Light 人 light travels through space in straight lines. If a ray of light meets a body in its passage through space,one of three things may happen to it: 1-Absorbtion:opaque materials for example black bodies,absorb the light which falls on them; 2-Reflection;materials such as mirror surfaces,reflect the light backwards; 3-Transmition:transparent materials such as glass,transmit the light;a considerable proportion of it,allowing to pass through them but it's direction will be changed (Refraction). Many substances combine these effects to some degree. In space,light maintains a constant speed of about 186 000 miles per second, but as it travels through the substance of such a transparent body,it will encounter more resistance,this retards its progress. When a beam of light strikes a glass plate with parallel sides,it is retarded while traversing the plate,and then travels on unaffected. 3Light ➢ light travels through space in straight lines. ➢ If a ray of light meets a body in its passage through space, one of three things may happen to it: 1-Absorbtion: opaque materials for example black bodies, absorb the light which falls on them; 2-Reflection; materials such as mirror surfaces, reflectthe light backwards; 3-Transmition : transparent materials such as glass, transmitthe light; a considerable proportion of it, allowing to pass through them but it’s direction will be changed (Refraction). Many substances combine these effects to some degree. 3 In space, light maintains a constant speed of about 186 000 miles per second, but as it travels through the substance of such a transparent body , it will encounter more resistance , this retards its progress. When a beam of light strikes a glass plate with parallel sides, it is retarded while traversing the plate, and then travels on unaffected