(a) A mobile phone lies along the principal axis of a concave mirror. Show, with the help of a suitable diagram, the formation of its image. Explain why magnification is not uniform. (b) Suppose the lower half of the concave mirror's reflecting surface is covered with an opaque material. What effect this will have on the image of the object? Explain.
(a) Formation of image by the concave mirror is shown in the figure below:
The magnification of each part of the mobile phone is not uniform. The part of the mobile phone at centre of curvature will form image of the same size.
The part that lies between C and F will form an enlarged image beyond C as shown in the fig. above.
Since, the nature of the image is not the same at all sections of the principal axis, magnification varies.
(b) If lower half of the concave mirror is covered with an opaque material, the size of the image will not vary. But, since the reflecting surface has been reduced, the intensity of the image will be less. That is, brightness of the image will decrease.
