TITLE INTRODUCTION PRISM AND NATURE OP LIGHT HOW DOES A PRISM WORK? REFRACTION PRISM FORMULA EXPERIMENT BIBLIOGRAPHYINTRODUCTION In optics, a prism is a transparent optical element with flat, polished surfaces that refract light. The exact angles between the surfaces depend on the application. The traditional geometrical shape is that of a triangular prism with a triangular base and rectangular sides,and in colloquial use “prism” usually refers to this type. Some types of optical prism are not in fact in the shape of geometric prisms. Prisms can be made from any material that is transparent to the wavelengths for which they are designed. Typical materials include glass, plastic and fuorite.A prism can be used to break light up into its constituent spectral colors (the colors of the rainbow).Prisms can also be used to refect light, or to split light into components with different polarizations.PRISM AND NATURE OF LIGH Before Isaac Newton, it was believed that white light was colorless, and that the pris itself produced the color. Newton's experiments demonstrated that all the colors already existed in the light in a heterogeneous fashion, and that "corpuscles" (particles) of light were fanned out because particles with different colors traveled with different speeds through the prism. It was only later that Young and Fresnel combined Newton’s particle theory with Huygen’s wave theory to show that color is the visible manifestation of Light's wavelength. Newton arrived at his conclusion by passing the red color from one prism through a second prism and found the color unchanged. From this,he coneluded that the colours must already be present in the incoming light- thus the prism did not create colors, but merely separated colors that are already ther also used a Lens and a second prism to recompose the spectrum back into white Light. This expe: ent has become a classic example of the methodology introduced during the scientif revolution, The results of this experiment dramatically transformed the field of metaphysics, leading to John Loe! primary vs secondary quality distinction. Newton discussed prism dispersion in great detail in his book Opticks. A quantitative introduced in the 1980sHOW DOES A PRISM WORK? Light changes speed as it moves from one medium to another (for example, from air into the glass of the prism). This speed change causes the light to be refracted and to enter the new medium at a different angle (Huygens principle). The degree of bending of the light’'s path depends on the angle that the incident beam of light makes with the surface, and on the ratio between the refractive indices of the two media {Snell's law) The refractive index of many materials (such as glass) varies with the wavelength or color of the Light used, a phenomenon known as dispersion. This causes light of different colors to be refracted differently and to leave the prism at different angles, creating an effect similar to a rainbow. This can be used to separate a beam of white light into its constituent spectrum of colors, Prisms will generally disperse light over a much larger frequency bandwidth than diffraction gratings, making them useful for broad-spectrum spectroscopy. Furthermo: prisms do net suffer from complications arising from overlapping spectral orders, which all ratings have. Prisms are sometimes used for the internal refection at the surfaces rather than for dispersion. If light inside the prism hits one of the sur at a suffciently steep angle, total internal refection occur and all of the light is refected. This makes a prism a useful substitute for a mirror in some situations.Refraction In a homogenous medium, light travels along a straight line. But whenever it falls on the surface of another medium, a very sintl] fraction of it is reflected back and most of the light passes into the medium, though with a change of direction. This phenomenon of the bending of light at the surface of separation of two media is called refrac n of light. Cause of Refraction The phenomenon of refraction takes place when a beam of light enters a medium in which light travels with a different velocity, catig actual pencil pencil seen by viewer Laws Of Reflection: I, The reflected ray, the incident ray, and the normal at the point of incidence all lie in the same plane, 2, The angle of incidence is equal to the angle of reflection,Laws Of Refraction: 1. The incident ray, the refracted ray, and the normal at the point of incidence all lie in the same plane. 