Q. 114.3( 96 Votes )

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

Answer :

Here, Object distance, u = ? (To be calculated)

Image distance, v =- 10 cm (To the left of concave lens)

Focal length, f =- 15 cm (It is a concave lens)

Now, putting these values in the lens formula:

Putting the values  of v and f in the above equation, we get

Object distance, u = -30 cm

Thus, the object is placed at a distance of 30 cm from the concave lens. The minus sign with object distance shows that the object is on its left side. The diagram is shown as:

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