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1-ch.1-1COMPOSSED AND WRITTEN BY PROF. NAJEEB MUGHAL. GOVT. MUSLIM SCIENCE DEGREE COLLEGE HYD. Let’s G¤ To HOUSE OF SUCCESS 1 COME FOR SUCCESS CHAPTER 10 GEOMETRICAL OPTICS Contents: 1. WHAT IS OPTICS? 2. TECHNECAL TERM DEFINITIONS. 3. PATH OF RAYS AND FORMATION OF IMAGE. 4. POSITON AND NATURE OF IMGE. 5. THIN LENS EQUATION AND MAGNIFICATION. 6. MAGNIFYING GLASS AND ITS MAGNIFYING POWER 7. COMPOUND MICROSCOPE. 8. TELESCOPE. AND KIND 9. EYE ANOTOMY 10. EQUATIONS 11. DIMENTIONS 12. SHORT DEFINATIONS 13. SUMMARY 14. SHORT QUESTIONS AND ANSWERS What is OPTICS: Optics is the study of the behavior and properties of light including its interactions with matter and its detection by instruments. Optics usually describes the behavior of visible, ultraviolet, and infrared light. GEOMETRIC OPTICS: In this branch of optics some simple laws are established on the basis of experiments. In this branch light is supposed to travel in straight line path and reflection and refraction of light from materials is studied. PHYSICAL OPTICS: In this branch the production and propagation and emission of light is studied. In this branch, the nature of light and related events like interference, diffraction and polarization are studied. 1: TECHNECHAL TERM RELATIVE DEFINITIONS: i) Ray of light: Light travels in a straight line from a light source. Thus the path of light can be represented by straight line. The direction can be shown by head arrow. The straight line along which the light travels is called ray of light. ii) Beam of light: A light source gives infinite rays of light energy simultaneously. A group of rays which travel along a certain direction is called beam of light. The beam of light can be of the three types: 1) convergent beam: A beam whose all rays go to meet at a point. 2) Divergent beam: If the rays of light starts from appoint and spread away from it. 3) Parallel beam: If all the rays in a beam are parallel to each. iii) Mirror: A mirror is an object with at least one polished and other reflective surface. The most familiar mirror is the plane mirror, which has a flat surface. Curved mirrors are also used, to produce magnified or diminished images or focus light or simply distort the reflected image. The image in a plane mirror is: 1) The same size as the object, 2) The same distance behind the mirror as the object is in front, 3) Laterally inverted, 4) Virtual (it can not be formed on a screen). iv) Lens: A lens is an optical device with perfect axis, which transmits and refracts light, converging or diverging the beam. A spherical transparent medium made of glass or plastic that refracts light waves. Such medium is called “Lens”. The lens can bring light waves together or spread them apart. Hence, there are two types of lenses one of them is called “convex lens”, while the other is “concave lens”. v) Thin lens: It is a lens with a thickness (distance along the optical axis between the two surfaces of the lens) FIRST YEAR Moving 2010 Life Forward 2011 GEOMETRICL OPTICS 1 It’s Understanding, It’s Responsibility, It‘s Desire, It’s Reality, a Better shade, be share ADDRESS: Behind ALFALAH BANK grain Market, Branch, Prince Ali road, Near Sadaf Plaza. Cell# 0333- 2602675 PAGE # 1 CHAPTER # 10 PTCL # 022- 2670019 2-ch.1-1COMPOSSED AND WRITTEN BY PROF. NAJEEB MUGHAL. GOVT. MUSLIM SCIENCE DEGREE COLLEGE HYD. Let’s G¤ To HOUSE OF SUCCESS 2 COME FOR SUCCESS that is negligible compared to the focal length of the lens. Lenses whose thickness is not vi) Convex lens: The lens is thicker at the middle and thinner at the edges. Such lens is called “Convex lens”. A convex lens brings light waves together. This type of lens is also called Double-convex lens. A lens has one side plane while the other convex is called Plano-convex lens. A lens has one side concave while the other convex is called Concavo- convex lens. viI) Concave lens: The lens is thinner in the middle and thicker at the edges. Such lens is called “concave lens”. A concave lens spreads light waves apart. This type of lens is also called Double-concave lens. A lens has one side plane while the other convex is called Planoconcave lens. A lens has one side concave while the other convex is called Convexo- concave lens. viiI) Pole: A mid point of a lens surface is called “pole” or “optical center.” Ix) Principal axis: An imaginary line that passes from a pole of a lens is called principal axis. x) Focus: A single point at which rays of light or other radiation converge or from which they appear to diverge, as after refraction or reflection in an optical system is called the focus of a lens denoted by “ F ”. xi) Focal length: The distance from the focal point of a lens or mirror to the surface of the mirror or the centre of the lens is called “focal length”, denoted by “ f ”. xii) Radius of curvature: f The focal length of lens is half its “radius of curvature, R = . 2 xiii) Object distance: A distance from object placed to pole of a lens, such distance is called “object distance” denoted by “p”. xiv) Image distance: A distance from image formed to pole of a lens, such distance is called “image distance” denoted by “q”. xv) Aperture: In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. xvi) Image: If the rays of light starting from an object after reflection or refraction meet at appoint or appears to come from a point, then this second point miscalled called image point of the first point. Thus the image of each point of the object is formed. The images are of two types: 1)REAL IMAGE :If the rays of light starting from a point after reflection or refraction actually meet at appoint then this point is called the real image point . Such image can be taken on the screen. 