Question

Concave lens has a focal length 15cm. What should be the distance of the object from the lens to form image at 10cm from lens? Marking best answer as brainliest

Answer 1

f= -15

v= -10

u= ?

lens formula 1/f= 1/v - 1/u

1/u = 1/v - 1/f

1/u = 1/ -10 - 1/-15

1/u =  -1/10 + 1/15

1/u = -3+2/30  (taking LCM)

1/u = -1/30

u = -30

thus, object should be placed at a distance of 30 cm...

magnification = v/u

m = -10/-30

m = 1/3

m= 0.33

Answer 2

v = -10 cm

f = -15 cm

1/v - 1/u = 1/f
-1/10 - 1/u = -1/15
-1/10 + 1/15 = 1/u
-3+2/30 = 1/u
-1/30 = 1/u

u = -30cm

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