The magnification produced by a plane mirror is +1. What does this mean?
The magnification produced by a plane mirror is +1. This means that the image formed is erect and virtual. The positive sign of magnification indicates that the image is erect (not inverted). The value of magnification being 1 means that the height of the image is equal to the height of the object (h' = h). In other words, the image formed by a plane mirror is of the same size as the object. Since magnification m = h'/h = +1, the image is neither enlarged nor diminished.
Explanation
According to the textbook context, magnification is defined as the ratio of the height of the image to the height of the object (m = h'/h). The context also states that the negative sign of magnification indicates an inverted and real image. Therefore, a positive magnification (+1) indicates an erect image. Since the magnitude is 1, the image height equals the object height, meaning the image is the same size as the object. For a plane mirror, this makes sense as it always forms a virtual, erect image of the same size as the object.