How does the lens form an image ?

Does eye lens form a real image or virtual image ?

How much time does the impression of an image stays in the retina?

How does the image formed on retina help us to precieve the object without change its shape , size and colour ?

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 ?

A convex lens has a focal length of 25 cm. Calculate the distance of the object from the lens if the image is to be formed on the opposite side of the lens at a distance of 75 cm from the lens. What will be nature of image ?