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The variation of image distance ($v$) with the object distance ($u$) for a convex lens is given in the following observation table. Analyse it and answer the questions given below :
(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?
| S.No. | Object distance ($u$) cm | Image distance ($v$) cm |
|---|---|---|
| --- | --- | --- |
| 1 | $-150$ | $+30$ |
| 2 | $-75$ | $+37.5$ |
| 3 | $-50$ | $+50$ |
| 4 | $-37.5$ | $+75$ |
| 5 | $-30$ | $+150$ |
| 6 | $-15$ | $+37.5$ |
(b) Which one of the observations given in the table is not correct and why?
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(c) $m = \frac{v}{u} = \frac{150}{-30} = -5$
Nature of image: Image will be real and inverted
Reason: because the value of m is negative.
Nature of image: Image will be real and inverted
Reason: because the value of m is negative.