Question

concave lens has focal length of 15 cm at what distance should start from the lens be placed so that it forms an image at 10 cm from the lens also find the magnification produced by the lens? ​

Answer 1

Answer:

object distance, u=?, image distance, v=-10cm, magnification of lens, m=? Thus the object should be placed at a distance of 30 cm on the left side of the concave lens. Linear magnification, m=vu=-10-30=13.

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Answer 2

Explanation:

A concave lens always forms a virtual, erect image on the same side of object .

image distance (v) =-10 cm

Focal length (f) =-15 cm

object distance (u) =?

since 1/v-1/u=1/f

or,

1/u=1/v-1/f

1/u=1/-10-1/(-15)=-1/10+1/15

1/u=-3+2/30=1/-30

u=-30 cm

Thus, the object distance is 30 cm

Magnification m=v/u

m=-10 cm/-30 cm=1/3=+0.33

The positive sign shows that the image is erect and ritual the image is on third of the size of the object ..