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Important Questions on Refraction at Spherical Surface and Spherical Lens

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Physics>Optics>Refraction at Spherical Surface and Spherical Lens>Some Basic Definitions in Lens
A convex lens has 20cm focal length in air. What is the focal length in water? [Refractive index of water =1.33, Refractive index of air-glass =1.5]
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Physics>Optics>Refraction at Spherical Surface and Spherical Lens>Some Basic Definitions in Lens
A small telescope has an objective lens of focal length 140cm and eyepiece of focal length 50cm. What is the magnifying power of telescope when image is at infinity and image is formed at least distance of distinct vision?
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Physics>Optics>Refraction at Spherical Surface and Spherical Lens>Some Basic Definitions in Lens

A screen is placed at a distance of 90 cm from an object. A convex lens forms the image of this object on the screen, when placed at two different locations separated by 30 cm as shown in the figure. Determine the focal length of the lens.

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Physics>Optics>Refraction at Spherical Surface and Spherical Lens>Some Basic Definitions in Lens
The size of the image of an object, which is at infinity, as formed by a convex lens of focal length 30 cm is 2 cm. If a concave lens of focal length 20 cm is placed between the convex lens and the image at a distance of $26 \mathrm{~cm}$ from the lens, the new size of the image is:
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Physics>Optics>Refraction at Spherical Surface and Spherical Lens>Some Basic Definitions in Lens
What focal length should the reading spectacles have for a person for whom the least distance of vision is 50 cm? (The normal distance of vision is 25 cm).
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Physics>Optics>Refraction at Spherical Surface and Spherical Lens>Some Basic Definitions in Lens
Deduce the relation between object and image distance in terms of refractive index of the medium and the radius of curvature of curved spherical surface.
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Physics>Optics>Refraction at Spherical Surface and Spherical Lens>Some Basic Definitions in Lens

A person who can see the object clearly at a distance of 10 cm, requires spectacles to be able to see clearly objects at a distance of 30 cm. What type of spectacles should he use? Find the focal length of the lens.

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Physics>Optics>Refraction at Spherical Surface and Spherical Lens>Some Basic Definitions in Lens
Focal length of a convex lens in air is 25 cm. If it is immersed in water, then calculate the focal length of the lens. nw=43, ng=32
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Physics>Optics>Refraction at Spherical Surface and Spherical Lens>Some Basic Definitions in Lens

Assertion (A): The focal length of lens does not change when red light is replaced by blue light.

Reason (R): The focal length of lens does not depend in colour of light used.

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Physics>Optics>Refraction at Spherical Surface and Spherical Lens>Some Basic Definitions in Lens
Sunlight of intensity 1.3 kW m-2 is incident normally on a thin convex lens of focal length 20 cm. Ignore the energy loss of light due to the lens and assume that the lens aperture size is much smaller than its focal length. The average intensity of light, in kW m-2 , at a distance 22 cm from the lens on the other side is __________.
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Physics>Optics>Refraction at Spherical Surface and Spherical Lens>Some Basic Definitions in Lens
A convex lens forms an image of an object placed 20 cm away from it at a distance of 20 cm on the other side of the lens. If the object is moved 5 cm towards the lens, the image will move
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Physics>Optics>Refraction at Spherical Surface and Spherical Lens>Some Basic Definitions in Lens
The distance v of the real image formed by a convex lens is measured for various object distance u. A graph is plotted between v and u. Amongst the following which graph is correct 
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Physics>Optics>Refraction at Spherical Surface and Spherical Lens>Some Basic Definitions in Lens
A thin convex lens forms a real image of a certain object 'p' times its size. The size of real image becomes 'q' times that of object when the lens is moved nearer to the object by a distance 'a' find focal length of the lens?
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Physics>Optics>Refraction at Spherical Surface and Spherical Lens>Some Basic Definitions in Lens
Spherical aberration in a lens
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Physics>Optics>Refraction at Spherical Surface and Spherical Lens>Some Basic Definitions in Lens
Graph of position of image versus position of point object from a convex lens is shown. Then, focal length of the lens is

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Physics>Optics>Refraction at Spherical Surface and Spherical Lens>Some Basic Definitions in Lens
Two thin lenses of power +6D and –2D are in contact. The focal length of the combination would be:
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Physics>Optics>Refraction at Spherical Surface and Spherical Lens>Some Basic Definitions in Lens

Look at the ray diagram shown, what will be the focal length of the 1st and the 2nd lens, if incident light ray is parallel to emergent ray.


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Physics>Optics>Refraction at Spherical Surface and Spherical Lens>Some Basic Definitions in Lens
A real image is formed by a convex lens. If we put a concave lens in contact with it, the combination again forms a real image. The new image
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Physics>Optics>Refraction at Spherical Surface and Spherical Lens>Some Basic Definitions in Lens
Consider a system of thin lenses and mirror, as shown in the diagram. Refractive indices of the media are given as μ1, μ2 and μ 3  and the radii of curvature of interfaces are given as R1, R2 and R3, then, the magnitude of focal length of the system is(take μ1=μ, μ2=2μ, μ3=3μ  and R1=R, R2=R3=2R)
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Physics>Optics>Refraction at Spherical Surface and Spherical Lens>Some Basic Definitions in Lens
What cause chromatic aberration?