A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens ? Draw the ray diagram.

Explanation

`{:("Concave lens","Object","Image"),(f=-15 cm,u=?,v=-10 cm),(r=2f=-30 cm,,"Nature of image = ?"):}`
The focal length of the concave lens is 15 cm. The image is formed at a distance of 10 cm from the concave lens. The image is formed between optic centre (O) and `F_(1)`.
Lens formula
`(l)/((-10))-(l)/(u)=(l)/((-15)),(l)/(u)=-(1)/(10)+(1)/(15), (l)/(u)=-(5)/(150)`,
`u=-30 cm`
The object is at a distance of 30cm on the left side of the concave lens. (-ve sign signifies this).