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AIEEE 2004 Physics Solved Paper
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© examsnet.com
Question : 63
Total: 78
A plano convex lens of refractive index
1.5
and radius of curvature
30
cm
. Is silvered at the curved surface. Now this lens has been used to form the image of an object. At what distance from this lens an object be placed in order to have a real image of size of the object
60 cm
30 cm
20 cm
80 cm
Validate
Solution:
KEY CONCEPT : The focal length
(
F
)
of the final mirror
is
1
F
=
2
f
ℓ
+
1
f
m
Here
1
f
ℓ
=
(
µ
−
1
)
(
1
R
1
−
1
R
2
)
=
(
1.5
−
1
)
[
1
α
−
1
−
30
]
=
1
60
∴
1
F
=
2
×
1
60
+
1
30
∕
2
=
1
10
∴
F
=
10
cm
The combination acts as a converging mirror. For the object to be of the same size of mirror,
u
=
2
F
=
20
cm
© examsnet.com
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