Question

at what distance should an object be placed from a convex lens of focal length 18 cm to obtain an image at 36 cm from it what will be the magnification produced in this case​

Answer 1

Answer:

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$\mathrm{f}=18 \mathrm{cm}$

Focal length

$v=24 \mathrm{cm}$

Distance of image

Using lens formula to find the position of object u.

According to lens formula,

$\frac{1}{f}=\frac{1}{v}-\frac{1}{u}$

Substituting the values  

$\frac{1}{18}=\frac{1}{36}-\frac{1}{u}$

u = -36 cm

Therefore the object must be placed at a distance of 36 cm from the focal length of the lens.

And the magnification of the image formed will be inverted this could be seen by the negative sign obtained. And this sign indicates the position in respect to the coordinate where the focal length of the lens is placed.

Answer 2

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$\mathfrak{f}=18 \mathrm{cm}$

Focal length

$\sf v=24 \mathrm{cm}$

Distance of image

Using lens formula to find the position of object u.

According to lens formula,

$\sf\frac{1}{f}=\frac{1}{v}-\frac{1}{u}$

Substituting the values

$\sf\frac{1}{18}=\frac{1}{36}-\frac{1}{u}$

u = -36 cm

Therefore the object must be placed at a distance of 36 cm from the focal length of the lens.

And the magnification of the image formed will be inverted this could be seen by the negative sign obtained. And this sign indicates the position in respect to the coordinate where the focal length of the lens is placed.

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