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A Convex lens of focal lenth 10 cm is placed at a distance of 12 cm from a wall,Calculate the distance from the lens where an object be placed so as to form its distinct real images on the wall. plz solve .............

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Here, the real image is formed on the wall which is at a distance of 12 cm from the convex lens. This means that the distance of image from the convex lens or image distance will be 12 cm. Since a real image is fomred on the right side of the lens, so this image distance will be positive.
Now, Image distance, v=±12v (A real image)
Object distance, u=? (To be calculated)
Focal length, f=+10 cm (it is convex lens)
Putting these values in the lens formula:
\\ \frac{1}{v}-\frac{1}{u}=\frac{1}{f}$ \\ \\ We get: $\frac{1}{12}-\frac{1}{u}=\frac{1}{10}$ \\ \\ $\frac{1}{12}-\frac{1}{10}=\frac{1}{u}$ \\ \\ $\frac{5-6}{60}=\frac{1}{u}$ \\ \\ $-\frac{1}{60}=\frac{1}{u}$ \\ \\ So, Object distance, u=-60 cm

Thus, the obect should be place at a distance of 60 cm in front of the convex lens. The minus sign shows that the obect is on the left side of the lens.

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Deependra Verma

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