HW3A is over Lectures 29 through 34, which is Wed Nov 19. Stay up to date on lectures early in Unit 3! Thursday, November 27, is Thanksgiving.

29. one point, from Lecture 29, a group question, short explanations

(a) .3 How Small? Each of you pull out a hair and very carefully measure it's thickness (NOT LENGTH!) on a ruler with millimeter markings. I will bring such a ruler to discussion, in case you don't have one. Choose the smallest one in your group. Write in scientific notation, that is, 10^(-something), how small that hair is. (.1) Approximately how many atoms would fit close-packed across that hair? (.1) How many nuclei would fit across the hair (if they were packed next to each other)? (.1)

(b) .3 Seeing Atoms. Three ways to ``see'' that atoms exist are Brownian Motion, Kinetic Theory, and a Scanning Tunneling Microscope (STM), which won a recent Nobel Prize. Describe how each of these gives convincing evidence for atoms. As you are answering this, say if any of the ways makes use of spectroscopy or scattering. (.1 apiece) If you are interested in seeing an STM up close, there's one in a lab under 1300 Sterling. Ask me. I show one in a later TV lecture.

(c) .4 Seeing Electrons. Explain how J. J. Thomson concluded that the electron's mass is 1/2000 the mass of a proton, instead of its charge being 2000 times the charge of a proton. You must describe two pieces of evidence. As you are answering this, say if any of the ways makes use of spectroscopy or scattering. (.2 apiece) There is some choice in what you select.