no 



LIGHT 



FIG. 60. The ray AC is reflected as CD. 



32 with the 'perpendicular, the path of the reflected ray also 



makes an angle of 32 with 

 the perpendicular. The 

 ray (AC, Fig. 60) which 

 falls upon the mirror is 

 called the incident ray, and 

 the angle which the inci- 

 dent ray (A C) makes with 

 the perpendicular (BC} to 

 the mirror, at the point 

 where the ray 'strikes the 

 mirror, is called the angle 

 of incidence. The angle 

 formed by the reflected ray 

 (CD} and this same per- 

 pendicular is called the angle of reflection. Observation and 

 experiment have taught us that light is always reflected in 

 such a way that the angle 

 of reflection equals the 

 angle of incidence. Light 

 is not the only illustration 

 we have of the law of re- 

 flection. Every child who 

 bounces a ball makes use 

 of this law, but he uses 

 it unconsciously. If an 

 elastic ball is thrown per- 

 pendicularly against the 

 floor, it returns to the 

 sender; if it is thrown 



against the floor at an angle (Fig. 61), it rebounds in the 

 opposite direction, but always in such a way that the angle of 

 reflection equals the angle of incidence. 



\ 



FIG. 61. A bouncing ball illustrates the law of 

 reflection. 



