To Find The Wavelength of a Sodium Light, By Newton’s Ring.

LIST OF EXPERIMENT 1. To Determine The Value of “g” By Bar Pendulum and Find The Radius of Gyration. 2. To study Moment of Inertia of a flywheel. 3. To Study the Mass Spring System. 4. To Study The Resolving Power of a Telescope. 5. To Find The Wavelength of a Sodium Light, By Newton’s Ring. 6. To Find The Wavelength of a Sodium Light, By Fresnel’s Biprism. 7. To Find The Wavelength of Mercury Green Light By Diffraction Grating using Spectrometer. 8. To Find The Focal Length of Combination of Two Lenses By Nodal Slide Assembly VerifyRotation The Formula. 9. To Find TheAnd Specific of Cane Sugar By Polarimeter. 10. To Find The Dispersive Power of Prism Material Using Polarimeter.

Aim To Find The Wavelength of Sodium Light by Newton’s Ring Method

Apparatus Required Optical arrangement for Newton’s Rings. Travelling microscope. Sodium lamp. Short focus convex lens. Reading lens. Spherometer.

Travelling microscope A travelling microscope is an instrument for measuring length with a resolution typically in the order of 0.01mm .

Different parts of Microscope

Spherometer Spherometer :- It is a precision instrument to measure very small lengths which were primarily used by opticians to measure the curvature of the surface of a lenses

Reading Lenses Reading lenses Magnifying lenses used for good visual correction And Readability.

Newton's rings

Sodium Lamp

THEORY AND FORMULA USED The wavelength of sodium light is given by :Where is the diameter of the (m+p)th ring and is the diameter of the mth ring . R is the radius of curvature of the convex surface of lens and p is a number.

 Hence the determination of involves measurement of radius of curvature of the surface of lens in contact with the plate of the glass and diameter of the two rings, the difference of their number being p

Experimental setup

Setting up of crosswire on newton ring

Procedure Use a short fixed length lens and place it on a plate of glass. The lenses should be placed or mounted on a stand such that the rays fall on the glass plate at 45 to the vertical. The glass plate p was sending the light vertically downwards . Sodium lamp was switched on .

After obtaining bright fringes , set the cross wire at the center of the central dark ring . Use screw to move the cross wire to the twentieth bright ring . Note the readings . Now move the cross wire to nineteenth ring. Repeat it till the cross wire to the twentieth ring on the left hand side . The radius of curvature of lens is obtained with the help of a spherometer.

OBSERVATIONS Least count of vernier calipers = 0.01mm Least count of spherometer = 0.005mm Spherometer readings:h =0.15mm a = 31mm r= 1067.78mm

Observations S. NO.

RING

LEFT READING (MSR + LC x VSR= TSR)

RIGHT READING (MSR + LC x VSR= TSR)

DIAMETE R (MM)

D2 (MM2)

1.

20

51+40x0. 01= 51.40

44+63x0. 01= 44.63

6.77

45.83

2.

19

51+32x0. 01= 51.32

44+81x0. 01= 44.81

6.51

42..38

3.

18

51+16x0. 01= 51.16

44+42x0. 01= 44.42

6.24

38.93

4.

17

51+9x0.0 1 = 51.09

45+9x0.0 1 = 45.09

6.60

36.00

S. NO.

RING

LEFT READING (MSR + LC x VSR= TSR)

RIGHT READING (MSR + LC x VSR= TSR)

DIAMETE R (MM)

D2 (MM2)

7.

14

50+71x0. 01= 50.71

45+49x0. 01= 45.49

5.27

28.83

8.

13

50+57x0. 01= 50.57

45+59x0. 01= 45.59

5.08

25.80

9. 11.

12 10

10. 12.

11 9

50+47x0. 50+22x0. 01= 01= 50.47 50.22 50+33x0. 50+10x0. 01= 01= 50.33 50.10

45+71x0. 4..88 45+81x0. 4..41 01= 01= 45.71 45.81 45+81x0. 4..62 45+94x0. 4..16 01= 01= 45.81 45.94

13.

8

49+93x0. 01= 49.93

46+20x0. 01= 46.20

3.73

23.81 19.44 21.34 12.30

13.91

S.NO.

RING

LEFT READING (MSR + LC x VSR= TSR)

RIGHT DIAMETE D2 READING R (MM2) (MSR + (MM) LC x VSR= TSR)

15.

6

49+57x0. 01= 49.57

46+48x0. 01= 46.48

3.09

9.54

16.

5

49+39x0. 01= 49.39

46+65x0. 01= 46.65

2..74

7.78

17.

4

49+18x0. 01= 49.18

46+86x0. 01= 46.86

2..32

5.38

18.

3

48+93x0. 01= 48.93

47+15x0. 01= 47.15

1.78

3.16

19.

2

48+52x0. 01= 48.52

47+55x0. 01= 47.55

0.97

0.94

CALCULATIONS Taking p = 5, D220 – D215 = 14.36 mm D219 – D214 = 13.55mm D218 – D213 = 13.13mm D217 – D212 = 12.41mm D216 – D211 = 11.80mm D215 – D210 = 12.03mm 10.75mm

D213 – D28 = D212 – D27 = D211 – D26 = D210 – D25 = D 29 – D 24 = D 28 – D 23 =

11.89mm 11.63mm 11.80mm 11.66mm 6.92mm

Mean difference of square of diameter = (14.36 + 13.55 +13.12 +12.41 +11.80 + 11.88 +12.02 + 11.63 + 11.800 +11.66 +6.92 +11.75)/11 =12.38 mm ^(wavelength) =16.20/4*5*106.78 ^ (wavelength)= antilog(log16.20 – log20 – log 1356.64) = 0.0005796615 * 107 A0 = 5796.61 A0

GRAPH

RESULT Wavelength of sodium light calculated by Newton’s rings experiment = 5796.96A 0 :-

= (5796.96-5892)*100/5876.97

= 1.16%

APPLICATIONS OF NEWTON’S RINGS • To measure the refractive index of a substance placed beneath the same lens. • To check the thickness of a surface and to check whether a surface is uniform. • The interference technique of Newton’s rings is widely used for the quality control of optical surfaces because the precision obtained with this method proves to be very satisfactory. The dimensions of the permits calculation of the radii of curvature of the analyzed surfaces and deformation of the interference pattern can be utilized to calculate other parameters such as astigmatism.

1. To check thickness of surface

2. To measure refractive index

3.Interference technique by newton ring experiment.

PRECAUTIONS AND SOURCES OF ERROR • The lens should be of large radius of curvature. • The sources of light used should be an extended one. • Before measuring the diameter of the rings , the range of the microscope should be properly adjusted. • Glass plates and lens should be cleaned thoroughly. • Crosswire should be focused on a bright ring tangentially. • Radius of curvature should be measured accurately.

BIBLIOGRAPHY • • • •

www.google.co.in AK Jha www.wikipedia.org Indu Prakash

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