Problem Set 5


Due October 18


Problem A: The standing waves of a square drumhead are written z = sin(kxx)sin(kyy)sin(2pnt). The length of each side of the drumhead is a.


a. What are the allowed values of kx and ky?

b. Mark the four lowest values of k = (kx2 + ky2)1/2 on the kx-ky plane. Determine n for each. (Call the wave speed v.)

c. Determine the density of states g(k)dk.

d. Determine g(n)dn.

e. Determine g(l)dl.






3-10. b stands for 6pηr.






Problem B: Monochromatic X-rays are incident on a crystal in the geometry shown in Figure 3-16 of the textbook. Assume the surface of the crystal is a (100) plane. The first order Bragg peak is observed when the Bragg angle, q, is 34. The crystal spacing is known to be d = 0.347 nm.


a. What is the wavelength of the X-rays?


Now consider a set of crystal (Bragg) planes that make an angle of 45 with the surface of the crystal.


b. Find the angle between the incident X-rays and the surface of the crystal that produces the first order Bragg peak from this new set of crystal planes.

c. Determine the angle between the scattered X-rays and the surface of the crystal for this case.

d. Sketch a third set of Bragg planes for this crystal.


Extra credit: 4-50