text: who likes physics? (6)refraction.  horizontal rays of red light (  , in vacuum) and violet light (  , in vacuum) strike a glass prism perpendicular to a side.  the indices of refraction for the red and violet light in glass are 1.662 and 1.698, respectively.  what is the angle of refraction for each ray as it emerges from the prism?  the prism is in the shape of a right triangle with the top angle being 25 degrees.  (i.e. top angle = 25 degrees, bottom left angle = 90 degrees, bottom right angle = 65 degrees).    answers: 45 degrees, 46 degrees assume that the incident rays are incident normally on the flat side (one of the sides forming the right angle) of the prism. the side opposite to the top angle is the base. when any light is incident perpendicular onto a transparent medium, it is simply transmitted without undergoing any refraction. so, the ray incident on the flat surface normally (means perpendicularly) is transmitted to the slant face containing 65* angle. construct a line perpendicular to this slant face at the point of incidence. you will find that the angle between this line and the light rays is 25*, also known as the angle of incidence. using refractive index = (sine of the angle of incidence/sine of the angle of refraction), we can find the angle of refraction for each colour depending upon its refractive index. the angle of incidence is the same 25* for both the rays. the problem is that the refractive indices given are for light travelling from air medium into glass medium, but, here, the light rays are travelling from the inside of the glass medium to the outside air medium. so, reverse the angles of incidence and refraction so that it looks as if the rays are travelling from the air medium into the glass medium. so, now, the <i is to be found out and <r = 25* u = (sin <i / sin <r), sin <i = (u x sin <r). calculating this, <i for red = 44.62* and <i for violet = 45.857* these are the answers. <i is the angle of incidence and <r is the angle of refraction.  still doubts? visit www.pcmhelp.netfirms.com