In a Newton's rings pattern the dark ring due to 7000 A° of any order is found to
coincide with the dark ring due to 5000 Aº of the next order. If the radius of curvature
of the lens is 148.8 cm find the diameter of the overlapping dark rings.
[ Ans. :0.5 cm]
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Answer:
Diameter of the 20th dark ring.
D
20
=5.8 mm=5.82×10
−3
m
Radius of the 20th dark ring
r
20
=2.91×10
−3
m
Diameter of the 10th dark ring
D
10
=3.36 mm=3.36×10
−3
m
Radius of the 10th dark ring
r
10
=1.68×10
−3
m
Radius of plano-convex lens (R)=1 m
Wavelength of light
=
mR
r
n+m
2
−r
n
2
=
10×1
[(2.91×10
−3
)
2
−(1.68×10
−3
)
2
]
=
10
[8.4681−2.8224]×10
−6
=0.5646×10
−6
=5636
A
o
.
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