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When an object is placed normallyon the principal axis of a spherial mirror at a distance 'a' from its pole, its image is formed at a distance 'v' from the pole of mirror such that (1)/(v)+(1)/(u)=(1)/(f), where f = focal length of given mirror. The relation is called mirror formula and is true for all types of mirrors under all conditions. However, values of u, v and f must be put with proper signs are per the sign convention followed. If 'h' be the height of the linear object and h' the height of image, then ratio (h')/(h) is called linear magnification or lateral magnification and its value m is given as : m=(h')/(h)=-(v)/(u) (a) A planer object of length 3 cm and breadth 2 cm is held normal to the principal axis of a concave mirror of focal length 20 cm at a distance of 30 cm from its pole. Where is its image formed? |
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Answer» Solution :(a) Here `u=-30cm, f=-20cm` and area of PLANAR object `A=lb=3xx2=6cm^(2)`. `THEREFORE""(1)/(v)=(1)/(f)-(1)/(u)=(1)/((-20))-(1)/((-30))=-(1)/(60)` `RARR""v=-60cm` thus, image is formed in front of mirror at a distance of 60 cm from the POLE. |
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