2)VIRTUAL IMAGE: If the rays of light starting from a point after reflection or refraction appear to come from second point then this point is called the virtual image of the first point. Such image can not be formed on the screen. FIRST YEAR Moving 2010 Life Forward 2011 GEOMETRICL OPTICS 2 It’s Understanding, It’s Responsibility, It‘s Desire, It’s Reality, a Better shade, be share ADDRESS: Behind ALFALAH BANK grain Market, Branch, Prince Ali road, Near Sadaf Plaza. Cell# 0333- 2602675 PAGE # 2 CHAPTER # 10 PTCL # 022- 2670019 3-ch.1-1COMPOSSED AND WRITTEN BY PROF. NAJEEB MUGHAL. GOVT. MUSLIM SCIENCE DEGREE COLLEGE HYD. Let’s G¤ To HOUSE OF SUCCESS 3 COME FOR SUCCESS xvii) PATH OF RAYS THROUGH CONVEX LENS: 1) Any incident ray traveling parallel to the principal axis of a converging lens will refract through the lens and passes through the focus on the opposite side of the lens. 2) Any incident ray passing through the focus on the way to the lens will refract through the lens and travel parallel to the principal axis. 3)An incident ray which passes through the center of the lens will in effect continue in the same direction that it had when it entered the lens. xviii) FORMATION OF IMAGE THROUGH CONVEX LENS: The image formed by a converging lens can be made using only three principal rays. Suppose an object AB is placed at a distance “p” from a pole of convex lens. According to the ray rules, the rays from the object point A, are converge at a point A’; such point is called image point. Hence, we get complete image A’B’ of an object, at a distance “q” from a pole of converging lens. xix) POSITION AND NATURE OF IMAGE THROUGH CONVEX LENS: 1) Suppose an object is at infinity or (p=), its image will be located at focus(q=f). The nature of image will be real, inverted and very small in size. 2) Suppose an object is away from 2F or (p2f), its image will be located away from F or (2f<q<f). The nature of image will be real, inverted and small in size. 3) Suppose an object is on to 2F or (p= 2f), its image will be located at 2F or (q=2f).The nature of image will be real, inverted and equal in size. Hence, p=q=2f. 4) Suppose an object is between 2F and F or (f<p<2f), its image will be located away from 2For (q2f).The nature of image will be real, inverted and large in size. 5) Suppose an object is on to F (p=f), its image will be real, inverted and very large in size located at infinity or (q=). 6) Suppose an object is between focus and pole of lens (p f), its image will be located to the same side of object. The nature of image will be virtual, erect and magnified. Hence a convex lens is called “diverging lens”, or simple microscope or magnifying glass. xx): PATH OF RAYS THROUGH CONCAVE LENS: 1) If an incident ray is passing from a focus, after refraction it diverges and appears to come parallel to principal axis. 2) If an incident is parallel to principal axis, after refraction it diverges and appears to come from focus. 3) If an incident ray is passing from a pole of lens; it passes away with out refraction. xxi):FORMATION OF IMAGE THROUGH CONCAVE LEARNS: The image formed by a diverging lens can be made using only three principal rays: Suppose an object AB is placed in front of concave lens at a distance “p” from its pole. According to ray rules the rays from a point A diverge after refraction and appears to come from a point A’, such point is called “image point”. Hence, we get image A’B’ at a distance “q” from a pole. xxiii) POSITION AND NATURE OF IMAGE THROUGH CONCAVE LENS: Suppose an object is placed anywhere on to principal axis of concave lens. Its image always located between focus and pole of lens, to the same side of object placed. The nature o f image will be always virtual, erect and diminished. FIRST YEAR Moving 2010 Life Forward 2011 GEOMETRICL OPTICS 3 It’s Understanding, It’s Responsibility, It‘s Desire, It’s Reality, a Better shade, be share ADDRESS: Behind ALFALAH BANK grain Market, Branch, Prince Ali road, Near Sadaf Plaza. Cell# 0333- 2602675 PAGE # 3 CHAPTER # 10 PTCL # 022- 2670019 4-ch.1-1COMPOSSED AND WRITTEN BY PROF. NAJEEB MUGHAL. GOVT. MUSLIM SCIENCE DEGREE COLLEGE HYD. Let’s G¤ To HOUSE OF SUCCESS 4 COME FOR SUCCESS DESCRIPTIVE PART 2: THIN LENS EQUATION: The combined relation between object Distance (p), image distance (q) and focal length (f), is called “thin lens Equation”. i) Convex lens equation: Let us consider an object OÓ high is placed between 2F and F at a distance “p” apart, from pole of a convex lens. Its real and inverted image Iľ high is to be located at a distance “q”, away from 2F. Consider OPO’ and ŀPI’ right-angled triangles .Both triangles are similar. Therefore, Tan P = OO' OP And Tan P = II' IP By comparing, we get, OO' II' = OP IP IP II' = OP OO' q II' - - - - - - - eq.(1) = p OO' Consider PFE and IFI’ right angled triangles. Both triangles are similar FP Tan F = PE FI Tan F = And II' FP FI = By comparing, we get, PE II' II' FI = - - - - - - - eq.(a) PE FP From the fig., OO’ = PE, FP = f and Fŀ = q – f II' q-f = Therefore - - - - - - - eq.(2) OO' f q (q-f) By comparing equation #s 1 and 2, we get, = p f qf=P(q–f) qf=pq– pf Divide both sides by p q f, we get, qf p qf = pq pq f - pf p q f 1 1 1 1 1 1 = = + This equation is called “ convex lens equation”. p f q f p q FIRST YEAR Moving 2010 Life Forward 2011 GEOMETRICL OPTICS 4 It’s Understanding, It’s Responsibility, It‘s Desire, It’s Reality, a Better shade, be share ADDRESS: Behind ALFALAH BANK grain Market, Branch, Prince Ali road, Near Sadaf Plaza. Cell# 0333- 2602675 PAGE # 4 CHAPTER # 10 PTCL # 022- 2670019 5-ch.1-1COMPOSSED AND WRITTEN BY PROF. NAJEEB MUGHAL. GOVT. MUSLIM SCIENCE DEGREE COLLEGE HYD. Let’s G¤ To HOUSE OF SUCCESS 5 COME FOR SUCCESS ii)Concave lens equation: Let us consider an object OÓ high is placed between 2F and F at a distance “p” apart, from pole of a convex lens. Its real and inverted image Iľ high is to be located at a distance “q”, away from 2F. Consider OPO’ and ŀPI’ right-angled triangles .Both triangles are similar. OO' Tan P = Therefore, OP And Tan P = By comparing, we get, II' IP OO' II' = OP IP IP II' = OP OO' q II' - - - - - - - eq.