#### Question

For an object placed at distance 20 cm in front of a convex lens, the image is at distance 20 cm behind the lens. The focal length of convex lens is:

(a) 20 cm (b) 10 cm (c) 15 cm (d) 40 cm.

#### Solution

The focal length of the convex lens is 10 cm.

Hint: As the object distance = image distance, the object must be kept at 2f.

Therefore, 2f = 20 cm or f = 10 cm.

Is there an error in this question or solution?

Solution For an Object Placed at Distance 20 Cm in Front of a Convex Lens, the Image is at Distance 20 Cm Behind the Lens. the Focal Length of Convex Lens Is: (A) 20 Cm (B) 10 Cm (C) 15 Cm (D) 40 Cm. Concept: Concept Refraction of Light Through a Lense.