Q. 235.0( 2 Votes )

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Answer :

(a)


The image formed is – behind the object (on the left side of lens)


- Virtual and erect


- Larger than the object


(b) According to the new Cartesian sign convention the following are the rules-


(i) All the distances are measured from the optical centre of lens


(ii) The distances measured in same direction as that of incident light are taken positive.


(iii) The distances measured against the direction of the incident light are taken negative.


(iv) The distances measured upwards and perpendicular to the principal axis are taken positive, others negative.



The focal length of convex lens is considered positive, for concave lens it is negative.


The relation between u, v and f is given by the lens formula


As both (u) and (v) are negative, the above equation will change to:





(c) given u= -20cmm = -1


magnification m= v/u


v=mu


= -1 × -20 = 20cm


Thus, v = 20 cm


Now, focal length is given as:




f = 10cm


Now, we know,



P = 10 D


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