GOALS

Physics

• Demonstrate that accelerated electrons have an effective wavelength, , by diffracting them from parallel planes of atoms in a carbon film.
• Measure the spacings between two sets of parallel planes of atoms in carbon.

Techniques

• Control the wavelength of the electron beam by varying the accelerating voltage.
• Use the De Broglie expression for the wavelength of the electrons and the Bragg condition for analyzing the diffraction pattern.

Error

• Calculating the uncertainties in the data points on your graph gives you a good opportunity to use the principles of error propagation.

Question (work out in lab book before class)

1. Derive an expression for the extrapolated value of the diffraction ring of diameter D' shown in Fig. 12.

References

• Wehr, Richards, and Adair; 6.9, 7.1-7.4.
• Halliday and Resnick; 43.1.