Tags Physics Isaac Newton Science Experiments

Animals & Plants Arts & Entertainment Auto Beauty & Health Books and Literature Business Electronics Engineering & Technology Food & Drink History Hobbies Jobs & Education Law & Government Math People & Society Science Social Studies Sports Travel & Places

Subjects>Science>General Science

Determination of wavelenght of sodium light using newton rings?

Updated: 4/28/2022

Wiki User

∙ 11y ago

Best Answer

EXPERIMENT: 1

Object: To find the wavelength of Sodium light by Newton's ring.

Apparatus required: A Plano convex lens of large radius of curvature, optical arrangement for

Newton's rings, plane glass plate; sodium lamp and traveling microscope.

Formula used: The wavelength of light is given by the formula

λ =D n

+p -Dn

2 / 4pR

Where D n+p = diameter of (n+p)th ring

Dn = diameter of n th ring,

P = an integer number,

R = radius of curvature of the curved face of the Plano- convex lens.

Procedure:

(1) If a point source is used only then we require a convex lens otherwise while using

an extended source, convex lens L1 is not required.

(2) Before starting the experiment the glass plates G1 and G2 and the plano convex

lens should be thoroughly cleaned.

(3) The centre of lens L2 is well illuminated by adjusting the inclination of glass plate

G1 at 45.

(4) Focus the eyepiece on the cross-wire and move the microscope in the vertical plane

by means of rack and pin on arrangements till the rings are quite distinct. Clamp the

microscope in the vertical side.

(5) According to the theory, the centre of the interference fringes should be dark but

sometimes the centre appears white. This is due to the presence of dust particles

between glass plates G2 and plano-convex lens L2. In this case the lens should be

again cleaned.

(6) Move the microscope in a horizontal direction to one side of the fringes. Fix up the

crosswire tangential to the ring and note this reading. Again the microscope is moved in the

horizontal plane and the cross wire is fixed tangentially to the successive bright fringes noting

the vernier readings till the other side is reached. This is shown in fig. (2)

(7) The radius of curvature of the plano-convex lens is determined by Boy's method as

discussed below:

If an object is placed at the principal focus of convex lens placed over a plane mirror,

its image is formed at same point and the distance from the lens is equal to the focal length

f of the lens as shown in fig. (3i).

If the mirror is removed and the object is moved along the axis, a position will come

where the image of the object formed by the lens coincides with object as shown in fig.

(3ii). If the direction of a ray starting from O is such that it is incident normally on the

spherical surface, the ray returns to its previous path and forms the images at the same

point. Since the refracted ray is normally incident on the surface, it appears to come from the

centre of curvature C. Hence in this case TO=u and TC=v=R we have

Knowing the value of u, the value of R can be calculated because the value of f is already known

with the help of fig. (3i).

The radius of the curvature can also be determined by the using a spherometer. In this case

Where l is the distance between the two legs of the spherometer as shown in fig.(4). H is the

difference of the readings of the spectrometer when it is placed on the lens as well as when

placed on the plane surface.

RESULT: The mean wavelength λ of sodium light = …0 A

Standard mean wavelength λ= …0 A

Percentage Error = …%

SOURCES OF ERROR and PRECAUTION:

(1) Glass plates and lens should be cleaned thoroughly.

(2) The lens used should be of large radius of curvature.

(3) The sources of light used should be an extended one.

(4) Before measuring the diameter of rings, the range of the microscope should be properly

adjusted.

(5) Crosswire should be focused on a bright ring tangentially.

(6) Radius of curvature should be measured accurately.

VIVA- VOCE

Q.1. What is Newton's ring?

Q.2. Why are these rings circular?

Q.3. Why do you an extended source of light here?

Q.4. Why do the rings get closer as the order of the rings increase?

Q.5. On what factors does the diameter of ring depend?

Q.6. Do you get rings in the transmitted light?

Q.7. Why Is the centre of the ring dark?

Q.8. Sometimes the centre is bright. Why?

Q.9. What will happen when the glass plate is silvered on its front surface?

Q.10. What will happen when sodium lamp is replaced by white light source?

Q.11. What will happen if a few drops of a transparent liquid are introduced

between the lens and plate?

Q.12. Why do we make the light fall on the convex lens normally? What will happen

if the light incident obliquely?

Q.13. How can you determine R?

Figure1

Figure 2 Figure 3

OBSERVATION: Value of one division of the main scale=…cm.

No of division on the vernier scale=…

Least count of the microscope = …cm.

Table for determination of (D2

n+p - D2

n) :

No.

The

rings

Micrometer

reading

Diameter

D=(a-b)

cm.

=(a-b)2

cm2

(D2

n+p - D2

cm2

Mean

Cm2

Left

End

a cm.

Right

End

b cm.

….

…

….

…

….

…

….

…

….

…

Table for determination of R:

S.No Position of Position of f. cm Position of

object lens placed

on plane

mirror

lens in

absence of

plane

mirror

u R = uf /f-u

.cm

…

Using spherometer method:

S.No Spherometer Reading

h =(b-a)

cm.

Mean h

cm.

Zero reading on plane

surface

Reading on lens

M.S V.S Total

cm.

M.S V.S Total

cm.

…

(a)

…

(b)

…

Distance between the two legs of spherometer l = …cms.

Calculations:

Using Boy's method:

R = uf /f-u = …cms

Using Spherometer method:

R = (l2 / h ).+ (h / 2)

The wavelength of sodium light is given by:

λ = (D2

n+p - D2

n)/ 4pR = …0 A

The value of (D2

n+p - D2

n) can also be obtained using a graph as shown in fig.(5). The graph is

plotted between the square of diameter of the ring along Y-axis and corresponding number of ring

along X-axis.

Figure 4 Graph

Wiki User

∙ 11y ago

This answer is: