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Category: Ray optics and optical instruments

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PRINCIPAL OF REVERSIBILITY OF LIGHT RAYS

“A ray travelling along the path of the reflected ray is reflected along the path of the incident ray.” In the same way, a refracted ray reversed to travel back along its path will get refracted along the path of the incident ray. Thus the incident and refracted rays are mutually reversible. Now according to […]

MIRROR FORMULA

The formula which gives relationship between distances of object (u), image distance (v) and the focal length (f) of the mirror is called as mirror formula. Assumptions: (a) Only small aperture mirror must be considered i. e for paraxial rays. (b) The rays of light should not be incident vary obliquely. We assume that P […]

SIGN CONVENTION

We follow the ‘new Cartesian sign convention’. The pole of the mirror is taken to be at origin of the rectangular coordinate system. Accordingly, we shall use the following convention regarding the sign of various quantities. (a) All distances are measured from pole of mirror. (b) The distances measured in the same direction as the […]

RELATION BETWEEN ‘RADIUS’ AND ‘FOCAL LENGTH’ OF A SPHERICAL MIRROR

Let us consider a parallel beam of light falls on concave and convex mirrors. The law of reflection are applied at each point. The normal to the surface at the point ‘M’ is ‘CM’. After reflection, the ray converges to the point ‘F’ (as in the case of convex mirror). Let incident ray makes an […]

GRAPHICAL METHOD FOR FORMATION OF IMAGE BY SPHERICAL MIRRORS

(a) Concave mirror: Case 1: when object is at infinity. Case 2: when object is beyond ‘c’. Case 3: when object is at ‘c’. Case 4: When object is between ‘c’ and ‘F’. Case 5: When object is at ‘F’. Case 6: When object is between pole and focus. (b) Convex mirror: Case 1: When […]

FORMATION OF IMAGES BY SPHERICAL MIRRORS

The best method for formation of images by mirror is through ray tracing. The point at which reflected rays will intersect gives the location of images. (a) A ray parallel to the axis, after reflection, passes through the focal point of a concave mirror or appears to come from the focal point of a convex […]

SPHERICAL MIRRORS:

SPHERICAL MIRRORS: Spherical mirror are part of spherical reflecting surfaces. It has two types: (1) Concave mirror: When the reflection takes place from inner surface (polished or silvered on outer surface) called concave mirror or converging mirror. (2) Convex mirror: When the reflection takes place from outer surfaces (polished or silvered on inner surface) called […]

TELESCOPE

It is used to provide angular magnification of the distant objects. It is of two types: (1) Retracting type telescope (2) Reflecting type telescope RETRACTING TYPE TELESCOPE: It is of two types. (a) Astronomical telescope (b) Terrestrial telescope A telescope used to see heavenly bodies is called astronomical telescope. It produces a virtual and inverted […]

DISPERSION

The phenomenon of splitting of light into its component colours is known as dispersion. SPECTRUM: The pattern of colour components of light is called the spectrum. ANGULAR DISPERSION: “The angle between the two rays corresponding to the extreme colours red and violet in the spectrum is called angular dispersion”. DISPERSIVE POWER: The ratio of angular […]

SCATTERING OF LIGHT IN ATMOSPHERE

When sunlight travels through the earth’s atmosphere, it get scattered by the large number of molecules present. This scattering of sunlight is responsible for the colour of the sky, colour during sunrise and sunset etc. According to Ray leigh’s criterian, the amount of scattering is inversely proportional to the fourth power of wavelength known as […]

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