WHAT ARE SOME OF THE PROPERTIES OF LIGHT? 137 



Demonstration 1. Law of Reflection. 



Hold a plane mirror in a narrow beam of light in a dark room. 

 The light is bent or reflected from the mirror. We call the incom- 

 ing ray the incident ray and the outgoing ray the reflected ray. A 

 line at right angles to the sur- 

 face where the ray of light meets 

 it is called a normal. Hold a 

 ruler at right angles to the 

 mirror at the point where the 

 beam strikes the mirror, com- 

 pare the angle between the ruler 

 and the beam coming to the 

 mirror (angle of incidence) and 

 the angle between the ruler and 



the beam going from the mirror (angle of reflection). Turn the 

 mirror slightly to change the angles. Compare the angles as 

 before. What do you notice with reference to the angle of in- 

 cidence and the angle of reflection? When light is reflected from 

 a plane surface, how does the size of the angle of reflection com- 

 pare with the size of the angle of incidence? 



How We See in a Mirror. When you look into a mirror, 

 the image appears to be behind it. If you step close to 

 the mirror, the image comes close ; if you step away, the 

 image goes away. If you examine the diagram, you will 

 see that light goes to the eye in the direction it would if 

 the object were really where the image is, but in reality 

 it goes from the object to the mirror, which reflects it to 



If the image is behind the mirror why can you see it ? 



the eye. How does the distance ON compare with the 

 distance O'N f How does the angle / compare with the 

 angle R at N ? AiSf At Tf The image we see is an 



