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Class 12
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Physics
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Ray Optics and Optical Instruments
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Combination of Lenses
Combination of Lenses
Revise with Concepts
Effective Focal Length of Lens
Example
Definitions
Formulaes
>
Newton's Formula for Thick Lenses
Example
Definitions
Formulaes
>
Combination of Lenses in Contact
Example
Definitions
Formulaes
>
Problems on Thin Lens
Example
Definitions
Formulaes
>
Problems on Lenses
Example
Definitions
Formulaes
>
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Learn with Videos
Power of a Lens
6 mins
Effective Focal Length
7 mins
Graphical Method of Determining Focal Length (Concave Mirror)
11 mins
Numericals on Combination of Lenses
10 mins
Complex Numericals based on Thin Lenses
7 mins
Quick Summary With Stories
Power of Lens
2 mins
Combination of Lenses in Contact
2 mins
Effective Focal Length
2 mins
Newton's Law for Thin Lenses.
3 mins
Solve Problems For Combination Of Lenses
2 mins
Complex Numericals Based on Thin Lenses
4 mins
Optics Problem-II
3 mins
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Important Questions
Two identical glass
$(μ_{g}=3/2)$
equiconvex lenses of focal length
$f$
are kept in contact. The space between the two lenses is filled with water
$(μ_{w}=4/3)$
. The focal length of the combination is
Medium
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Drive an expression for equivalent focal length of two thin lenses kept in contact.
Medium
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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 :
Medium
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A convex lens of focal length 20 cm is placed coaxially with a convex mirror of radius of curvature 20 cm. The two are kept at 15 cm apart from each other. A point object lies 60 cm in front of the convex lens. Draw a ray diagram to show the formation of the image by the combination. Determine the nature and position of the image formed.
Hard
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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 from the image of an object. At what distance from this lens an object be placed in order to have a real image of the size of the object :
Hard
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An object
$5cm$
is placed at a distance of
$20cm$
in front of a convex mirror of radius of curvature
$30cm$
. Find the position of the image, its nature and size.
Medium
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Diameter of plano-convex lens is 6 cm and thickness at the centre is 3 mm. If speed of light in material of lens is
$2×10_{8}m/s$
, the focal length of the lens is:
Hard
JEE Mains
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>
Two similar thin equi-convex lenses, of focal length f each, are kept coaxially in contact with each other such that the focal length of the combination is
$F_{1}$
. When the space between the two lenses is filled with glycerine (which has the same refractive index (
$μ=1.5$
) as that of glass) then the equivalent focal length is
$F_{2}$
. The ratio
$F_{1}:F_{2}$
will be :
Medium
NEET
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A plano-convex lens fits exactly into a plano-concave lens. Their plane surfaces are parallel to each other. If the lenses are made of different material of refractive indices
$μ_{1}$
and
$μ_{2}$
and R is the radius of curvature of the curved surface of the lenses, then focal length of the combination is :
Hard
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>
What is the focal length of a convex lens of focal length 30 cm in contact with a concave lens of focal length 20cm? Is the system a
converging or a diverging lens? Ignore thickness of the lenses.
Medium
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>