Why can’t some images be obtained on a screen i.e. what are real and virtual object (image)?
Objects and images may be real or virtual. If light rays, after reflection or refraction, pass through the point where the image is located then the image is called a real image. But if the light rays appear to come from a point where the image is located then the image is called a virtual image. Similar is the case with objects. The object is said to be real if light rays actually diverge from the point where the object is. If the light rays only appear to go towards the point where the object is located then the object is said to be virtual.