the front surface of the lens is the radius of curvature of the back surface. is the refractive index of the lens is the refractive index of the medium Thin  lenses Three Rules of Refraction for a Convex & concave Lens Thin lenses  Strength of a lens : (power) The reciprocal of the focal length is called the strength of a lens. When the focal length is expressed in meters, the strength has unit of diopters (D):  The effective power:  provided that they are placed close together. DISPERSION AND PRISMS  Dispersion is defined as the spreading of white light into its full spectrum of wavelengths. DISPERSION AND PRISMS  When white light is passed through a glass prism it splits into its spectrum of colors (in order violet, indigo, blue, green, yellow, orange and red). DISPERSION AND PRISMS (A) is the apex angle and (D) is the minimum angle of deviation Primary & Secondary Colors Primary & Secondary Colors Primary color: red, green, and blue (RGB) Secondary colors: The primary colors can be mixed in pairs to form three additional colors red and green light together produce yellow light, blue and green light produce cyan, and red and blue light produce magenta. Human Eye  Eye as an optical system Introduction: Vision is our most important source of information about the external world. It has been estimated that about 70% of a person's sensory input is obtained through the eye. The three components of vision are the stimulus, which is light; the optical components of the eye, which image the light; and the nervous system, which processes and interprets the visual images  Eye as an optical system  Introduction The human eye is roughly a sphere, approximately 2.4 cm in diameter. Light enters the eye through the cornea, which is a transparent section in the outer cover of the eyeball.  Eye as an optical system  introduction The light is focused by the lens system of the eye into an inverted image at the photosensitive retina, which covers the back surface of the eye. Here the light produces nerve impulses that convey information to the brain.  Eye as an optical system  introduction The focusing of the light into an image at the retina is produced by the curved surface of the cornea and by the crystalline lens inside the eye The focus of the crystalline lens, however, is alterable, allowing the eye to view objects over a wide range of distances.  Eye as an optical system Introduction In front of the lens is the iris, which controls the size of the pupil, or entrance aperture into the eye. The front of the eye, between the lens and the cornea, is filled with a watery fluid called the aqueous humour. The space between the lens and the retina is filled with the gelatinous vitreous humour. The cavity of the eye is filled with two types of fluid, both of which have a refractive index about the same as water.  Eye as an optical system introduction The focusing of the eye is controlled by the ciliary muscle, which can change the thickness and curvature of the lens. This process of focusing is called accommodation. When the ciliary muscle is relaxed, the crystalline lens is fairly flat, and the focusing power of the eye is at its minimum.  Eye as an optical system introduction Under these conditions, a parallel beam of light is focused at the retina. Because light from distant objects is nearly parallel, the relaxed eye is focused to view distant objects  Eye as an optical system Focusing and age The near point for a 10-year-old child is about 7 cm, but by the age of 40 the near point shifts to about 22 cm. After that the deterioration is rapid. At age 60, the near point is shifted to about 100 cm. This decrease in the accommodation of the eye with age is called presbyopia  Eye as an optical system Iris – Entrance Aperture of the Eye The iris is the optical aperture of the eye, and its size varies in accordance with the available light. If there is adequate light, the quality of the image is best with the smallest possible aperture.  Eye as an optical system  Focusing The focusing of the light into a real inverted image at the retina is produced by refraction at the cornea and at the crystalline lens. The largest part of the focusing, about two thirds, occurs at the cornea. The power of the crystalline lens is small because its index of refraction is only slightly greater than that of the surrounding fluid.  Eye as an optical system  Light Detection - The Retina The retina consists of photoreceptor cells in contact with a complex network of neurons and nerve fibres which are connected to the brain via the optic nerve. Light absorbed by the photoreceptors produces nerve impulses that travel along the neural network and then through the optic nerve into the brain. Eye as an optical system  Light Detection - The Retina There are two types of photoreceptor cells in the retina: cones and rods. The cones are responsible for sharp color vision in daylight. The rods provide vision in dim light. Near the centre of the retina is a small depression about 0.3 mm in diameter which is called the fovea. It consists entirely of cones. Each cone is about 2μm in diameter. Most detailed vision is obtained on the part of the image that is projected on the fovea. When the eye scans a scene, it projects the region of greatest interest onto the fovea. Eye as an optical system  There are four common defects in vision associated with the focusing system of the eye: 1. myopia (nearsightedness), 2. hyperopia (farsightedness), 3. astigmatism 4. presbyopia (loss of accommodation) The first two of these defects are best explained by examining the imaging of parallel light by the eye.  Eye as an optical system The relaxed normal so called perfect or emmetropic eye focuses parallel light onto the retina.  Eye as an optical system Myopia (nearsightedness) In the myopic eye the lens system focuses the parallel light in front of the retina This mis focusing is usually caused by an elongated eyeball or an excessive curvature of the cornea. Correction with concave lens.  Eye as an optical system  Hyperopia (farsightedness) In hyperopia parallel light is focused behind the retina. The problem here is caused by an eyeball that is shorter than normal or by the inadequate focusing power of the eye. Correction using a convex lens  Eye as an optical system  Astigmatism occurs when either the front surface of the eye (cornea) or the lens inside the eye has mismatched curves. Instead of having one curve like a round ball, the surface is egg-shaped. This causes blurred vision at all distances.  Eye as an optical system Presbyopia: involves a lack of accommodation and is corrected using a bifocal or varifocal lens