3. Explain formation of an image by plane mirror in case of
point object and object with certain height?
Answers
You only have to look as far as the nearest bathroom to find an example of an image formed by a mirror. Images in a plane mirror are the same size as the object, are located behind the mirror, and are oriented in the same direction as the object (i.e., “upright”).
To understand how this happens, consider (Figure). Two rays emerge from point P, strike the mirror, and reflect into the observer’s eye. Note that we use the law of reflection to construct the reflected rays. If the reflected rays are extended backward behind the mirror (see dashed lines in (Figure)), they seem to originate from point Q. This is where the image of point P is located. If we repeat this process for point {P}^{\prime }, we obtain its image at point {Q}^{\prime }. You should convince yourself by using basic geometry that the image height (the distance from Q to {Q}^{\prime }) is the same as the object height (the distance from P to {P}^{\prime }). By forming images of all points of the object, we obtain an upright image of the object behind the mirror.
Two light rays originating from point P on an object are reflected by a flat mirror into the eye of an observer. The reflected rays are obtained by using the law of reflection. Extending these reflected rays backward, they seem to come from point Q behind the mirror, which is where the virtual image is located. Repeating this process for point {P}^{\prime } gives the image point {Q}^{\prime }. The image height is thus the same as the object height, the image is upright, and the object distance {d}_{\text{o}} is the same as the image distance {d}_{\text{i}}. (credit: modification of work by Kevin Dufendach)