Light – Reflection and – 9 PDF Past Paper

n Try with plane mirrors of different sizes. Did you see the entire object in the image? n Repeat this Activity with a concave mirror. Did the mirror show full length image of the object? n...

n Try with plane mirrors of different sizes. Did you see the entire object in the image? n Repeat this Activity with a concave mirror. Did the mirror show full length image of the object? n Now try using a convex mirror. Did you succeed? Explain your observations with reason. You can see a full-length image of a tall building/tree in a small convex mirror. One such mirror is fitted in a wall of Agra Fort facing Taj Mahal. If you visit the Agra Fort, try to observe the full image of Taj Mahal. To view distinctly, you should stand suitably at the terrace adjoining the wall. Uses of convex mirrors Convex mirrors are commonly used as rear-view (wing) mirrors in vehicles. These mirrors are fitted on the sides of the vehicle, enabling the driver to see traffic behind him/her to facilitate safe driving. Convex mirrors are preferred because they always give an erect, though diminished, image. Also, they have a wider field of view as they are curved outwards. Thus, convex mirrors enable the driver to view much larger area than would be possible with a plane mirror. Q U E S T I O N S ? 1. Define the principal focus of a concave mirror. 2. The radius of curvature of a spherical mirror is 20 cm. What is its focal length? 3. Name a mirror that can give an erect and enlarged image of an object. 4. Why do we prefer a convex mirror as a rear-view mirror in vehicles? 9.2.3 Sign Convention for Reflection by Spherical Mirrors While dealing with the reflection of light by spherical mirrors, we shall follow a set of sign conventions called the New Cartesian Sign Convention. In this convention, the pole (P) of the mirror is taken as the origin (Fig. 9.9). The principal axis of the mirror is taken as the x-axis (X’X) of the coordinate system. The conventions are as follows – (i) The object is always placed to the left of the mirror. This implies that the light from the object falls on the mirror from the left-hand side. (ii) All distances parallel to the principal axis are measured from the pole of the mirror. (iii) All the distances measured to the right of the origin (along + x-axis) are taken as positive while those measured to the left of the origin (along – x-axis) are taken as negative. (iv) Distances measured perpendicular to and above the principal axis (along + y-axis) are taken as positive. (v) Distances measured perpendicular to and below the principal axis (along –y-axis) are taken as negative. 142 Science 2024-25