(1) = p OO' Consider PFE and IFI’ right angled triangles. Both triangles are similar Therefore, FP Tan F = PE FI Tan F = And II' FP FI = By comparing, we get, PE II' II' FI = - - - - - - - eq.(a) PE FP From the fig., OO’ = PE, FP = f and FI = ( f – q ) f - q - - - - - - - - eq.(2) II' Therefore, = OO' f f - q q By comparing equation #s 1 and 2, we get, = p f qf=p(f–q) qf=pf–pq qf Pf pq Divide by p q f, both sides we get, = pqf pqf pqf qf p qf = pf p q f - pq pq f 1 1 1 = p q f 1 1 1 This equation is called “concave lens equation”. - =p p f NOTE: 1) The object distance is positive, for real objects, and negative for virtual objects. 2) The image distance is positive for real images and negative for virtual images. 3) The focal length is positive for convex lens and negative for concave lens. FIRST YEAR Moving 2010 Life Forward 2011 GEOMETRICL OPTICS 5 It’s Understanding, It’s Responsibility, It‘s Desire, It’s Reality, a Better shade, be share ADDRESS: Behind ALFALAH BANK grain Market, Branch, Prince Ali road, Near Sadaf Plaza. Cell# 0333- 2602675 PAGE # 5 CHAPTER # 10 PTCL # 022- 2670019 6-ch.1-1COMPOSSED AND WRITTEN BY PROF. NAJEEB MUGHAL. GOVT. MUSLIM SCIENCE DEGREE COLLEGE HYD. Let’s G¤ To HOUSE OF SUCCESS 6 COME FOR SUCCESS 3 :MAGNIFICATION: Magnification is the process of enlarging something only in appearance, not in physical size. This enlargement is quantified by a calculated number also called magnification. When this number is less than one it refers to a reduction in size, sometimes called magnification. Mathematically it is, “The ratio between sizes of image to the size of object”. size of image ( Hi ) Magnification = size of object ( H o ) H q Mag: = i = Ho p 4: MAGNIFYING GLASS: The simple converging lens is called “Magnifying glass”. It is used to see small objects enlarge. How large an object appears, depends on the size of the image, it makes on the retina of an eye. This depends on the angle subtended by the object at the eye. As an object bring up close to our eyes so that it subtended a greater angle. However, our eyes can accommodate only up to a standard distance of 250 mm called “least distance of distinct vision” denoted by “d”. The converging lens when acts as the magnifying glass then virtual image, which must be at least 25 cm from an eye, if the eye is to focus on it. Magnifying power: “The ratio of the angle subtended by a object when using the lens (), to the angle subtended using the eye () with an object at least distance of distinct vision”. β Magnifying power = α Magnifying power of magnifying glass: A convex lens is called “magnifying glass”, when object is placed in the range of focal length. 1 1 1 We know that , = + , only for convex lens. f p q 1 1 1 for virtual image, in convex lens as diverging lens. = f p q 1 1 1 for magnifying glass. = f p d multiply both sides by “d”. d d d = f p d d d = -1 f p d d f + 1 = p d M.P.= + 1 f 5:COMBINATION OF LENSES: When two or more lenses are combined this is way to design an optical instrument and to increase the magnifying power. A light passes through several lenses; the image formed by one lens becomes the object for the next lens. Total magnification will be the product of the separate magnification of each lens. Suppose an abject PQ is placed at a distance p1 apart from first lens. It’s real inverted image P’Q’ is located at q1 , determined by lens equation, FIRST YEAR Moving 2010 Life Forward 2011 GEOMETRICL OPTICS 6 It’s Understanding, It’s Responsibility, It‘s Desire, It’s Reality, a Better shade, be share ADDRESS: Behind ALFALAH BANK grain Market, Branch, Prince Ali road, Near Sadaf Plaza. Cell# 0333- 2602675 PAGE # 6 CHAPTER # 10 PTCL # 022- 2670019 7-ch.1-1COMPOSSED AND WRITTEN BY PROF. NAJEEB MUGHAL. GOVT. MUSLIM SCIENCE DEGREE COLLEGE HYD. Let’s G¤ To HOUSE OF SUCCESS 7 COME FOR SUCCESS 1 1 1 = + f1 p1 q1 The second lens is placed at L distance apart from the first. Thus L= ( q1 + p2 ).The final image P’’Q’’ located through second lens will be at a distance q2 apart, which can be determined from, 1 1 1 = + f2 p2 q 2 Where p2 = ( L- q1) and f1 , f2 are the focal lengths of first and second lens respectively. Now suppose two lenses are placed in close contact the separation between them is negligible or less than their focal lengths. A point object O is placed at p from the first lens of focal length f1 .Its real point image l located across the second lens at q1 , which can be determined by 1 1 1 = + - - - - - - - eq.(1) f1 p q1 This real point image becomes virtual object for the second lens; there is zero separation between the lenses. Hence q1 = - p2.The final point image ľ is located at a distance q from the second lens determined by, 1 1 1 = + f2 p2 q 2 1 1 1 =+ ------------- eq. (2) f2 q1 q Add equation #s I and 2, We get, 1 1 1 1 1 1 + = + + + f1 f 2 p q1 q1 q 1 1 1 1 + = + f1 f 2 p q 1 1 1 + = If, f1 f 2 f 1 1 1 = + Then, f p q This shows that two lenses act as the single lens have “f” focal length. 6:POWER OF LENS: The reciprocal of focal length of a lens is called “power of lens” expressed in meter. 1 Power of lens = f It’s unit is “diopter” expressed in meter. Shorter the foal length, greater the power of lens. 7: POWER ACCOMMODATION: The ability of an eye to change the focal length of its lens so as to from a clear image of an object on its retina is called its “power accommodation”. 