# A convex lens have focal length 30cm at what distance the object must be placed to form an image at 60cm?

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A convex lens have focal length 30cm at what distance the object must be placed to form an image at 60cm?
posted Oct 2, 2018

Lens formula,
1/v - 1/u = 1/f
where,
v = image distance from lens
u = object distance from lens
f = focal length

here ,
f = 30 cm { for convex lens f is positive }
v = 60cm

1/60 - 1/u = 1/30 -> 1/60 - 1/30 = 1/u -> -1/60 = 1/u -> u = -60 cm
hence, object distance also 60cm but left side of convex lens . in which position of image is right side.

magnification = ( image distance )/(object distance ) = 60/(-60) = -1
it means height of image = height of object . but both lies just opposite sides of lens .

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