CBSE 2026 · Region 3 · Set 1 · Q38

The variation of image distance $\displaystyle (v)$ with the object distance $\displaystyle (u)$ for a convex lens is given in the following observation table. Analyse it and answer the questions given below :

S.No.	Object distance $\displaystyle (u) \mathrm{cm}$	Image distance (v) cm
$\displaystyle 1$	- $\displaystyle 150$	+ $\displaystyle 30$
$\displaystyle 2$	-$\displaystyle 75$	+ $\displaystyle 37$•$\displaystyle 5$
$\displaystyle 3$	-$\displaystyle 50$	+$\displaystyle 50$
$\displaystyle 4$	- $\displaystyle 37$•$\displaystyle 5$	+$\displaystyle 75$
$\displaystyle 5$	-$\displaystyle 30$	+ $\displaystyle 150$
$\displaystyle 6$	-$\displaystyle 15$	+$\displaystyle 37$•$\displaystyle 5$

(a)

Without calculation, find out the focal length of the given convex lens. Justify your answer.

(b)

Which one of the observations given in the table is not correct and why ?

(c)

(i)OR(c)

Find out the value of magnification for $\displaystyle u=-30 \mathrm{~cm}$. Write the nature of the image formed. Give reason for your answer.

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