When using the lens equation, a real object has a positive object distance – choice B.
The lens equation is a vital topic in the study of optics and physics in general. It helps in the quantification of the relationship between an image and an object. There are three main concepts involved in the lens equation and that includes image distance, focal length and object distance. The object distance is defined as the space between the point of incidence where the light rays fall on a lens and the object itself.
The image distance is the space between the image and the lens. The focal length is the distance from the lens’ center to its focal point. Image distance can either be negative or positive for a virtual or real image respectively.