- Introduction
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- Refraction through a rectangular glass slab
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- Laws of refraction of light
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- The Refractive Index
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- Refraction by Spherical Lenses
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- Image Formation by Lenses
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- Image Formation in Lenses Using Ray Diagrams
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- Sign Convention for Spherical Lenses
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- Lens Formula and Magnification

- All the distances are measured from the optical center of the lens.
- The distances measured in the same direction as that of incident light are taken as positive.
- The distances measured against the direction of incident light are taken as negative.
- The distances measured upward and perpendicular to the principle axis are taken as positive.
- The distances measured downwards and perpendicular to principle axis is taken as negative.

- Lens Formula gives the relationship between object distance (u), image image-distance (v) and the focal length (f ) and is expressed as

\( \frac{1}{f} = \frac{1}{v} - \frac{1}{u} \)

This formula is valid in all situations for any spherical lens. - The magnification produced by a lens is defined as the ratio of the height of the image and the height of the object.

- Magnification produced by a lens is also related to the object-distance u, and the image-distance v and is given by

\( m = \frac{v}{u} \) - The power of a lens is defined as the reciprocal of its focal length. It is represented by the letter P. The power P of a lens of focal length f is given by

\(P = \frac{1}{f}\) - Power of a convex lens is positive and that of a concave lens is negative.
- The SI unit of power of a lens is ‘dioptre’. It is denoted by the letter D.
- 1 dioptre is the power of a lens whose focal length is 1 meter so, 1D=1m–1.

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