Images formed by Spherical Mirrors

Images formed by Spherical Mirrors

Images formed by spherical mirrors are of two types: real image and virtual image. Real images can be formed on a screen, while virtual images cannot be formed on a screen. Image formed by a convex mirror is alway serect, virtual and diminished in size. As a result, images formed by these mirrors cannot be projected on a screen.

The characteristics of an image are determined by the location of the object. As the object gets closer to a concave mirror, the image gets larger, until attaining approximately the size of the object, when it reaches the centre of curvature of the mirror. As the object moves away, the image diminishes in size and gets gradually closer to the focus, until it is reduced to a point at the focus when the object is at an infinite distance from the mirror. The size and nature of the image formed by a convex mirror are given in Table 3. 1.

Concave mirrors form a real image and it can be caught on a screen. Unlike convex mirrors, concave mirrors show different image types. Depending on the position of the object in front of the mirror, the position, size and nature of the image will vary. Table 3. 2 provides a summary of images formed by a concave mirror.

You can observe from the table that aconcave mirror always forms a real and invertedimage except when the object is placed between the focus and the pole of the mirror. In thisposition, it forms a virtual and erect image.

Activity 1

Take a curved silver spoon and see the image formed by it. Now, turn it and find the image formed. Do you find any difference? Find out the reason.

Answer:

Reason :

(i) The curved surface of the spoon acts as a reflecting surface. But this reflecting surface is not flat like that of a plane mirror. Thus the spoon behaves as a curved mirror.

(ii) The inner side of the spoon is referred to as the concave side whereas the back (outer) bulging side is referred to as the convex side.

(iii) You will observe that the image is (inside bowl) always real, inverted and formed on the same side of the object.

(iv) In outside bowl the image is diminished erect and virtual.