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www.GOALias.blogspot.comWhy are concave and convex mirrorscalled spherical mirrors?Take a rubber ball and cut aportion of it with a knife or a hacksawblade [Fig. 15.13 (a)]. (Be careful.Ask an elder person to help you incutting the ball). The inner surfaceof the cut ball is called concave andthe outer surface is called convex(Fig. 15.13 (b)).Convex surface(a)Fig. 15.13 A spherical mirror is a part of asphereThe inner surface of a spoon acts likea concave mirror, while its outer surfaceacts like a convex mirror.We know that the image of an objectformed by a plane mirror cannot beobtained on a screen. Let us investigateif it is also true for the image formed bya concave mirror.Activity 15.6CAUTIONConvex surface(b)You will conduct Activity 15.6 in thesunlight. Be careful, never lookdirectly towards the sun or its imageas it may damage your eyes. You maylook at the image of the sun when itis thrown on a screen or a wall.Fig. 15.14 A concave mirror forms a real imageof the sunTake a concave mirror. Hold it facingthe sun. Try to get the light reflected bythe mirror on a sheet of paper. Adjustthe distance of the paper until you get asharp bright spot on it (Fig. 15.14). Holdthe mirror and the sheet of paper steadyfor a few minutes. Does the paper startburning?This bright spot is, in fact, the imageof the sun. Notice that this image isformed on a screen. An image formedon a screen is called a real image.Recollect that in Activity 15.2 the imageformed by a plane mirror could not beobtained on a screen. Such an image iscalled a virtual image.Now let us try to obtain on the screenthe image of a candle flame formed by aconcave mirror.Activity 15.7Fix a concave mirror on a stand (anyarrangement to keep the mirror steadywould do) and place it on a table(Fig. 15.15). Paste a piece of white paperon a cardboard sheet (say about180SCIENCE