College Physics Labs - Electricity and Magnetism

Introduction

Introduction, Policies, and Procedures
- Lab Enrollment
  
  You must be officially registered through the Registrar's Office for the Physics lab section you attend; otherwise you may not receive credit for the entire Physics course...
- Lab Attendance and Missed Labs
  
  You are expected to attend all scheduled labs that correspond to your physics course...
- Goals of the Introductory Physics Labs at UNC-CH
  
  The Art of Experimentation: The introductory laboratory should engage each student in significant experiences with experimental processes and design...
- Preparation for Lab and Pre-Lab Assignments
  
  Study the experiment you will be performing before you come to lab...
- What to bring to lab
  
  Lab manual, Laboratory data sheets, Pre-lab assignment, Scientific calculator (preferably with statistical functions), A pen...
- Laboratory Work
  
  At the beginning of each lab, your instructor will spend 15 to 20 minutes giving an overview of the experiment you will perform...
- Lab Reports
  
  Lab reports must be typed or printed clearly in ink. Each report must include a cover page, an abstract, a summary of your experimental results (including your original data sheet and any additional notes, tables, or graphs), and a discussion of your findings...
- Lab Report Submission and Deadlines
  
  Lab reports are generally due at the next lab period after the experiment is performed; however your lab instructor may be able to give more immediate feedback if you submit your report before your next lab session (this is particularly encouraged for the first lab report)...
- Lab Report Grading
  
  Reports are graded on a 100-point scale as follows...
- Lab Grades
  
  Lab scores are reported to your physics course instructor, who counts it as part (usually 25%) of your overall course grade...
- Lab Exam
  
  A physics laboratory practicum is administered near the end of the semester and counts as 20% of your final lab average...
- Laboratory and the Honor Code
  
  The Department of Physics and Astronomy fully supports the Code of Student Conduct, as expressed in the document "The Instrument of Student Judicial Governance for the University of North Carolina at Chapel Hill" (1991)...
- Safety
  
  Always keep safety in mind when working in a laboratory situation...
Lab Expectations
- Assignments
  
  Lab assignments are common for all students taking the lab...
- Expectations of a Physics Lab Student
  
  A procedure will not be provided for you, and no printers are available in the lab rooms...
- Grading
  
  Each lab consists of a PreLab and LabReport assignment...
- Plagiarism and Working Together
  
  Complete all WebAssign free-response questions in your own words...
- Attendance
  
  Arrive on time, if you are more than 10 minutes late for your scheduled lab, you may be asked to leave and you may not be able to make up the lab...
Concepts Survey
- Concepts Survey
  
  A concepts survey is administered at the beginning and end of the semester to see how much each student has learned...
Measurements and Error Analysis
- The Uncertainty of Measurements
  
  Some numerical statements are exact: Mary has 3 brothers, and 2 + 2 = 4...
- Types of Errors
  
  Measurement errors may be classified as either random or systematic, depending on how the measurement was obtained (an instrument could cause a random error in one situation and a systematic error in another)...
- Estimating Experimental Uncertainty for a Single Measurement
  
  Any measurement you make will have some uncertainty associated with it, no matter the precision of your measuring tool...
- Estimating Uncertainty in Repeated Measurements
  
  Suppose you time the period of oscillation of a pendulum using a digital instrument (that you assume is measuring accurately) and find: T = 0.44 seconds...
- Standard Deviation
  
  To calculate the standard deviation for a sample of N measurements: Sum all the measurements and divide by N to get the average, or mean...
- Standard Deviation of the Mean (Standard Error)
  
  When we report the average value of N measurements, the uncertainty we should associate with this average value is the standard deviation of the mean, often called the standard error (SE)...
- Anomalous Data
  
  The first step you should take in analyzing data (and even while taking data) is to examine the data set as a whole to look for patterns and outliers...
- Fractional Uncertainty Revisited
  
  When a reported value is determined by taking the average of a set of independent readings, the fractional uncertainty is given by the ratio of the uncertainty divided by the average value...
- Propagation of Uncertainty
  
  Suppose we want to determine a quantity f, which depends on x and maybe several other variables y, z, etc...
- The Upper-Lower Bound Method of Uncertainty Propagation
  
  An alternative, and sometimes simpler procedure, to the tedious propagation of uncertainty law is the upper-lower bound method of uncertainty propagation...
- Significant Figures
  
  The number of significant figures in a value can be defined as all the digits between and including the first non-zero digit from the left, through the last digit...
- Use of Significant Figures for Simple Propagation of Uncertainty
  
  By following a few simple rules, significant figures can be used to find the appropriate precision for a calculated result for the four most basic math functions, all without the use of complicated formulas for propagating uncertainties...
- Uncertainty, Significant Figures, and Rounding
  
  For the same reason that it is dishonest to report a result with more significant figures than are reliably known, the uncertainty value should also not be reported with excessive precision...
- Combining and Reporting Uncertainties
  
  In 1993, the International Standards Organization (ISO) published the first official worldwide Guide to the Expression of Uncertainty in Measurement...
- Conclusion: "When do measurements agree with each other?"
  
  We now have the resources to answer the fundamental scientific question that was asked at the beginning of this error analysis discussion: "Does my result agree with a theoretical prediction or results from other experiments?"..
- References
  
  Baird, D.C. Experimentation: An Introduction to Measurement Theory and Experiment Design, 3^rd. ed. Prentice Hall: Englewood Cliffs, 1995...
Data Analysis
- Using Excel for Data Analysis
  
  This tutorial will lead you through the steps to create a graph and perform linear regression analysis using an Excel spreadsheet...
Measuring Instruments
- Calipers
  
  The Vernier Caliper and the Micrometer Caliper, pictured here, are instruments for making precise measurements of length...
- Balances
  
  The balance you will use in the laboratory is a modern, digital balance...
- The Smart Timer
  
  In many of the exercises in this manual, you will be called upon to measure time intervals and frequencies (number of events occurring in a given time interval)...
Graphing Techniques
- Graphing Techniques
  
  The construction of graphs is a very important technique in experimental physics...
Introduction to Electronic Equipment
- Introduction
  
  This semester you will be exploring electricity and magnetism. In order to make your time in here more instructive we've designed this laboratory exercise to introduce you to some of the equipment you'll be using in this course...
- Part 1. Measuring Voltage, Current, and Resistance with a Digital Multimeter
  
  Three different multimeters are provided for this lab: the Fluke 77, the Radio Shack, and the Tenma...
- Part 2. Measuring Voltage with an Oscilloscope
  
  This part of the lab will be very similar to part 1 in that you'll be measuring voltage from a simple DC circuit...

Laboratories

Electric Fields and Potentials
- Introduction
  
  This experiment is intended to illustrate the concepts of electric fields and electric potentials and how they are related to the charge distribution that produces them...
- Procedure
  
  In this experiment you will determine the equipotential surfaces around several different charge configurations: "parallel lines", a "line and triangle" and "concentric circles"...
- Data Analysis
  
  You will now graphically analyze the quantitative data that you obtained in the section Parallel Lines Configuration - Quantitative...
- Discussion
  
  Now that you have sketched predictions and graphed your data, summarize your findings...
Ohm's Law and Electrical Circuits
- Introduction
  
  In this experiment, you will measure the current-voltage characteristics of a resistor and check to see if the resistor satisfies Ohm's law...
- Procedure
  
  Using the multimeter as an ohmmeter, measure and record the resistances of each of the three resistors provided...
- Data Analysis
  
  For this part we shall denote the calculated equivalent resistance by R_T, and the measured equivalent resistance by R...
- Discussion
  
  Summarize the results for the section on Resistance Measurements...
The RC Circuit
- Introduction
  
  The goal in this lab is to observe the time-varying voltages in several simple circuits involving a capacitor and resistor...
- Procedure
  
  Fully discharge your capacitor. Measure the capacitance of your capacitor using the capacitance meter provided by your instructor...
- Analysis
  
  Make a plot of ln(V_C/V₀) vs. t from the data obtained in Part 1...
- Discussion
  
  For both parts of the experiment, compare the value of the time constant obtained to the predicted value, computed from the known values of R and C...
- The Oscilloscope
  
  The oscilloscope is such an important tool for scientists that learning how to use one is a major goal of this laboratory...
Determination of e/m for the Electron
- Introduction
  
  In this experiment you will measure e/m, the ratio of the charge of an electron to the mass of an electron...
- Procedure
  
  Connect the apparatus according to the arrangement shown in Fig. 1 and start taking data following the steps outlined below...
- Analysis
  
  An important modification must be made to Eq. 6 before it can be used to calculate e/m...
- Discussion
  
  Compare your experimental value of e/m to the accepted value...
Reflection, Refraction and Polarization
- Introduction
  
  When a ray of light strikes the surface of a piece of transparent material the beam is split—part of the beam is reflected from the surface, while the rest is transmitted into the material...
- Procedure
  
  The apparatus for this experiment (shown in Fig. 4) consists of a He-Ne laser light source, an optics bench, a ray table and ray table base, an acrylic semi-circular disk, a ray table component holder, and a polarizer...
- Data Analysis
  
  In this part of the experiment, you will analyze the data from Table 1 to verify if Snell's Law is satisfied and if so, derive the index of refraction of acrylic...
- Discussion
  
  Summarize the index of refraction derived from Parts 1, 2, and 3...
Thin Lenses and Lens Systems
- Introduction
  
  When light from an object passes through a lens, an image of the object is generally formed...
- Procedure
  
  A lens is primarily characterized by its focal length, so it is worthwhile learning how to measure the focal length of a lens...
- Analysis
  
  Be sure to characterize the uncertainty of your measurements so that you can judge whether they do or do not agree with your theoretical predictions...
- Discussion
  
  Discuss the results from each part of the experiment and evaluate whether the results were consistent with the predictions you made...
Measuring the Rydberg Constant
- Introduction
  
  In this experiment, you will observe the visible wavelengths of light produced by an electric discharge in helium gas, using a diffraction grating...
- Procedure
  
  Caution: Use extreme caution around the discharge tube power supply...
- Analysis
  
  For each helium wavelength, calculate the average distance between the discharge tube and the first order images using the following equation...
- Discussion
  
  Summarize your results for the value of grating spacing and the Rydberg constant (both their values and their uncertainties)...
The Photoelectric Effect and the Quantization of Light
- Introduction
  
  When a light with a sufficiently high frequency shines on a metal plate, electrons are ejected from the plate...
- Procedure
  
  The apparatus should be mostly assembled when you arrive. You may, however, need to check focus and alignment and adjust these as needed...
- Analysis
  
  Make a scatter plot of V vs. f from the data collected in Part 3...
- Discussion
  
  Summarize your experimental results for the intensity dependence of the stopping potential...
Radioactivity
- Introduction
  
  The most common form of radiation is the electromagnetic wave...
- Part 1: Radioactivity and the Inverse Square Law
  
  To study the dependence of gamma-ray intensity on distance from a point source. ..
- Part 2: Radioactivity and Shielding
  
  The aim of this experiment is to measure the effect that shielding has on the gamma-ray intensity of the cesium source...
- Part 3: Half-Life of Barium-137m
  
  The aim of this experiment is to measure the effect that shielding has on the gamma-ray intensity of the cesium source...

Introduction

Laboratories

Appendix

Instrument Accuracy