2,For any two given media the ratio sin i / sin r is a constant (where i is the angle of incidence, r is the angle of refraction), This is also called Snell's Law. Law of Reflection at Plane Surface A Refractive Index: For a monochromatic light, the ratio of the sine of the angle of incidence to the angle of refraction is a constant for two given media in contact. If "i" is the angle of ineidence and "r" the angle of refraction then sin i / sin r = constant. This constant is called the refractive index. For most purposes it may be assumed that the refractive index is with represet. air, When light travels from rarer to denser medium it bends towards the normal and when it travels from denser to rarer medium it bends away from the normal. It has been experimentally determined that refractive index of a substance,= e/v. e=the speed of light in vacuum v= the speed of Light in the substance Refractive Edge. The line of interaction of the edges of the planes is known as the refractive edge of the prism. Angle of Deviation: The angle through which the incident ray of light is deviated is called the angle of deviation, It is the angle between the emergent ray and the incident ray produced, Angle of Minimum Deviation: As the value of the angle of ineidence (i) increases, the angle of deviation (d) decreases till for a particular value of angle of incidence, it attains a minimum value 'Dm' called the angle of minimum deviation and then increases again. At this angle (0m) the incident ray and the emergent ray are symmetrical w.r.t. the refracting surfaces. Critical Angle: It is that angle of incidence in the denser medium for which the corresponding angle of refraction in the rarer medium is 90 degrees. w= 1/sine , where ht = Refractive Index c= critical angle Relation between refractive index and critical angle according to Snell's Law: bya= sin i/ sin r where i = c and r = 90° baa = sinc/ sin90* = sin c But bya = 1/ apbsin © or apb= I/sin c PRISM FORMULA Let ABC represent a seetion of the glass prism and let L be a ray incident at an angle "I" on the first face AB of the prism at a point "E". NN’ is the normal to this face. The material of the prism is denser with respect to air, as such the ray would refract in the direction making an angle r with the normal, reaching the second face AC of the prism at the point F making an angle ¢ with the normal MM’. The ray emerges in the direction FS bending away from the normal making an angle “e” with the normal. If the incident ray PE be produced forwards to meet FS {also to be produced backwards) at G then the angle HGF is called the angle of deviation and is represented by D. Angle "BAC" is called the refracting angle of the prism and represented by "A" ‘om the figure it can be proved: D= (+e) = (rl + r2) (using exterior angle property of a triangle)A = (rl + 2) Therefore A + D = I * @; whe angle of deviation D has the minimum value Dm, the following conditions are fulfilled 1 =e and rl = r2 =r (say) Applying these conditions in the equation A= 2r Or r = A/2 A+ Dm = 21 T= (A + Dm) /2 Since 1p2 = sin i/ sin r 1p = (sin(A + Dm)/2}/[sin A/2Experiment ATM: To find out the refractive indices of different liquids using a hollow prism and to find the speed of light in given transparent fluids, APPARATUS : * Hollow glass prism * Drawing board Pins Meter scale Protractor Sheets of white paper Various liquids a)Water b) Vinegar c) Vegetable THEORY Light is an electromagnetic radiation that is visible to the human eye usually having a wavelength in the range of 400 nm to 700 nm between the infrared, h longer wavelengths and the ultraviolet with the shorter wavelength. The speed of light in vacuum is found to be exactly 299,792,458 m/s. Observable events that result from the interaction of light and matter are called optical phenomenon. Refraction is a surface phenomenon due to achange in its transmission medium Prism Minimum Deviation Angle Experiment Measure deflection angle through Niquid-filled prism When a ray of light passes from one medium into the other either bends towards the normal or away from the normal in the second medium. This phenomenon is known as the refraction of light. A prism is a transparent optical element with flat, polished surfaces that refract light. Prisms can be made from any material that is transparent including glass, plastic and