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An object is placed at a distance of 5 cm more than the focal length f of a convex lens. Its real image is formed at a distance 3f beyond the focus. The focal length f of the lens is:

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Important Questions on Refraction of Light at Spherical Surfaces : Lenses

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12th ICSE
IMPORTANT
ISC Physics Class 12, Part-2>Chapter 3 - Refraction of Light at Spherical Surfaces : Lenses>QUESTIONS>Q 6
The focal length of a convex lens of glass of refractive index 1.50 is 2 cm. The focal length of the lens when immersed in a liquid of refractive index 1.25 will be:
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12th ICSE
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ISC Physics Class 12, Part-2>Chapter 3 - Refraction of Light at Spherical Surfaces : Lenses>QUESTIONS>Q 7
A double convex lens of glass (n=1.5) has a focal length of 10 cm in air. When immersed in a liquid of refractive index 3.0, the lens will behave as:
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ISC Physics Class 12, Part-2>Chapter 3 - Refraction of Light at Spherical Surfaces : Lenses>QUESTIONS>Q 8
A symmetric double convex lens of power 4 D is cut in two halves by a plane perpendicular to the principal axis. The power of each half is:
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12th ICSE
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ISC Physics Class 12, Part-2>Chapter 3 - Refraction of Light at Spherical Surfaces : Lenses>QUESTIONS>Q 9
A symmetric double convex lens of power 4 D is cut in two halves by a plane containing the principal axis. The power of each half is:
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12th ICSE
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ISC Physics Class 12, Part-2>Chapter 3 - Refraction of Light at Spherical Surfaces : Lenses>QUESTIONS>Q 10

Two identical plano-convex lenses can be combined in three ways, as shown. The ratio of the focal lengths of these combinations will be:

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12th ICSE
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ISC Physics Class 12, Part-2>Chapter 3 - Refraction of Light at Spherical Surfaces : Lenses>QUESTIONS>Q 11
A convex lens of power +6 dioptre is placed in contact with a concave lens of power -4 dioptre. What will be the nature and focal length of this combination?
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12th ICSE
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ISC Physics Class 12, Part-2>Chapter 3 - Refraction of Light at Spherical Surfaces : Lenses>QUESTIONS>Q 12
Two thin lenses having optical powers of -10 D and +6 D are placed in contact with each other. The focal length of the combination is:
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12th ICSE
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ISC Physics Class 12, Part-2>Chapter 3 - Refraction of Light at Spherical Surfaces : Lenses>QUESTIONS>Q 13
A lens of power +2 D is placed in contact with a lens of power -1 D. The combination will behave like: