A convex lens forms an image at 30 cm from lens on a screen.if the focal length of lens is 20 cm, find the distance at which the object is placed.
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A convex lens forms an image at 30 cm from lens on a screen.if the focal length of lens is 20 cm, find the distance at which the object is placed.
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Image distance, v=30cm
Focal length, f=20cm
Object distance, u=?
Using lens formula-
1/f=1/v-1/u
1/20=1/30-1/u
-1/u=1/20-1/30
-1/u=30-20/600
-1/u=10/600
-1/u=1/60
u=-60
so the object distance u=60cm.
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