Lecture Video: Translation Symmetry
Prof. Lee introduces the concept of “boundary conditions” which enables us to solve a finite system using the general solution of an infinitely long system. In the end of the lecture, a wave equation is derived in the continuous limit.
Chapter 5: Waves (PDF - 1.4MB) (section 5.3 to end)
Chapter 6: Continuum Limit and Fourier Series (PDF - 1.2MB) (through section 6.1)