Determination of wavelength of sodium light newton's rings. readings__
Answers
Answer:
Aim : To determine the wavelength of sodium light by Newton's ring. ... Formula used : The wavelength λ of light is given by the formula: Where, Dn+m = diameter of (n+m)th ring, Dn = diameter of nth ring, m = an integer number (of the rings) R = radius of curvature of the curved face of the plano-convex lens.
Answer:
The experiment is given for the Determination of wavelength of sodium light newton's rings
Explanation:
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 n2+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.
