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TS EAMCET 4-Aug-2021 Shift 2 Question Paper
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© examsnet.com
Question : 104
Total: 160
Two lenses of power
−
1.6
D
and
+
2.1
D
respectively are placed in contact. The focal length of the combination is
100 cm
200 cm
160 cm
210 cm
Validate
Solution:
Given, power of lenses
P
1
=
−
1.6
D
and
P
2
=
+
2.1
D
Let, the respective focal lengths be
f
1
,
f
2
and their equivalent focal length be
f
.
∵
1
f
=
1
f
1
+
1
f
2
. . . (i)
Power
=
1
f
(
m
)
∴
From Eq. (i), we get
P
net
=
P
1
+
P
2
⇒
P
net
=
−
1.6
D
+
2.1
D
=
0.5
D
⇒
1
f
=
1
2
∴
f
=
2
m
=
200
c
m
© examsnet.com
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