Where should an object be placed in front of a convex lens to get a real image of the size of the object?

At the principal focus of the lens.

Between the optical centre of the lens and its principal focus.

Draw a ray diagram and describe the image formation by a concave lens when an object is placed at (i) infinity (ii) a finite distance.

Image formation by a concave lens: When an Object is placed at Infinity: (i) When an object is placed at infinity, a virtual image is formed at the principal focus. (ii)The size of the image is much smaller than that of the object. When the object is placed anywhere on the principal axis at a finite distance: (i) First, we draw a ray parallel to the principal axis so, it appears to pass through focus after reflection. We draw another ray that passes through the optical centre so, the ray will go through without any deviation. Where both reflected rays meet is the point A ' . (ii) The image is formed between F 1 an Optical centre, The image is behind the mirror which is a real image, erect and smaller than the object which is diminished.

Draw a ray diagram and describe the image formation by a convex mirror when an object is placed at (i) infinity (ii) a finite distance.

(a) at infinity When an object is placed at infinity, the image formed is virtual, erect, and highly diminished. So the image formed is a point size image. (b) at a finite distance from the mirror. When the object is placed at a finite distance from the mirror the image is formed between the pole and principal focus.