The heat Capacity of a solid

  • #1
Hello everyone !

I'm a bit confused about assumption that's made in "Concept in Thermal Physics ; Stephen J. Blundell and Katherine M. Blundell" page 205.
It is stated that
" Consider a cubic solid in which each atom is connected by springs (chemical bonds) to six neighbours (one above, one below, one in front, one behind, one to the right, one to the left). Since each spring joins two atoms, then if there are N atoms in the solid, there are 3N springs (neglecting the surface of the solid, a reasonable approximation if N is large). Each spring has two quadratic modes of energy (one kinetic, one potential) and hence a mean thermal energy equal to 2 x 1/2 kT = kT. Hence the mean energy of the solid is
<E> = 3N k T
"
How can it says that the spring has two modes of energy? It is only potential, isn't it? How can the kinetic one arises since spring is actually virtual connector which has no mass?

Also, I'm confused about comparison the number of springs and particles in the system.

Thanks a lot for your helps :):)
 

Answers and Replies

  • #2
Matterwave
Science Advisor
Gold Member
3,966
327
The kinetic energy would be of the atoms that the springs are attached to. The potential energy can be thought of as stored in the springs. :)
 

Related Threads on The heat Capacity of a solid

  • Last Post
Replies
2
Views
2K
Replies
7
Views
12K
Replies
3
Views
2K
Replies
8
Views
658
  • Last Post
Replies
3
Views
3K
  • Last Post
Replies
1
Views
1K
Replies
2
Views
7K
  • Last Post
Replies
28
Views
346
Replies
2
Views
747
  • Last Post
Replies
1
Views
641
Top