Physics 2150 Experimental Physics 2 Dmitry Reznik Lecture 1: Introduc@on to Course 1 General Informa@on Lecture instructor: Dmitry Reznik email: [email protected] office hours: by appointment Course Website: hIp://www.colorado.edu/physics/phys2150 Textbook: Taylor, An Introduc+on to Error Analysis 2 Modern Physics: Physics of the 20th century Goals of the course: 1.  To get a “hands-­‐on” experience with modern physics 2.  To learn the physics behind the experiments in depth 3.  To learn how to take and record data. 4.  To learn how to report experimental results 5.  To learn how to work with different partners 6.  To appreciate how surprisingly simple experiments can see quantum nature of the world around us. This week’s reading Before next lecture 1. Read: Syllabus (website) Instruc@ons for Wri@ng Lab Reports (website) Ch. 5 in Taylor 2. Fill out Part I of the survey (Web site) You will get 2 points for doing Part I and 2 points for Part II at the end of the c4 ourse Prerequisites Physics 1140 Physics 2130 or 2170. Coenrollment is OK. Familiarity with numerical calcula@on program (Mathema@ca, etc.) Online radioac@ve materials handling training (to be completed by the end of next week. Go to the course home page for links) Grading •  Lab reports: 120 points •  Homework: 12 points •  Survey: 4 points (2 points for part I in the beginning of the semester, 2 points for part II at the end). Grades of each TA to be curved separately. Mean will be about B/B-­‐ You will choose 6 out of 12 experiments Charge-­‐to-­‐Mass Ra@o of the Electron Here we make electrons fly in a circle in a uniform magne@c field and figure out its charge-­‐
to-­‐mass ra@o from the field strength, the radius of the orbit, and its velocity. The Millikan Oil Drop Experiment The first accurate measurement of the electron’s charge. Millikan found that droplets of oil from a simple spray boIle usually carry a net charge of a few electrons. By observing how these drops fly under the influence of electric field, he was able to get an accurate es@mate of the charge of the electron. R.A. Millican, Nobel Prize 1923 Michelson’s interferometer Allows incredibly accurate measurements of lengths using light (accuracy: ~10-­‐7 m) 0
Rest Mass of the K Meson K0 Meson is a subatomic par@cle consis@ng of d quark and an s ̄ an@quark. We will use a Einstein’s theory of rela@vity to analyze bubble-­‐chamber photographs of K0 Meson decay into pions. The photoelectric effect This is one of the most famous experiments that ushered in the era of quantum physics. Albert Einstein was awarded the Nobel prize for developing the quantum theory of this effect, which was later confirmed by experiments of Robert Millican. The Compton Effect Demonstrates that momentum of photons is propor@onal to the inverse of its wavelength and that photons can collide with electrons like billiard balls Arthur Holly Compton Nobel prize 1927 Electron Diffrac@on from Crystals Proves the idea of DeBroglie that electrons can diffract like waves Louis de Broglie, Nobel Prize 1929 Emission Spectra and the Balmer Series Emission spectra and the Balmer series was a key experimental clue to how electrons behave in atoms. Johann Jakob Balmer The Franck-­‐Hertz Experiment First electrical measurement to clearly show the quantum nature of atoms James Franck Gustav Hertz Nobel Prize 1925 220
Radioac@ve Decay of Rn The two objec@ves of this experiment are: To determine the half-­‐life of the radioac@ve gas 220Rn (Radon) To es@mate the half-­‐life of the 232Th (Thorium) Magne@c Torque You will study how a magnet moment μ interacts with a magne@c field B and how the orbital angular momentum interacts with Earth’s gravity. The Hall Effect Effect of magne@c field on electric current. Can be used to probe the sign of charge carriers in metals and semiconductors. Edwin Hall Measurement Uncertainty We will con@nue to refine our understanding of how to es@mate uncertainty in your measurements that we started in 1140. As used by physicists, “error” is a synonym for “uncertainty”. It is dis@nct from “discrepancy” or “mistake”. A result is meaningless without an uncertainty. ALL results should be quoted or recorded in your lab notebook with an error! The uncertainty can result from inaccurate equipment, limited sta@s@cs, or other factors beyond your control. Uncertain@es should have 1 significant digit. The measurement result should have the same final digit as the uncertainty: Bad: Good: 1.41±0.7 1.41±0.07 6.7±0.04 6.7±0.4 0.1006±0.00083 0.1006±0.0008