Refraction and Prism

AIM:
i)To investigate the dependence, of the angle of deviation on the angle of incidence, using a hollow prism filled one by one with different transparent fluids. ii)And find the speed of light in given transparent fluids.

APPARATUS REQUIRED:
Drawing board, white sheets of paper, hollow prism, different liquids(water, kerosene, oil, spirit etc) drawing pins, pencil, half metre scale, thumb pins,graph papers and a protractor.

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 fluorite. 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 reflect light, or to split light into components with different polarizations.

PRISM AND NATURE OF LIGHT:
Before Isaac Newton, it was believed that white light was colorless, and that the prism 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 Huygens’ 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 concluded that the colors must already be present in the incoming light — thus, the prism did not create colors, but merely separated colors that are already there. He also used a lens and a second prism to recompose the spectrum back into white light.

This experiment has become a classic example of the methodology introduced during the scientific revolution. The results of this experiment dramatically transformed the field of metaphysics, leading to John Locke’s primary vs secondary quality distinction. Newton discussed prism dispersion in great detail in his book Opticks.[1] He also introduced the use of more than one prism to control dispersion.[2] Newton’s description of his experiments on prism dispersion was qualitative, and is quite readable. A quantitative were introduced in the 1980s.[3]

THEORY:
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. Furthermore, prisms do not suffer from complications arising from overlapping spectral orders, which all gratings have. Prisms are sometimes used for the internal reflection at the surfaces rather than for dispersion. If light inside the prism hits one of the surfaces at a sufficiently steep angle, total internal reflection occurs and all of the light is reflected. This makes a prism a useful substitute for a mirror in some situations.

A triangular prism, dispersing light; waves shown to illustrate the differing wavelengths of light.

Angle of Minimum Deviation:
A) Defination: The minimum value of angle of deviation, is called angle of minimum deviation. It is represented by the symbol Dm.

b) Explanation: For same angle of deviation (D) there are two values of angle of incidence. One value equals ’i’ and other value equals ‘e’ As angle ‘i’ is increased from a small value, ‘e’ decreases from large value and angle of deviation decreases. When angle of deviation is minimum(Dm), then, ‘i’ and ‘e’ becomes equal.

DIAGRAMS:

Which of these images should we take for the project..???

TYPES OF PRISM:
Dispersive prisms

Comparison of the spectra obtained from a diffraction grating by diffraction (1), and a prism by refraction (2). Longer wavelengths (red) are diffracted more, but refracted less than shorter wavelengths (violet). Main article: Dispersive prism

Dispersive prisms are used to break up light into its constituent spectral colors because the refractive index depends on frequency; the white light entering the prism is a mixture of different frequencies, each of which gets bent slightly differently. Blue light is slowed down more than red light and will therefore be bent more than red light.

OBSERVATIONS:
As given in the practical book on page no.256

CALCULATIONS:
What should we do in the calculations…?? Should we go according to the formula given in the book..??

GRAPHS:
Graph between angle of incidence and angle of deviation.

RESULT:

1.The i-D graph indicates that as the angle of incidence(i) increases, the angle of deviation(D)nfirst decreases, attains a minimum value (Dm) and then again start increasing for further increase in angle of incidence. 2.The angle of minimum deviation for a)water Dm= o

b)kerosene or glycerine Dm= c)spirit Dm=

d)turpentine oil Dm=

3.The refractive indices of the a) water n= b)kerosene or glycerine n= c) spirit n= d) turpentine oil n= 4.Speed of light a) water v= m/s m/s

b) kerosene or glycerine v= c) spirit v= m/s d) turpentine oil v= m/s

DOUBTS:
Ma’am can we use glycerine instead of kerosene and the rest liquids are oil, spirit and water… And anything else that we should include in the project…??? Is any more information required for the project or this is enough..???