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Combination of Lenses
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Two plano convex lenses of focal lengths
Question
Two plano convex lenses of focal lengths
f
1
β
and
f
2
β
set for minimising spherical aberration are kept apart by 2 cm. If the equivalent focal length of combination is 10 cm, the values of
f
1
β
and
f
2
β
are :
A
1
8
c
m
,
1
6
c
m
B
1
8
c
m
,
2
0
c
m
C
2
0
c
m
,
2
2
c
m
D
1
4
c
m
,
2
0
c
m
Medium
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Solution
Verified by Toppr
Correct option is B)
d
=
f
2
β
β
f
1
β
β
f
2
β
β
f
1
β
=
2
β
f
2
β
=
2
+
f
1
β
f
e
q
β
=
f
1
β
+
f
2
β
β
d
f
1
β
f
2
β
β
=
f
1
β
+
f
2
β
β
2
f
1
β
f
2
β
β
=
1
0
(
2
f
1
β
)
(
f
1
β
)
(
2
Γ
f
1
β
)
β
=
1
0
2
+
f
1
β
=
2
0
f
1
β
=
1
8
c
m
f
2
β
=
2
+
f
1
β
=
2
0
c
m
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