fluorite. A prism can be used to break light up into its constituent spectral colors. Pris can also be used to reflect Light, or to split light into components with different polarizations. For a particular pair of two media and for a particular wavelength of light (colour) the ratio of the sine of the angle of incidenee and the sine of the angle of refraction is a constant quantity called the refractive index of the second medium w.r.t. the first. It is represented by Qpl = sini / sinr The value of the angle of incidence “i* can be obtained in the terms of the re ing angle "A" of the prism and the angle of minimum deviation "Dm" and the angle of refraction "R" can also be obtained in terms of the refracting angle "A" of the prism. Thus we find that we can use the above relation derived for determining the refractive index. The experiment thus consistsin finding the value of the refracting angle "A" of the prisin and the value of the angle of minimum deviation Dm. The refractive index of the liquid Is given by the formula: uw = (sin(A + Dm) /2}/{sin A/2) r finding the value of Dm a curve is plotted hetween angles of ineidence (i) and their respective angles of deviations (d)., PROCEDURE A) For finding the angle of prism * Take a piece of white paper, fix it on a drawing board using board pins. * Place the hollow glass prism on the sheet and carefully draw its outline, Draw a normal and carefully draw its outline. * Draw a normal and an incident ray at an angle of 35 degrees with the normal on side AB of the prism. * Fix two pins Pl and P2 on the incident ray which are at least 5 cm apart. * Fill the prism with water and place it over its outline. Observe the refracted ray that comes after refraction from the face AB of the prism, * Fix two more pins P3 and P4 to cover the image of Pl and P2. * Obtained angles rl and r2 and add them to obtain the angle of the prism. B) For finding the angle of minimum deviation * Fix a white sheet of paper an a drawing board using board pins * Place a hollow glass prism on the sheet and carefully draw its outline. Draw a normal and an incident ray of angle of incidence 35 degrees on the side AB of the prism* Fix two pins PI and P2 on the incident ray at least 5 cm apart. * Fill the hollow prism with water and place it over its drawn outline, Observe the refracted ray which comes after refraction by placing two more pins P3 and P4 covering Pl and P2. * Extended the incident and refracted ray to obtain the angle of deviation, D, * Repeat the above procedure taking other liquids and the angles of incidence as 40° , 45° , 50° , 55° and 60°. Note the lowest obtained value of angle of deviation as the angle of minimum deviation, Dm . *Using the value of the angle of prism (A) and the angle of minimum deviation (Dm), calculate the value of the refractive index of the liquids by using the equation given in the theory. *Select suitable scales to represent the angle of incidence along the X-axis and angle of deviation along the Y-axis and plot a graph. The graph gives the value of Dm, which is the minimum most point of the parabola. WATERVINEGAR S.No Angle of Incidence [Angle of Deviation 36 26" 40° 25° 45" 23,3" 50" 25° 55° ar 28°VEGETABLE OIL [sae ig 35° 49° OBSERVATIONS : ‘CALCULATIONS : A) Refractive index of Liquids Angle of prism (A) = 60° Formula used: w= {sin ((A + Dm) /2)/(sin €A/2)} Water: Dm=23° Therefore p= sin 41.5 /sin 30 = 0.6626 /0.5 =1. 3252 Vinegar: Dm=23, 5°Therefore p= sin 41.25 /sin 30 = 0.6593 /0. Vegetable Oil: Dm=34* Therefore w = sin 41,25/ sin 30 = 0,6593 /0.6 Liquid gewis) Water ‘S108 13s Vinegar T5108 71 SIR ‘Vegetable oil S108 71636 2OS*108 RESULT The refractive indexes of the four liquids were found to be as follows: * Water, p = 1.3252 * Vinegar, p = 1.3186 * Vegetable Oil, w = 1.4628 The speeds of light in the four liquids were found to be as follows:- * Water, v=2.26x 108 m/s * Vinegar, v=2.27%108 m/s * Vegetable oil, v=2. 05108 m/s PRECAUTIONS* The position of the prism should not be disturbed on the white sheet. * There should be no parallax between the pins Pl, P2 and their images P38, P4. * The angles should be measured carefully. * The curve of the graph should be smooth. SOURCES OF ERROR * Pin pricks may be thick * Measurement of angles may be wrong BIBLIOGRAPHY @ Physics Class XII NCERT Textbook Google images LAB MANNUAL CLASS XI https://wew.quantumstudy.comy e e © vuw.sooste.com e e hutps://mycurvefitcomy