8:DEFECTS OF LENS: Chromatic aberration: The dispersion of light into its constituent colors gives rise a blurred image, which appears colored. This defect in the image is called “Chromatic aberration”. A lens acts like two prisms placed end to end. This gives rise to dispersion of light. Chromatic aberration can be removed by using a compound lens consisting of a convex lens of one type of glass and concave lens of FIRST YEAR Moving 2010 Life Forward 2011 GEOMETRICL OPTICS 7 It’s Understanding, It’s Responsibility, It‘s Desire, It’s Reality, a Better shade, be share ADDRESS: Behind ALFALAH BANK grain Market, Branch, Prince Ali road, Near Sadaf Plaza. Cell# 0333- 2602675 PAGE # 7 CHAPTER # 10 PTCL # 022- 2670019 8-ch.1-1COMPOSSED AND WRITTEN BY PROF. NAJEEB MUGHAL. GOVT. MUSLIM SCIENCE DEGREE COLLEGE HYD. Let’s G¤ To HOUSE OF SUCCESS 8 COME FOR SUCCESS dispersion. The convex lens produces both deviation and dispersion. The concave lens minimized the deviation and neutralizes completely the dispersion. . Such a combination of lenses is called “Achromatic lens” (color corrected lens). Spherical aberration: The rays, which pass through a lens near its edges, are brought to focus closer to the lens as compared to the central rays. The image produced will not be well defined and sharp. This defect in a lens is called “Spherical aberration”. This defect can be removed by using only the central portion of the lens. A lens system that is corrected spherical aberration, chromatic aberration and other an “Astigmatic lens”, whish is used in costly cameras and other optical distortion is called instruments. 9:COMPOUND MICROSCOPE: Introduction: optical instrument used to increase the apparent size of an object It has multiple magnification. The compound microscope was invented by Galileo in 1610 . The lenses with shortest focal length gives the greatest magnification and small objects are seen enlarged. Construction: It consisted of an objective lens and an eyepiece. The objective of microscope is of smaller focal length f o and eyepiece has a greater focal length fe than the objective (fo< fe ). Both lenses are kept at the two ends of tube. Working: A very small in size object is placed between the focus and twice the distance of the focal length of objective, say very close to the focal length p1 fo . This lens forms an inverted, magnified real image in front of eyepiece. The eyepiece is so adjusted that it forms a virtual magnified image of already inverted image, say L q2. The eyepiece acts as the magnifying glass. Magnification of compound microscope: A compound microscope consists two converging lenses, so that it has multiple magnifying power. Hence, M.P. = (M.P)o ( M. P. )e q q M.P.= 1 2 p1 o p 2 e L d M.P. = 1+ fe fo , because eye piece acts as the magnifying glass. As larger the focal length of objective than, the smaller focal length of eyepiece, the magnification will becomes very shorter. 10 : TELESCOPE: Introduction: A telescope is a device used to magnify distant objects. An object, which is far away, viewed by an optical instrument, known as “Telescope”. The function of a telescope is to increase the visual angle which a distant object appears to subtend at the eye and therefore produces the same effect as if the object were either larger or close to the eye. A Telescope is used to magnify objects that are very far away. Construction: A Telescope is used to magnify objects that are very far away. It contains two converging lens located at opposite ends of a long tube. The lens closest to the object is called the “objective” and a lens close to an eye is called “eyepiece”, which acts as a magnifier. FIRST YEAR Moving 2010 Life Forward 2011 GEOMETRICL OPTICS 8 It’s Understanding, It’s Responsibility, It‘s Desire, It’s Reality, a Better shade, be share ADDRESS: Behind ALFALAH BANK grain Market, Branch, Prince Ali road, Near Sadaf Plaza. Cell# 0333- 2602675 PAGE # 8 CHAPTER # 10 PTCL # 022- 2670019 9-ch.1-1COMPOSSED AND WRITTEN BY PROF. NAJEEB MUGHAL. GOVT. MUSLIM SCIENCE DEGREE COLLEGE HYD. Let’s G¤ To HOUSE OF SUCCESS 9 COME FOR SUCCESS There are number of kinds of telescope, some of them are: Astronomical telescope, reflecting telescope, radio telescope, Galilean telescope, terrestrial telescope. Astronomical Telescope: An astronomical telescope used to see distant objects like stars, planets, moon etc., which is effectively at infinity. In refracting astronomical telescopes two convex lenses are used. In this telescope only those rays from the object, which are bounded by the edges of the objective lens enter the instrument. The lens acts as a stop to the light from the object with a given objective, the best position of the eye is one where it collects as much light as possible from that passing through the objective. Working: A converging lens of larger focal length, which is used as the objective lens fo .It will form the image of a distant object at infinity as close to the eye as we may desire. The image II’ is real. Another converging lens of smaller focal length f e ( f o >f e ) used as the eye piece near the image formed by objective. The image I and focal planes of both lenses are in conjunction and the light coming out from the eyepiece is parallel. The final virtual, erect and very large in size image Iľ is at infinity by viewing eye. Thus, the distance between two lenses is (fo+fe) for an object at infinity. Magnification of Telescope: The magnifying power of a telescope is defined as the ratio between the angle subtended at the eye ( ) by the final image and the angle