wave equation is 



2 •• 



V E = 



£ 



2 



4Tra 



which reduces to 



jj2 _ £00 _ 47rgcjo 



£ is the dielectric constant, and a the conduc 



2 

 it can be seen that the imaginary part of k co 



term to E . The conductivity a = ne[j, where n 



and ji, the ion mobility. For high frequencies ( 



the mobility of heavy ions like Na"*" is approxima 



frequencies, the ions can follow the changes in e 



move. The resulting collisions are taken into ac 



way by putting in the free space wave equation a 



to E . This is the term which leads to absorpti 



An idea of the dependence of the amplitude 

 on frequency and intensity can be gained from the 

 of motion of a free ion is 



tivityo Since E~ e , 



ntributes an absorption 



is the ion density 

 infrared and higher), 

 tely zero. At lower 

 lectric field and thus 

 count in a macroscopic 

 damping term proportional 

 on. 



of motion of the ions 

 following. The equation 



e E = m r 



and the amplitude of its motion is 



r = 



E 



ma) 



The following table gives some numbers based on E = .024 e.s.u. (the value 

 for sunlight). 



5.2x10" 

 5.2x10" 

 5.2x10" 

 5.2x10 



■16 

 ■12 



-4 



10^(.01 cm) 



10^(1 cm, 30,000 mc) 



lOlO (300 mc) 

 10^2 (3 jnc) 



-9- 



