An object is placed at the focus of a concave lens. Where will be image ?

An object is placed at the focus of concave lens. Where will its image be formed?

An object is placed at the focus of Convex lens. Where will the image be formed?

If an object is placed at the focus of a convex lens, where is the image formed?

If an object is placed at the focus of a concave mirror, where is the. image formed?

If an object is placed at the focus of a concave mirror, where is the image formed?

An extended object is placed at the principal focus of a lens. Where will the final image be formed? Comment on the nature of the image.