subtended at eye ( ) by the object itself . β Magnifying power = α α= β= Size of image OI focal length of objective q1 Size of image OI focal length of eyepiece p 2 Because, f o q1 Because, fe p2 OI fe Magnifying power = OI fo focal length of objective f o Magnifying power = focal length of eye piece f e For Greater magnification, the objective have larger focal length and the eyepiece a shorter one. 11:GALILEAN TELESCOPE: The scientist Galileo invented this optical instrument. The concave lens serves as the ocular lens, or the eyepiece of small focal length of small focal length, while the convex lens serves as the objective of large focal length and eyepiece. The lens are situated on either side of a tube such that the focal point of the ocular lens is the same as the focal point for the objective lens. The rays of light from a very distinct object fall parallel making a small visual angle with the axis of the objective and an inverted image is formed in its focal length plane. But before he image is formed the eyepiece diverges the rays. The position of he concave lens is so adjusted that the image is within the focal length and therefore the virtual and enlarged image of the object is formed have larger visual angle .The final image is upright with respect to object. β Thus, Magnifying power = α FIRST YEAR Moving 2010 Life Forward 2011 GEOMETRICL OPTICS 9 It’s Understanding, It’s Responsibility, It‘s Desire, It’s Reality, a Better shade, be share ADDRESS: Behind ALFALAH BANK grain Market, Branch, Prince Ali road, Near Sadaf Plaza. Cell# 0333- 2602675 PAGE # 9 CHAPTER # 10 PTCL # 022- 2670019 10-ch.1-1COMPOSSED AND WRITTEN BY PROF. NAJEEB MUGHAL. GOVT. MUSLIM SCIENCE DEGREE COLLEGE HYD. Let’s G¤ To HOUSE OF SUCCESS 10 COME FOR SUCCESS 12: TERRESTRIAL TELESCOPE: The construction and working of this telescope is same as the astronomical telescope. But the only difference is that erecting lens of smaller focal length is introduced between the objective and eyepiece. The objective forms a real inverted image of distinct object, at its focus. This image is situated at distance twice the focal length of erecting lens. Thus this lens forms inverted and real image at the same distance to the other side of erecting lens. Thus final image is upright with respect to object. This image is formed with the focal length of eyepiece, which forms its enlarged and virtual image. 13:ANATOMY OF THE EYE: The human eye resembles cameras in its structure. The eye is an enclosed volume into which light passes through a lens. A diaphragm, called the “Iris” (the colored part of an eye), adjusts automatically to control the amount of light entering the eye. The hole in the iris through which light passes (the pupil) is black because no light is reflected from it and very little light is reflected back out from the interior of the eye. The Retina, which plays the role of the film in camera, is on the curved rear surface. It consists of a complex array of nerves and receptors known as rods and cons, which act to change light energy into electrical signals that travel along the nerves. The reconstruction of the image from all these tiny receptors is done mainly the brain. At the center of the retina is a small area called the Fovea, about bo.25 mm in diameter, where the cones are very closely packed and the sharpest image and best color discrimination are found. Unlike a camera, the eye contains no shutter. The equivalent operation is carried out by the nervous system, which analyses the signals to form image at the rate of about 30 per second. The lens of the eye does little of the bending of light rays. Most of the refraction is done at the front of the cornea (index of refraction = 1.376), which acts as a protective covering. The lens acts as a fine adjustment for focusing at different distances. This is accomplished by the capillary muscles, which change the curvature of the lens so that the focal length is changed. To focus on distant objects, the muscles are relaxed and the lens is thin. When light from a distant object passes through the lens system of the eye it is refracted and brought to focus on he retina. There a real but inverted image of the objects formed. While all retinal images are inverted, they are interpreted as being erect. To focus on nearby objects the muscles contact, causing the center of the lens to be thicker, thus shortening the focal length. This focusing adjustment is called accommodation. The closest distance at which the eye can focus clearly is called the near point of the eye .For young and adult it is 25cm .A person’s far point is the farthest distance at which n object can be seen clearly. For some purposes I is useful to speak of a normal eye and far point of infinity. The important optical features of an eye are: 1. The Eye –lens, which focuses light entering the eye. 2. The Ciliary muscles, which are attached to the eye lens surface and alter the focal length. 3. The Retina, the light sensitive area of calls at the back of the eye. 4. The Yellow spot (fovea centralism), the most light sensitive spot on the retina 5. The Iris, the spot colored circle round the eye lens. 6. The Pupil, the circular opening or diaphragm in the iris through which light passes. 