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Define: a) Diffraction b) Relation between focal length and radius of curvature and also proof it? c) between which two points related to a concave mirror ,should an object be placed to obtain on a screen an image twice the size of the object d) lateral displacements and its calculation.
Asked by spankaj.ekt | 30 Apr, 2020, 07:53: AM
a) Diffraction is the phenomenon of bending of light around the corners of small apertures or obstacles and its spreading into the region of the geometrical shadow.

b)

### The relationship between the focal length f and radius of curvature r is r = 2f.Consider a ray of light AB, parallel to the principal axis and incident on a spherical mirror at point B. The normal to the surface at point B is CB and CP = CB = R, is the radius of curvature. The ray AB, after reflection from mirror, will pass through F (concave mirror) or will appear to diverge from F (convex mirror) and obeys the law of reflection i.e. i = r.From the geometry of the figure,∠BCP = θ = iIn D CBF, θ = r∴BF = FC (because i = r)If the aperture of the mirror is small, B lies close to P, and therefore BF = PFOr FC = FP = PFOr PC = PF + FC = PF + PFOr R = 2 PF = 2fOr f = R/2Similar relation holds for convex mirror also. In deriving this relation, we have assumed that the aperture of the mirror is small.

c) object must be placed between C and F

d)

### A ray of light travels in a certain straight line path. After refraction through a glass slab, it emerges in a direction parallel to the original direction but slightly displaced from the line. This is called the lateral displacement.

Answered by Shiwani Sawant | 30 Apr, 2020, 01:01: PM

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