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JEE Main Physics Class 12 Ray Optics and Optical Instruments Part 1 Questions
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Question : 14
Total: 99
A point object in air is in front of the curved surface of a plano-convex lens. The radius of curvature of the curved surface is 30 cm and the refractive index of the lens material is 1.5, then the focal length of the lens (in cm) is__________.
[NA 8 Jan. 2020 I]
Your Answer:
Validate
Solution:
Given
:
µ
=
1.5
;
R
curved
=
30
c
m
Using, Lens-maker formula
1
f
=
(
µ
−
1
)
(
1
R
1
−
1
R
2
)
For plano-convex lens
R
1
→
∞
then
R
2
=
−
R
∴
f
=
R
µ
−
1
=
30
1.5
−
1
=
60
c
m
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