3.12.4 Experimental procedures
1)Adjustment of the apparatus
(1)Turn on the sodium lamp to make it glow.
(2)Adjust the angle of the glass to 45° gradually for the strongest reflected light in Newton’s rings until the uniform and bright yellow light field is observed through the eyepiece of the microscope.
(3)Adjust gradually the eyepiece and focal distance of reading microscope to make the cross and interference fringes clear.
2)Measurement of the diameters Dm and Dn of rings
(1)Move Newton’s rings slightly to make the cross point and the center of Newton’s rings coincide roughly,and turn the cross of the eyepiece to make it parallel to the reading stable.Turn the reading drum to make the cross move left to the 25th ring around,then turn to the k=20 ring reversely and make the cross tangent to the outer of the ring while recording the data.In the following,turn the reading drum in the same direction to make the cross tangent to the outer of the k=19,18,17,16,15,14,13,12,11 ring fringes successively,and record the corresponding reading of the ring fringes.Continue turning the reading drum in the same direction to make the cross move over the central spot and then tangent again to the outer of the k=11,12,13,14,15,16,17,18,19,20 ring fringes located at the right side of the central spot successively,then record the reading data.
(2)According to the following formula,we can calculate the diameter of the Newton’s rings:
(https://www.daowen.com)
3)Repeat the steps
Repeat the steps above for several times,and calculate the respective average diameters
of the ring fringes.
4)Tips and Attentions
(1)During the same measurement,the reading drum is turned towards the same direction to avoid the deviation caused by the screw clearance.Don’t turn the reading drum reversely.
(2)Adjust the tube slowly from bottom to top during focusing to avoid destroying the objective lens and the undetected objects.
(3)Avoid misreading the ordinal of the two sides of interference rings.Be careful to record the reading during turning the reading drum.
(4)Don’t turn on and off the sodium lamp alternately,or it will age too early.
