Final Lab report report on Snell\'s law PDF

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complete lab report on Snell's law including experimental verification of this law using glass slab experiment...

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NameSubjectDateCollege nameSubmitted toFinal lab report Title: Refraction through glass slab experiment and verification of Snell’s law. Abstract: The graph-1 shows a linear relationship; the greater the angle of incidence, the greater the angle of refraction. Although the refractive indices of all angles were nearly identical, I regret not trying more angles to see if this would have altered the refractive index. Nonetheless, I was able to achieve my goal since I was able to calculate the refractive index from this experiment using Snell's Law. The values can be rounded to a refractive index of 1.5 for all angles which is a constant according to Snell’s Law. The experiment has also proven that light bends/refracts when it enters a different medium. Measuring the accuracy of angles was a bit hard because if the mark was between one degree, it could have ranged anywhere from 0.1-0.9 degrees but I had to round it to 0.5 degrees. I also need to plot error bars the next time I draw a graph. I chose the thinnest beam but still it was rather thick, which made it difficult to determine the exact point at which the light entered the medium. Marking the exact point of the light beams, parallax errors, and determining where to draw the point are all areas where there are uncertainties. However, the results were quite accurate as it falls in close proximity to the expected result found in references.

INTRODUCTION Light moves at certain speeds. However, when the speed changes, it causes the light to bend, the bending of light is called refraction which is quite apparent in everyday life. Dispersion through prism, twinkling of stars, sun dog effect or the illusion of multiple sun are all the examples of this phenomenon. Glass is a perfect everyday example of light refraction. If a slab of glass is placed over a piece of paper, then the words will look closer to the surface because of the different angle the light is bending. The bending causes the light ray to refract at some angle, this is how Snell's law came into effect. The law is used in ray tracing to compute the angles of incidence or refraction, and in experimental optics to find the refractive index. In this experiment we can determine the bending of light rays owing to the change in refractive index and hence verifying the law. In optics, Snell's law describes the link between the route travelled by a beam of light as it crosses the boundary or separation surface between two interacting substances and their respective refractive indices. Willebrordus Snellius, a Dutch astronomer and mathematician, developed this law in 1621(also called Snellius). The account of Snell's law remained unpublished until Christiaan Huygens mentioned it in his dissertation on light. SNELL’S LAW. The ratio of the sine of angle of incidence to the sine of angle of refraction is a constant quantity for the two media.

Only isotropic or specular media are subject to Snell's law (such as glass). Birefringence in anisotropic media, such as certain crystals, can split the refracted beam into two rays: the ordinary or o-ray, which follows Snell's law, and the extraordinary or e-beam, which is not always coplanar with the incident beam. Snell's law has numerous applications in physics, particularly in the field of optics e.g. optical fiber. It's found in things like eyeglasses, contact lenses, cameras, and rainbows. The refractive index of liquids is calculated using Snell's law by a device called a refractometer. It's frequently utilized in the candy-making sector. Hypothesis: we predicted that the difference in the refractive index of the media will cause bending of light and also predicted that the angle of incidence would be directly proportional to the angle of refraction. Objective: To study Refraction through glass slab experiment and verification of Snell's Law.

METHODS Materials Required:        

One drawing board or cardboard (A4) all pins white sheet of paper(A4) A rectangular glass slab protractor measuring scale(30cm) pencil 6-8 thumb pins.

Theory: SOME IMPORTANT TERMS: Normal Ray: A ray of light which forms an angle of 90° with the refracting surface is said to be normal. When a ray of light travels along the normal, it does not suffer any refraction. Incident Ray: A ray of light that travels towards the refracting surface is called incident ray. Refracted Ray: A ray of light that changes its path when passes through a refracting surface is said to be refracted ray. Emergent Ray: A ray of light which emerges out into the original medium after refraction is said to be an emergent ray. Lateral Displacement: The perpendicular shift in the path of light, seen when it emerges out from the refracting medium is called lateral displacement. Angle of Incidence (i): The angle formed between the normal and incident ray is called angle of incidence.

