Dispersive Power of Prism Dispersion Breaking of Light

Dispersive Power of Prism Dispersion: Breaking of Light into its constituent spectral components (ROYGBIV) Prism: 13 June 2021 A prism is a transparent optical element with flat, polished surfaces that refract light. Dr. SCC 1

13 June 2021 Dr. SCC 2

Objective of the experiment: To obtain the dispersive power of material of prism using spectrometer Learning Outcomes( What skills you acquire) • Studying the dispersion effect of prism • Learning to use spectrometer • Determination of dispersive power of material of prism • Understanding the dependence of dispersion on wavelength of light and material. Preparatory Task: • Read the entire script • familiarize yourself with the learning outcomes and skills required • If you are not confident about the above then refer the extra sources to fulfill your desire • Write a short paragraph in your lab book giving details about the experiment , its aim and brief outline about theory behind the experiment. 13 June 2021 Dr. SCC 3

Prism At least two of the flat surfaces must have an angle between them. 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 13 wavelengths for which. Dr. they are designed. Typical materials June 2021 SCC 4 include glass, plastic and fluorite.

Dispersive Power Dispersion occurs because the angle of refraction is dependent on the refractive index of a certain material which in turn is slightly dependent on the wavelength of light that is travelling through it. This means that different wavelengths of light will travel at different speeds, and so the light will disperse into the colours of the visible spectrum, with longer wavelengths (red, yellow) being refracted less than shorter wavelengths (violet, blue). Although the refractive index is dependent on the wavelength in every material, some materials have a much more powerful wavelength dependence (are much more dispersive) than others. Crown glasses such as BK 7 have a relatively small dispersion, while flint glasses have a much stronger dispersion (for visible light) and hence are more suitable for use in dispersive prisms. Fused quartz is used in the ultraviolet as normal glasses lose their transparency there. 13 June 2021 Dr. SCC 5

13 June 2021 Dr. SCC 6

13 June 2021 Dr. SCC 7

EXPERIMENT TITLE AIM : DISPERSIVE POWER OF A PRISM : To determine the dispersive power of material of prism using Spectrometer APPARATUS: Spectrometer, Prism, Mercury Vapor Lamp Spirit Level, Magnifying Glass etc. OBSERVATIONS: i) Least count of Spectrometer : ii) Angle of Prism: 13 June 2021 Dr. SCC 8

Colour Line Used Window Used Spectrometer readings for δ m position a A Direct Position δm = a ~ b Mean δm b δr = Red B A Blue δb = B 13 June 2021 Dr. SCC 9

FORMULA : Dispersive power ( w): - Angular rotation for a given wavelength is called dispersive power of the material of a prism and is given by w = μb - μr / μm - 1 Where μr = sin (A+ δr /2)/sin (A/2) μb = sin (A+ δb /2)/sin (A/2) Calculations: μm = μr + μb / 2 w = μb - μr / μm - 1 13 June 2021 Dr. SCC 10

Precautions : 1. The telescope and collimator should be individually set for parallel rays. 2. Slit should be as narrow as possible. 3. While taking observations, the telescope and prism table should be clamped with the help of clamping screws. 4. Both verniers should be read. 5. The prism should be properly placed on the prism table for the measurement of angle of the prism as well as for the angle of minimum deviation. 13 June 2021 Dr. SCC 11

THEORY: Spectrometer : A spectrometer is used to measure the necessary angles. The spectrometer consists of three units: (1) collimator, (2) telescope, and (3) prism table. The prism table, its base and telescope can be independently moved around their common vertical axis. Schuster’s Method: Setting of Collimator : Setting of Prism Table : Setting of Telescope : Optical Leveling of Prism Table : Obtaining the Spectrum : Finding Angle of Minimum Deviation (δm): 13 June 2021 Dr. SCC 12

Viva Voce (1) What is prism? Ans : A transparent medium like glass bounded by two triangle and three rectangular smooth surfaces (2) Which colour in the spectrum is having maximum and minimum refractive index? Ans : Maximum for Violet Colour Minimum for red colour. (3) What is Refractive index? Ans : The ratio of sine of angle of incidence in the first medium to the sine of angle of refraction in the second medium. (4)What is the function of Collimator? Ans : It will produce parallel beam of light. (5)What do you mean by Angle of Prism? Ans : Angle between two refracting surfaces of the prism. (6)What is Dispersion of Light? Ans : When the light is allowed to fall on one of the refracting surfaces of a prism , it is split into its constituent colours. This splitting of light into its constituent colours by refraction through prism is called Dispersion of light. (7)What is the main optical action of the prism? Ans : The main optical action of a prism is to disperse white light into its component parts. Dispersion of light is minor optical action of prism , but main effect of a prism is to deviate a beam of light. 13 June 2021 Dr. SCC 13

(8) What is Dispersive Power? Ans: Angular rotation for a given wavelength is called dispersive power of the material of a prism (9) What type of material prism is used in this experiment? Ans : Crown / Flint glass prism. (10) What is the unit of Dispersive power? Ans : No unit. (11) What type of light do you use in this experiment? Ans : White light : mercury lamp. 13 June 2021 Dr. SCC 14

IN This Presentation , We learnt……. . • • • What is Dispersion What is prism What is dispersive power of material of prism Schuster’s Method Use of spectrometer Dependence of dispersion 13 June 2021 Dr. SCC 15

13 June 2021 Dr. SCC 16

Dr. SCC 17

13 June 2021 Dr. SCC 18