Physics project

,

using hollow prism filled, one by one,

with different transparent fluids.

NAME: NEHA GUPTA

CLASS: 12-A

ROLL NO:

AIM

,

using hollow prism filled, one by one,

with different transparent fluids.

CERTIFICATEThis is to certify that the Project titled 'hollow prism' was completed under my guidance and supervision by Roll No. ________ a student of XII-A SCI, Bal Bhavan public school within the stipulated time as prescribed by MS.NITIKA KHANDELWAL.

ACKNOWLEDGEMNT

I gratefully acknowledge my sincere thanks to our respected PHYSICS teacher MS.NITIKA KHANDELWAL for her remarkable, valuable guidance and supervision throughout the project work. I'm very thankful for her encouragement, help, suggestion and readily helpful service in performing the experiment.

Neha Gupta Roll NO :

INDEX

IntroductionIn optics, a prism is a transparent optical element with flat, polished surfaces that refract light . 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 wavelengths for which they are designed. Typical

materials include glass, plastic and fluorite.

A dispersive prism can be used to break light up into its constituent spectral colors (the colors of

the rainbow). Furthermore, prisms can be used to reflect light, or to split light into components with

different polarizations.

HOW PRISMS WORK

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

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

constituentspectrum 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.

THEORY

DISPERSION OF LIGHT BY PRISM

In the Light and Color unit of The Physics Classroom Tutorial, the visible light spectrum was introduced and discussed. Visible light, also known as white light, consists of a collection of component colors. These colors are often observed as light passes through a triangular prism. Upon passage through the prism, the white light is separated into its component colors - red, orange, yellow, green, blue and violet. The separation of visible light into its different colors is known as dispersion. It was mentioned in the Light and Color unit that each color is characteristic of a distinct wave frequency; and different frequencies of light waves will bend varying amounts upon passage through a prism. In this unit, we will investigate the dispersion of light in more detail, pondering the reasons why different frequencies of light bend or refract different amounts when passing through the prism.

Earlier in this unit, the concept of optical density was introduced. Different materials are distinguished from each other by their different optical densities. The optical density is simply a measure of the tendency of a material to slow down light as it travels through it. As mentioned earlier, a light wave traveling through a transparent material interacts with the atoms of that material. When a light wave impinges upon an atom of the material, it is absorbed by that atom. The absorbed energy causes the electrons in the atom to vibrate. If the frequency of the light wave does not match the resonance frequency of the vibrating electrons, then the light will be reemitted by the atom at the same frequency at which it impinged upon it. The light wave then travels through the interatomic vacuum towards the next atom of the material. Once it impinges upon the next atom, the process of absorption and re-emission is repeated. 

 

The optical density of a material is the result of the tendency of the atoms of a material to maintain the absorbed energy of the light wave in the form of vibrating electrons before reemitting it as a new electromagnetic disturbance. Thus, while a light wave travels through a vacuum at a speed of c (3.00 x 108m/s), it travels through a transparent material at speeds less than c. The index of refraction value (n) provides a quantitative expression of the optical density of a given medium. Materials with higher index of refraction values have a tendency to hold onto the absorbed light energy for greater lengths of time before reemitting it to the interatomic void. The more closely that the frequency of the light wave matches the resonant frequency of the electrons of the atoms of a material, the greater the optical density and the greater the index of refraction. A light wave would be slowed down to a greater extent when passing through such a material

What was not mentioned earlier in this unit is that the index of refraction values are dependent upon the frequency of light. For visible light, the n value does not show a large variation with frequency, but nonetheless it shows a variation. For instance for some types of glass, the n value for frequencies of violet light is 1.53; and the n value for frequencies of red light is 1.51. The absorption and re-emission process causes the higher frequency (lower wavelength) violet light to travel slower through crown glass than the lower frequency (higher wavelength) red light. It is this difference in n value for the varying frequencies (and wavelengths) that causes the dispersion of light by a triangular prism. Violet light, being slowed down to a greater extent by the absorption and re-emission process, refracts more than red light. Upon entry of white light at the first boundary of a triangular prism, there will be a slight separation of the white light into the component colors of the spectrum. Upon exiting the triangular prism at the second boundary, the separation becomes even greater and ROYGBIV is observed in its splendor.

 

 

THE ANGLE OF DEVIATION

The amount of overall refraction caused by the passage of a light ray through a prism is often expressed in terms of the angle of deviation ( ). The angle of deviation is the angle made between the incident ray of light entering the first face of the prism and the refracted ray that emerges from the second face of the prism. Because of the different indices of refraction for the different wavelengths of visible light, the angle of deviation varies with wavelength. Colors of the visible light spectrum that have shorter wavelengths (BIV) will deviated more from their original path than the colors with longer wavelengths (ROY). The emergence of different colors of light from a triangular prism at different angles leads an observer to see the component colors of visible light separated from each other.

 

Of course the discussion of the dispersion of light by triangular prisms begs the following question: Why doesn't a square or rectangular prism cause the dispersion of a narrow beam of white light? The short answer is that it does. The long answer is provided in the following discussion and illustrated by the diagram below.

Suppose that a flashlight could be covered with black paper with a slit across it so as to create a beam of white light. And suppose that the beam of white light with its component colors unseparated were directed at an angle towards the surface of a rectangular glass prism. As would be expected, the light would refract towards the normal upon entering the glass and away from the normal upon exiting the glass. But since the violet light has a shorter wavelength, it would refract more than the longer wavelength red light. The refraction of light at the entry location into the rectangular glass prism would cause a little separation of the white light. However, upon exiting the glass prism, the refraction takes place in the opposite direction. The light refracts away from the normal, with the violet light bending a bit more than the red light. Unlike the passage through the triangular prism with non-parallel sides, there is no overall angle of deviation for the various colors of white light. Both the red and the violet components of light are traveling in the same direction as they were traveling before entry into the prism. There

is however a thin red fringe present on one end of the beam and thin violet fringe present on the opposite side of the beam. This fringe is evidence of dispersion. Because there is a different angle of deviation of the various components of white light after transmission across the first boundary, the violet is separated ever so slightly from the red. Upon transmission across the second boundary, the direction of refraction is reversed; yet because the violet light has traveled further downward when passing through the rectangle it is the primary color present in the lower edge of the beam. The same can be said for red light on the upper edge of the beam.