7. The Cornea, the thick transparent protective covering in front of the eye lens. It refracts the light most 8. The Aqueous humor and Vitreous humor, which are liquids respectively in front of and behind the eye lens in which the eye lens is suspended. FIRST YEAR Moving 2010 Life Forward 2011 GEOMETRICL OPTICS 10 It’s Understanding, It’s Responsibility, It‘s Desire, It’s Reality, a Better shade, be share ADDRESS: Behind ALFALAH BANK grain Market, Branch, Prince Ali road, Near Sadaf Plaza. Cell# 0333- 2602675 PAGE # 10 CHAPTER # 10 PTCL # 022- 2670019 11-ch.1-1COMPOSSED AND WRITTEN BY PROF. NAJEEB MUGHAL. GOVT. MUSLIM SCIENCE DEGREE COLLEGE HYD. Let’s G¤ To HOUSE OF SUCCESS 11 COME FOR SUCCESS 14:DEFECTS OF EYE: The defects of vision are due to the inability of the eye lens to produce sharp images at the retina. The two main defects of vision are: I) Shortsightedness (Myopia) II) Long-sightedness ( Hypermetropia) Short sighted (Myopia): Some people cannot see long distance objects clearly without spectacles. This defect of vision is called “myopia or short sighted ness It is due to the eyeball being too large. Light rays from distant objects are focused in front of the retina and a blurred image is produced. Short sight can be corrected by placing suitable concave lens in front of the eye. Light rays from the distant objects are now diverging by this lens before entering the eye. Light rays appear to come from a distant point forming a sharp image. Long sighted (Hyper metropia): The disability of eye to form distinct images of nearby objects on its retina is known as Hyper metropia Equations. 1 1 1 1 L d 1 1 1 d 3. Power = 1. 2. 4. M.P. = 1+ 5. M.P of M.G = 1+ f f f1 f 2 f p q fo fe f q q f 6 Magnifying power of compound microscope = 1 2 7. magnifying power of telescope = o fe p1 o p2 e 8.Length = ( q + p ) 9. Length of telescope = f e + fo 10. angular magnifying power = β d 11. linear magnifying power = α p Dimensions. QUANTITY FORMULA Object distance = image distance = focal length = p = q = f Magnifying power = magnification Length of telescope 1 Power of lens f DIMENSION [L] dimensionless [L] [L-1] UNIT meter no unit meter meter-1 = Diopter Short questions Q. # 1: Why should the magnifying lens placed close to the eye? Answer: Because, the virtual, erect and enlarged image located at least distance of distinct vision by using magnifying glass. So that, to see clear object, the magnifying lens is placed close to an eye. Q. # 2: Why should the objective of compound microscope have small focal length? Answer: Because, an object should placed be very closer to the focus of objective to get real, large and inverted image formed close to the pole of eyepiece. Hence, the objectives of compound microscopes have smaller focal length Q. # 3: Under what condition a double convex lens acts as a diverging lens? FIRST YEAR Moving 2010 Life Forward 2011 GEOMETRICL OPTICS 11 It’s Understanding, It’s Responsibility, It‘s Desire, It’s Reality, a Better shade, be share ADDRESS: Behind ALFALAH BANK grain Market, Branch, Prince Ali road, Near Sadaf Plaza. Cell# 0333- 2602675 PAGE # 11 CHAPTER # 10 PTCL # 022- 2670019 12-ch.1-1COMPOSSED AND WRITTEN BY PROF. NAJEEB MUGHAL. GOVT. MUSLIM SCIENCE DEGREE COLLEGE HYD. Let’s G¤ To HOUSE OF SUCCESS 12 COME FOR SUCCESS Answer: The condition under which double convex lens acts as a diverging lens is when an object is placed with in the focal length say object distance less than focal length, then double convex lens is called diverging lens. Q. # 4: Why is convex lens of small focal length preferred for a magnifying glass? Answer: Because, a lens having smaller focal length, greater magnifying power. We know d according equation that, Magnification = 1 + . Hence, convex lens of small focal length f preferred for a magnifying glass Q. # 5: Distinguish between telescope and compound microscope. Answer: Telescope: 1. It is used to see far away objects. 2. It is used to see objects; whose visual angle is very small 3. The final image at least distance of distinct vision or at infinity 4. The image formed by objective is small and real. 5. The focal length of objective is larger than eyepiece 6. The final image should be smaller than object but visual angle increases 7. The eyepiece cannot act as the magnifying glass. 8. The length of instrument is fo + fe. 9. The magnifying power is fo / fe . compound microscope 1. It is used to see close objects. 2. It is used to see small. 3. The final mage will be at least distance of distinct vision. 4. The image formed by objective large and real. 5. The focal length of objective is smaller than eyepiece 6. The final image should be virtual erect and magnified. 7. Eyepiece act as the magnifying glass 8. The length of instruments q1 + p2 9. The magnifying power is (M.P.)o (M.P.)e Q. # 6: How can a real image be distinguished from a virtual image? Answer: Real image: Virtual image: 1. It can be projected on to screen. 1. It cannot project on to screen. 2. It is always inverted. 2. It is always erect. 3. This type of image is formed by the actual interaction of reflected or refracted light rays 3. This type of image is formed by not actual interaction of reflected or refracted rays. Q. # 7: Explain why the lenses used in expensive optical devices are composed of more than one part? Answer: The lenses used in the expensive devices are composed of more than one part only to remove lens defects. The results should be correct. Q. # 8: Why the magnifying lens should placed close to the eye? Answer: Because, the virtual, erect and magnified image should be located at least distance of distinct vision. So that, the magnifying lens should placed close to the eye Q. # 9: When light enters glass from air, its speed becomes less. Is it due to change in frequency or wavelength? Answer: FIRST YEAR Moving 2010 Life Forward 2011 GEOMETRICL OPTICS 12 It’s Understanding, It’s Responsibility, It‘s Desire, It’s Reality, a Better shade, be share ADDRESS: Behind ALFALAH BANK grain Market, Branch, Prince Ali road, Near Sadaf Plaza. Cell# 0333- 2602675 PAGE # 12 CHAPTER # 10 PTCL # 022- 2670019 13-ch.1-1COMPOSSED AND WRITTEN BY PROF. NAJEEB MUGHAL. GOVT. MUSLIM SCIENCE DEGREE COLLEGE HYD. Let’s G¤ To HOUSE OF SUCCESS 13 COME FOR SUCCESS The speed of light in a medium depends on its wavelength. The decrease of speed is due to decrease of wave length. Q. # 10: An object is placed with in the focal length of convex lens. What will be the nature of image? Answer: When an object is placed with in the focal length of convex lens then the nature of image will be virtual erect and magnified. Q. #11: What is the difference between Galilean telescope and astronomical telescope? Answer: Galilean telescope: Astronomical telescope: 1. In this telescope concave lens is used as the eyepiece. 