newton rings are observed with the plano convex lens in contact with a glass plate the radius of the first ring is 1 mm if the radius of the convex surface is 4m what is the wavelength of the light used ?
Answers
Answer:
Your answer is given below
Explanation:
There is a phase reversal by reflection at the flat plate.
Constructive interference in the reflected light requires
2t=(m+
2
1
)λ
The first bright ring has m = 0 and the 55th has m = 54, so at the edge of the lens
t=(m+
2
1
)
2
λ
=(54.5)
2
650×10
−9
m=17.7μm
Now from the geometry in textbook figure P37.59, we can find the distance t from the curved surface down to the flat plate by considering distances measured from the center of curvature:
R
2
−r
2
=R−t or R
2
−r
2
=R
2
−2Rt+t
2
Solving for R gives
R=
2t
r
2
+t
2
=
2(1.77×10
−5
m)
(5.00×10
−2
m)
2
+(1.77×10
−5
m)
2
=70.6 m
(b)
f
1
=(n−1)(
R
2
1
−
R
2
1
)=0.520(
∞
1
−
−70.6m
1
) fo f=136 m
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