W.B.C.S. Notes On – Physics – Spherical Lenses.
- A transparent material (normally glass) bound by two surfaces, of which one or both surfaces are spherical, is known as “spherical lens.”Continue Reading W.B.C.S. Notes On – Physics – Spherical Lenses.
- A lens may have two spherical surfaces, bulging outwards (as shown in the image given below), is known as convex lens or a double convex lens.
- The middle part of this lens is bulged (thicker) and at the both ends, it is narrow.
- Convex lens converges the light rays; therefore, it is also known as converging lens.
- A lens may have two spherical surfaces, curved inwards (as shown in the image given below), is known as concave lens or a double concave lens.
- The middle part of this lens is narrow (curved inwards) and the both the edges are thicker.
- Concave lens diverges the light rays; therefore, it is also known as diverging lens.
- A lens, either a concave or a convex, has two spherical surfaces and each of these surfaces forms a part of the sphere. The centers of these spheres are known as centers of curvature, represented by English letter ‘C.’
- As there are two centers of curvature, therefore, represented as ‘C1’ and ‘C2.’
- An imaginary straight line, passing through both the centers of curvature of a lens, is known as principal axis.
- Optical center is the central point of a lens. It is represented by ‘O.’
- An aperture is the actual diameter of the circular outline of a spherical lens.
- Principal focus of lens is represented by ‘F.’
- A lens has usually two foci represented as F1 and F2.
- Focal length is the distance between the principal focus and the optical center of a lens. It is represented by ‘f.’
- The following table illustrates, the nature and position of images formed by a convex lens −
|Position of Object||Position of Image||Size of Image||Nature of Image||Image|
|At infinity||At the focus F2||Highly diminished, pointsized||Real and inverted|
|Beyond 2F1||B/w F2 and 2F2||Diminished||Real and inverted|
|At 2F1||At 2F2||Same size||Real and inverted|
|B/w F1 & 2F1||Beyond 2F2||Enlarged||Real and inverted|
|At focus F1||At infinity||Infinitely large or highly enlarged||Real & inverte d|
|B/w focus F1& optical center O||On the same side of the lens as the object||Enlarged||Virtual and erect|
- The following table illustrates, the nature and position of images formed by a concave lens −
|Position of Object||Position of Image||Relative Size of Image||Nature of Image||Image|
|At infinity||At the focus F1||Highly diminishe d, pointsized||Virtual and erect|
|B/w infinity & optical center O of the lens||B/w F1 & optical center O||Diminishe d||Virtual and erect|
- The formula is expressed as −
- Lens formula expresses the relationships among the object-distance (i.e. u), image-distance (i.e. v), and focal length (i.e. f) of a lens.
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