1. In this type of telescope convex lens is used as eyepiece. 2. in this telescope erect final image formed 2. In this telescope inverted final image formed Q. # 12: Define visual angle? Answer: The visual angle is the angle subtended between an object and an eye or image and magnifying glass. Q. # 13: Explain linear magnification? Answer: The ratio between the sizes of image to the size of object is called linear magnification. height of image Magnification = height of object Q. # 14: What are the defects of lenses? Answer: There are two defects of lenses i) spherical ii) and chromatic aberration. Q. # 15: Where will be the image formed, if an object is placed between F and 2F of convex lens? Answer: When an object is placed between F and 2F then the image will be formed away from 2F. The nature of image will be real, inverted and large in size. Q. # 16: Why should the eyepiece of telescope have small focal length? Answer: The eyepiece of telescope is used of smaller focal length. Because, in the telescope, object is placed for away from the focus of objective. Its real and small image formed close to the focus of eyepiece. The final image should be enlarged and virtual has larger visual angle. To get higher magnification have eyepiece of telescope have smaller focal length eyepiece of telescope have small focal length. Q. #17: What is least distance of distinct vision? Answer: The minimum distance to see an object clearly is 25cm called “least distance of distinct vision”. Q. #18: Why we combine two or more than two lenses? Answer: Two or more lenses are combined to design an optical instrument. By this combination the power of lens also increases. By this process, we avoid lens defects. Q. # 19: What is power of convex lens, whose focal length is 20cm? Answer: We know that, 1 power = f 1 Power= 20cm FIRST YEAR Moving 2010 Life Forward 2011 GEOMETRICL OPTICS 13 It’s Understanding, It’s Responsibility, It‘s Desire, It’s Reality, a Better shade, be share ADDRESS: Behind ALFALAH BANK grain Market, Branch, Prince Ali road, Near Sadaf Plaza. Cell# 0333- 2602675 PAGE # 13 CHAPTER # 10 PTCL # 022- 2670019 14-ch.1-1COMPOSSED AND WRITTEN BY PROF. NAJEEB MUGHAL. GOVT. MUSLIM SCIENCE DEGREE COLLEGE HYD. Let’s G¤ To HOUSE OF SUCCESS 14 COME FOR SUCCESS 100 .Thus Power = 5 Diopter 20 meter Q. #20: What Is the Power Of Accommodation of the Eye? Answer: Accommodation in the eye is the process by which the eye increases optical power to maintain a clear image on the retina. The focus of the eye is controlled by a number of factors including the iris, cornea, and muscle tissue that alters the shape of the lens so that the eye can focus on both near and far objects. Sometimes these muscles don't work properly because the eye is slightly altered in shape, and as people age, the lens becomes harder and cannot be properly focused leading to poor vision. If the point of focus is short of the retina, it's known as "nearsightedness" which means that the eye cannot focus on distant objects. "Farsightedness" is where people have problems focusing on nearby objects Q. # 21: can you see stars by a compound microscope. Answer: No, it is not possible that e can see the stars by compound microscope. Because, eyepiece is of larger focal length than the objective. So this is not possible. Q. # 22: what do you understand by the power of lens? Write its unit obtains formula for the power of two lenses placed in contact. Answer: The reciprocal of focal length is called power of lens expressed in Diopter. 1 Power of lens = f The unit of power of lens is Diopter expressed in m-1. When two or more lenses are used in close combination, that is, with no space in between them, the equation to 1 1 1 + + +- - - - calculate the effective power of the combination is: Powercombination = f1 f2 f3 Q. # 23: Why is a candle flame yellow? Answer: The received color of an object is determined by the spectrum of its radiant flux factored by the luminous efficacy of the human eye .If the human eye responded equally to all wavelengths in the visible range; the candle flame would appear red. But since the eye sensitivity peaks in the green and diminishes toward the red wavelengths, the eye perceives the color as yellow. Q. # 24: why a pin hole placed in front of a lens leads to a good image even when the image is not quit in focus. Answer: A pin hole placed in front of a lens reduces its aperture. The image is formed by the central rays. Thus we obtain a good image even of the lens is not in focus. Q. # 25: what happens when light hits the object? Answer: When a light wave hits an object, what happens to it depends on the energy of the light wave, the natural frequency at which electrons vibrate in the material and the strength with which the atoms in the material hold on to their electrons. Based on these three factors, four different things can happen when light hits an object: The waves can be reflected or scattered off the object. The waves can be absorbed by the object. The waves can be refracted through the object. The waves can pass through