 

Dispersion of light provides evidence for the existence of a spectrum of wavelengths present in visible light. It is also the basis for understanding the formation of rainbows.

PRISM

A prism is a portion of a transparent medium bounded by two plane faces inclined to each other at a

suitable angle.

Angle A between the two refracting surfaces ABQP and APRC is called the angle of prism.

A ray of light suffers two refractions on passing through a prism.If KL be a monochromatic light falling on

the side AB, it gets refracted and travels along LM. It once again suffers a refraction at M and emerges

out along MN. The angle through which the emergent ray deviates from the direction of incident ray is

called angle of deviation 'd'

Sub Topics

1. Relation between Refractive index (m) Angle of Prism (A) and angle of deviation (d)

 

RELATION BETWEEN REFRACTIVE INDEX (M) ANGLE OF PRISM (A) AND ANGLE OF DEVIATION (D)Back to Top

Draw LO and MO at L and M respectively. Extend KL and MN to meet at P.

 

 

i.e. d = i1 r1 + i2 r2

d = i1 + i2 (r1 + r2)

(exterior angle is sum of interior opposite angles)

In the quadrilateral ALOM

(From Snell's law)

As the angle of incidence is increased, angle of deviation 'd' decreases and reaches minimum value. If

the angle of incidence is further increased, the angle of deviation is increased. Let dm be the angle of

minimum deviation. The refracted ray in the prism in that case will be parallel to the base.

 

 

For minimum deviation position the incident ray and emergent rays are symmetrical with respect to the

refracting surface and LM is parallel to BC.

i1 = i2 = i

and r1 = r2 = r

2r1 = A , r1= A/2

dm = 2i1 - 2r1

dm = 2i1 - A

or 2i1 = dm + A

From Snell's Law

This is the Prism formula when the prism is in the minimum deviation position.

Apparatus required

• Disposable plastic spoons • Thermometer • Three shallow plates or saucers • Oven • Electronic

kitchen balance (accurate to 0.1 g)

Chemicals required

Distilled water • Metric liquid measuring cup (or graduated cylinder) • Three clean glass jars or

beakers • Non-iodized table salt (NaCl) • Epsom salts (MgSO4) • Sugar (sucrose, C1 2 H 2)

Procedure

1.Measure 100 mL of distilled water and pour into a clean, empty beaker or jar.

2. Use the kitchen balance to weigh out the suggested amount (see below) of the solute to be tested. a. 50 g Non-iodized table salt (NaCl) b. 50 g Epsom salts (MgSO4) c. 250 g Sugar (sucrose, C12H22O11)

3. Add a small amount of the solute to the water and stir with a clean disposable spoon until dissolved.

4. Repeat this process, always adding a small amount until the solute will no longer dissolve.

5. Weigh the amount of solute remaining to determine how much was added to the solution.

6. Try and add more solute at the same temperature and observe changes if any.

7. Now heat the solutions and add more solute to the solutions.

Observations

Salt Amount of salt dissolved in 100mL water tO make saturated solution.

Moles dissolved

NaCl (Non-iodized common salt) =

36.8 grams 0.7

MgSO4 32.7 grams 0.255

C12H22O11 (sucrose) 51.3 grams 0.15

Adding more solute at the same temperature to the saturated solutions yielded no significant changes in NaCl and Epsom salt. Howerver at

all temperatures the saturation point of sucrose could not be obtained exactly as due to the large size of the molecule the solution became thick and refraction was more prominent. Neglecting this observation in the room for error, the experiments agreed with the theory. Adding more solute to heated solutions increased the solubility in all the 3 cases. The largest incrrease was shown by NaCl, followed by Epsom salt and sucrose. These facts too agreed with the theory as at high temperatures the kinetic enery of molecules increases and the collisions are more effective.

Conclusions

The solubility of NaCl is the highest as it an ionic salt and easily dissociates in water. Also since the size of both the cation and anion are small, the collisions are more and hence probability of dissociation is high. The solubility of MgSO4 is also high as it is also an ionic salt, but due to a larger anion, collisions are not very effective. The solubility of C12H22O11 is the least as it a very large molecule due to which hydrogen bonding with the water molecules is not very effective. Also due to the large number of carbon and oxygen atoms, inter molecular H-bonding is more dominant than intramolecular H-bonding.

Precautions

1. While adding the solute to the solvent, the solution should be stirred slowly so as to avoid the

formation of any globules.

2. Stirring should not be vigorous as the kinetic energy of the molecules might change due to

which solubility can increase.

3. While stirring, contact with the walls of the container should be avoided as with every collision, an impulse is generated which makes the dissolved solute particles rearrange themselves. As a result

solubility can decrease.

4. The temperature while conducting all the three experiments should be approximately same.

5. Epsom salt should be first dried in order to remove the water of crystallization (MgSO4.7H2O).

Result

The saturated solutions of NaCl, MgSO4 and C12H22O11 were made and observed. The observations agreed with the related theory within the range of experimental error.

Bibliography

1. https://www.google.co.in

2. www.icbse.com

3. https://www.wikipedia.org

4. chemistry practical book (Comprehensive)

5. http://www.tcyonline.com