678 Prof. B. M. Sen on the Kinetic Theory of Solids 

 For a gas such as oxygen, 



Cp = -2'4, 7 -l-4; 



Energy absorbed by each molecule for 1° rise of temper- 

 ature 



= j^,J = 3-74 xlO" 16 , 



whereas the external kinetic energy is increased by 

 * = 2-02xl0- 16 . 



In the Kinetic Theory of Gases this difference is explained 

 by the diatomic nature of the molecules, there being no 

 intermolecular forces *. A portion may also be accounted 

 for by the absorption by the electrons. But for solids the 

 matter is complicated by the presence of intermolecular forces 

 against which work has to be done by the heat expansion. 



For a solid we assume that the total energy imparted is 

 split up into three portions : — 



(1) a quantity ol absorbed in increasing the external 

 kinetic energy Q = p[V 3 = a0, where * = 2-02 x 10" ,6 r 

 and 6 the temperature. 



(2) a quantity B absorbed in increasing the kinetic 



energy of rotation relative to the centre. This is 

 presumably absorbed by the electrons in the outer 

 rings. We take 



V = A + B0 = ±n.mv 2 , 



where A represents the store of energy, n the number 

 of electrons taking part in the absorption, m the mass 

 of an electron for velocities small in comparison 

 with that of light, and v the velocity. 



(3) a quantity /5 absorbed in increasing the potential 



energy of the molecules, i. e. in doing work against 

 the inter-molecular forces. 



W9 



... « +/ 3 + B=— J, 



€ 



Taking P1V 2 = «6> for Cu at 0=17° C„ 



V=3-7xl0\ 



Thus for metals at ordinary temperatures V is of order 10 4 . 

 A table of values is given for solids and gases. It may 



* Jeans, i Dynamical Theory of Gases/ art. 270. 





