Question

Q-4 optical system formed by the
convex lenses has focal length of 15
cm and 12 cm then its effective
focal length will be
O 6.66 cm
O 7.2 cm
O
5.0 cm
O 17cm​

Answer 1

a convex lens of focal length 10 cm is placed at a distance of 12 cm from a wall. How far from the lens should an object be placed so as to form its real image on the wall?

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Updated On: 21-9-2020

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Solution

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. <br> Now, Image distance,

cm (A real image) <br> Object distance, u=? (To be calculated) <br> Focal length, f=+10 cm (it is convex lens) <br> Putting these values in the lens formula: <br>

<br> We get:

<br>

<br>

<br>

<br> So, Object distance, u=-60 cm <br> 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.