135-138] 



Boundary Conditions 



123 



138. 



follows : 



Refraction of the lines of force. 

 From the continuity of the tangential components of intensity, it 



(i) that the directions of R l and R 2 , the intensities on the two sides of 

 the boundary, must lie in a plane containing the normal, and 



(ii) that 



sn e = 



sn e 



Combining the last relation with equation (68), we obtain 



KI COt 6 t = K z COt 6 2 



(71). 



From this relation, it appears that if K l is greater than K 2 , then e x is greater 

 than e 2 , and vice versa. Thus in passing from a smaller value of K to a 

 greater value of K, the lines are bent away from the normal. In illustration 

 of this, fig. 43 shews the arrangement of lines of force when a point charge 

 is placed in front of an infinite slab of dielectric (K 7). 



FIG. 43. 



