Question

17. At what distance should an object be placed from a convex lens of focal length 18 cm to obtain an image af
24 cm from it on the other side ? What will be the magnification produced in this case ?​

Answer 1

Answer:

72 cm and the magnification is -0.333.

so u= -72cm

Answer 2

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By using lens formula, 

1 / v − 1 / u = f1

where v = 24cm , f = 18cm

1 /24 − 1 /u = 181

from this we get  u = −72cm

magnification of lens is m = v / u

m = 24 / −72 = −31