Angle of Refraction (r): The angle formed between the refracted and normal ray is called angle of refraction. Angle of Emergence (e): The angle formed between the normal and emergent ray is called angle of emergence. During Refraction: (i) Angle of incidence = Angle of emergence. (ii) Incident ray and emergent ray are parallel. VARIABLES INVOLVED: Constant variable- refractive index of glass, position of glass slab, the colour of light ray. Independent variable- angle of incidence(i) of the light ray nor al to the glass slab. Dependant variable- angle of refraction(r) of the light ray normal to the glass slab.

Experimental set-up: In order to maximize the relative intensity of the light ray, it is required to turn off the lights and close the curtains and the same glass slab should be used through the experiment to ascertain constant refractive index. White plain sheet is used to ensure the clarity of observations. During the projection of light ray, it is needed to make sure that the ray is always at the centre of and parallel to the respective radial line so that the angle made by ray to the normal is same as that by the radial line.

PROCEDURE: 1. A sheet of white paper was fixed on the cardboard with the help of the pins and the glass slab was placed in the middle of the sheet. 2. The boundary of the slab was marked with a sharp pencil and was labelled as ABCD once the slab glass slab was removed. 3. On the line AB mark a point E and draw a normal at it. A line is drawn making an angle i with the normal, the angle should be neither too small nor too large. 4. The slab was again placed on the boundary ABCD and two pins were fixed vertically about 3-4 cm apart on the line AE. 5. Looked through the glass slab along the plane of paper from the CD side and head was moved until the images of the two pins were seen clearly. Closing one eye, the position is adjusted such that the images of the pins lie in the same straight line. 6. Other two pins were fixed vertically such that the images of all the four pins lie in the same straight line. 7. The slab and the pins were removed and points were encircled with the help of pencil. 8. The points were joined and produced towards the slab so that it meets the boundary line CD. Thus, the incident ray, refracted ray and emergent ray was obtained respectively. 9. The angles were measure with the help of the protractor and labelled as < i , < r and < e. 10. The process was repeated for different angles of incidence i to get a verified result.

OBSERVATION AND RESULTS: TABLE 1- EXPERIMENTAL DATA (taking the value of angle up to one decimal places) S.n o

CALCULATION:

1

Angle of incidence(i) {In degrees} 10

Angle of refraction(r) {In degrees} 6.5

2

20

13

3

30

19.5

4

40

25

5

50

31

6

60

35

For

7

70

39

i=10 degrees

8

80

39.5

r=6.5 degrees Sin(i)=0.173 sin(r)=0.113 n=sin(i)/sin(r) n=0.173/0.113

n= 1.53 (calculated value of refractive index from the experimental data) Similarly for the rest of the values of i and r we can calculate the value of n.

Average value = (sum of all he values of n)/number of n values = (1.53+1.52+1.49+1.52+1.48+1.51+1.49+1.54)/8 =1.52

TABLE 2- CALCULATED VALUES s.no

Sin(i)

Sin(r)

n=sin(i)/sin(r)

1

0.173

0.113

1.53

2

0.342

0.224

1.52

3

0.500

0.334

1.49

4

0.642

0.422

1.52

5

0.766

0.515

1.48

6

0.866

0.573

1.51

7

0.939

0.629

1.49

8

0.984

0.636

1.54

Average(n)

1.51

sin(i) vs sin(r) 0.7 0.6

sin(i)

0.5 0.4 0.3 0.2 0.1 0 0.1

0.2

0.3

0.4

0.5

0.6

sin(r)

0.7

0.8

0.9

1

1.1

GRAPH-1

Slope of the above graph will give the value of n

Slope =sin(i)/sin(r)=n n=refractive index of glass slab       

Here calculated slope from the graph= 1.513 Greater the angle of incidence results in greater the angle of refraction (maximum value of angle of incidence...