A convex lens of focal length 30 cm is placed in contact with a concave lens of focal length 20 cm. An object is placed at 20 cm to the left of this lens system. The distance of the image from the lens in cm is .

Question

Accepted Answer

(4) 15. Given: f₁=+30 cm, f₂=-20 cm, u=-20 cm. Lenses in contact: 1/F=1/(30)-1/(20)=-1/(60), so F=-60 cm. Lens formula: 1/v=1/F+1/u=-1/(60)-1/(20)=-4/(60). v=-15 cm: a virtual image 15 cm from the lens, on the object side.

A convex lens of focal length 30 cm is placed in contact with a concave lens of focal length 20 cm. An object is placed at 20 cm to the left of this lens system. The distance of the image from the lens in cm is ______.

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