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Combination of Lenses
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A convex lens of focal length 40 cm is i
Question
A convex lens of focal length 40 cm is in contact with a concave lens of focal length 25 cm. The power of he combination, is :
A
+
6
.
6
7
D
B
β
6
.
5
D
C
β
1
.
5
D
D
+
6
.
5
D
Medium
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Solution
Verified by Toppr
Correct option is C)
Given,
f
1
β
=
+
4
0
c
m
f
2
β
=
β
2
5
c
m
Power,
P
=
f
1
β
The power of combination,
P
=
f
1
β
1
β
+
f
2
β
1
β
P
=
+
4
0
c
m
1
0
0
β
+
β
2
5
c
m
1
0
0
β
P
=
β
1
.
5
D
The correct option is C.
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Assertion
If a convex lens of focal length 40 cm is put in contact with a concave lens of 25 cm, then the power of the combination is -
1
.
5
D
.
Reason
P
=
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β
+
P
2
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=
f
1
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+
f
2
β
1
β
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