HOW DO I USE LIGHT? 



131 



who walk by the window outside will reflect rays of light 

 so that images of them appear on the wall opposite the 

 window. A curious thing about the image is that it is 

 upside down. If we make a pinhole in one end of a small 



fround 

 glass- 



How many devices can you name that involve the principle shown here ? 



box and have a shaded frosted glass in the opposite end, 

 we can see on the frosted glass an inverted image of a 

 bright object that is in front of the pinhole. 



The diagram will help us to understand this. A is seen 

 by light that comes from A. The light that goes through 

 the pinhole will fall at A'. The light from B will reach the 

 frosted glass at B'. Light from all points between A and 

 B will fall somewhere between A' and B'. The image is 

 inverted because the rays which come from the object 

 cross where they pass through the pinhole. If the hole 

 were not very small and other light was not kept out, 



there would be such overlapping of light from different 

 parts of the object that no clear image could be seen. 

 This principle of image formation is used in our eyes when- 

 ever we look at any object. There is one difference. 

 There is a lens at the opening of the eye. This allows 

 more light to come in and gives a brighter image. The 



