CBSE Class 12 Physics Notes: Ray Optics – Important Definitions

We define a varied collection of useful terms. Some of these definitions will be revisited when the appropriate topics are taken up.

(i) Ray: The path of light, as determined within the approximations of geometric optics, is a ray. In a homogeneous medium, it is a straight line.

(ii) Beam: A collection of rays, usually referred to as a bundle of rays, forms a beam. One may have a convergent, divergent or, a parallel beam. A convergent beam may converge to a point or, a line, a divergent beam may diverge from a point or, a line. A parallel beam consists of parallel rays.

(iii) Collimation: A process whereby a divergent (or, convergent) beam is rendered parallel usually through the use of lenses and/or mirrors.

(iv) Object & Image: The term object is used to refer to any object (being photographed or observed) that is a source of light, and its likeness (usually two dimensional) formed or observed by an optical system is the image.

(v) Optical System: An optical system consists of elements like lenses, mirrors, prisms, etc.

(vi) Axis: The axis of an optical system is frequently an axis of symmetry such that a ray directed along the axis continues in the same direction or, returns backwards (if reflected within the system)

(vii) Centre of Curvature: Most lenses and curved mirrors being manufactured spherical (i.e., their surfaces are spherical), the centre of curvature of the curved mirror or, the curved surface of a lens is important and is frequently denoted by the letter C. The radius of curvature is also equally important in the analysis.

(viii) Pole: The pole of a spherical surface (refracting or, reflecting) is the central point of the surface involved in the formation of the image. It is denoted by O or, P. The axis, for a single spherical surface, is the join of the pole with the centre of curvature; it is known as the principal axis.

(ix) Optical Centre: The optical centre of a thin lens is a point on the axis of the lens such at a ray directed towards that point emerges parallel to itself after passing through the lens.

(x) Paraxial Rays: It is observed that the formation of clear images by spherical surfaces takes place only with rays which are close to the principal axis and make very small angles with it.

CBSE Class 12 Physics Notes: Ray Optics   Important Definitions
CBSE Class 12 Physics Notes: Ray Optics   Important Definitions

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