the object with no effect. And more than one of these possibilities can happen at once. Q. # 26: Why sky seem to be blue? Power = FIRST YEAR Moving 2010 Life Forward 2011 GEOMETRICL OPTICS 14 It’s Understanding, It’s Responsibility, It‘s Desire, It’s Reality, a Better shade, be share ADDRESS: Behind ALFALAH BANK grain Market, Branch, Prince Ali road, Near Sadaf Plaza. Cell# 0333- 2602675 PAGE # 14 CHAPTER # 10 PTCL # 022- 2670019 15-ch.1-1COMPOSSED AND WRITTEN BY PROF. NAJEEB MUGHAL. GOVT. MUSLIM SCIENCE DEGREE COLLEGE HYD. Let’s G¤ To HOUSE OF SUCCESS 15 COME FOR SUCCESS Answer: Because, atmosphere is containing molecules of many different sizes, including nitrogen, oxygen, water vapor and various pollutants so that the Earth's atmosphere is rough. This assortment scatters the higher energy light waves, the ones we see as blue light. This is why the sky looks blue. Q. # 27: Why focal length of convex lens is more for red colour light? Answer: Because, when light possesses from convex lens it bends to wads the normal. This coloured light has larger wave length smaller frequency. So that focal length of convex lens is more. Q. #28: Two thin lenses are in contact. Now they are separated and placed coaxially. What will be the power of lens combination? Answer: When two thin lenses are in contact the power of lens combination increases. Now when they are separated and placed coaxially the power of lens combination decreases. Q. # 29: Why does sunlight drain colour? Answer: The sunlight (electromagnetic radiation) chemically breaks down dyes. Washing detergents and bleach do the same thing. The exact chemical formula of the dyes will make a difference in how long the color lasts but, nothing lasts forever. Sunlight carries ultraviolet (UV) light along with visual spectrum light. The UV light causes a chemical reaction with color molecules and they fade over time. FIRST YEAR Moving 2010 Life Forward 2011 GEOMETRICL OPTICS 15 It’s Understanding, It’s Responsibility, It‘s Desire, It’s Reality, a Better shade, be share ADDRESS: Behind ALFALAH BANK grain Market, Branch, Prince Ali road, Near Sadaf Plaza. Cell# 0333- 2602675 PAGE # 15 CHAPTER # 10 PTCL # 022- 2670019 16-ch.1-1COMPOSSED AND WRITTEN BY PROF. NAJEEB MUGHAL. GOVT. MUSLIM SCIENCE DEGREE COLLEGE HYD. Let’s G¤ To HOUSE OF SUCCESS 16 COME FOR SUCCESS Q. # 21: What is the use of spectrometer? Answer: Q. # 22: What are the defects of vision? How can these be corrected? Answer: We know Q. # 32: How is the magnifying power of a a) telescope b) compound microscope, affected by increasing the focal length of their objective Answer: Q. # 32: Define in short the construction working and magnifying power of a compound microscope? Answer: Q. # 32: Show how the position nature and size of the image are formed by a) convex lens b) concave lens. Answer: Q. # 32: show that a real image of a man formed by a converging lens only inverts him but that he and his image still have the same right hand. Answer: Q. # 32:if a telescope is focused on a moon and then directed towards a tree 50m away , what adjustment would be necessary to focus the tree sharply/ Answer: Q. # 32: what wavelength of light would you recommended for use with a microscope if the maximum detail was to be seen. Answer: The wavelength of light doesn't limit magnification. It limits resolution. You can have magnifications that go far beyond the limits of resolution. In that situation, things would look larger, but you would not see any more detail. Two factors limit resolution in a light microscope. The wavelength of light and the Numerical Aperture of the lens system. The shortest visible wavelength is ~400 nm. The highest Numerical Aperture for a lens system to date is 1.4. This means the best resolving power on a microscope is ~200 nm. Q. # 32: what are the different arrangements used for decreasing the length of terrestrial telescope. Answer: Q. # 32: What is an image? Answer: In optics, the likeness or counterpart of an object produced when rays of light coming from that object are reflected from a mirror or are refracted by a lens Q. # 32: What is a virtual image? Answer: On the other hand, a virtual image occurs when the prolongations of the light rays converge to form an image, but the light rays themselves do not reach the point of convergence. Q. # 32: What is a real image? Answer: A real image occurs when the rays of light from the object actually converge to form an image and can be seen on a screen placed at the point of convergence FIRST YEAR Moving 2010 Life Forward 2011 GEOMETRICL OPTICS 16 It’s Understanding, It’s Responsibility, It‘s Desire, It’s Reality, a Better shade, be share ADDRESS: Behind ALFALAH BANK grain Market, Branch, Prince Ali road, Near Sadaf Plaza. Cell# 0333- 2602675 PAGE # 16 CHAPTER # 10 PTCL # 022- 2670019 17-ch.1-1COMPOSSED AND WRITTEN BY PROF. NAJEEB MUGHAL. GOVT. MUSLIM SCIENCE DEGREE COLLEGE HYD. Let’s G¤ To HOUSE OF SUCCESS 17 COME FOR SUCCESS FIRST YEAR Moving 2010 Life Forward 2011 GEOMETRICL OPTICS 17 It’s Understanding, It’s Responsibility, It‘s Desire, It’s Reality, a Better shade, be share ADDRESS: Behind ALFALAH BANK grain Market, Branch, Prince Ali road, Near Sadaf Plaza. Cell# 0333- 2602675 PAGE # 17 CHAPTER # 10 PTCL # 022- 2670019 18-ch.1-1COMPOSSED AND WRITTEN BY PROF. NAJEEB MUGHAL. GOVT. MUSLIM SCIENCE DEGREE COLLEGE HYD. Let’s G¤ To HOUSE OF SUCCESS 18 COME FOR SUCCESS FIRST YEAR Moving 2010 Life Forward 2011 GEOMETRICL OPTICS 18 It’s Understanding, It’s Responsibility, It‘s Desire, It’s Reality, a Better shade, be share ADDRESS: Behind ALFALAH BANK grain Market, Branch, Prince Ali road, Near Sadaf Plaza. Cell# 0333- 2602675 PAGE # 18 CHAPTER # 10 PTCL # 022- 2670019