GE 226 Introduction to Experimental Labs. Stan Shadick, Lab Co-ordinator

Transcription

1 GE 226 Introduction to Experimental Labs Stan Shadick, Lab Co-ordinator

2 Stan Shadick s Contact Information Office: Room Physics Building Phone: stan.shadick@usask.ca If you are sick or cannot attend a lab due to an emergency, then contact Stan ASAP to arrange to make up lab.

3 Purposes of Experimental Labs Learn how to operate lab instruments and equipment that you may use in your careers. Learn how to apply in a lab scenario the physics concepts discussed in lectures. Learn how to properly format a report of a laboratory investigation or engineering test.

4 Materials Needed for Experimental Labs Copy of lab report pdf files available from lab or course homepage on PAWS. Notebook with ¼ inch graph paper grid or Engineering Problem Paper in a Duotang Scientific Calculator Geometry Set Pen

5 First Experimental Lab M20 First Experimental Lab M20 meets in Room 125 Physics Lab Sections L02, L06 and L10 meet on Jan 10, 11 and 12 respectively Lab Sections L04 and L08 meet on Jan. 17 and 18 respectively. Wed. Lab section L06 meets at 2:00 pm All other lab sections meet at 2:30 pm.

6 Prelab During the week before your scheduled lab, complete the following sections of your lab report: OBJECT THEORY PROCEDURE Data Tables without measurements in DATA section Determine error formulae to be used in report

7 Lab Schedule Lab Schedule pdf file may be found in the files section of your GE226 Webpage. Before midterm break, Lab sections L04 and L08 do their lab 1 week after Lab sections L02, L06 and L10. After midterm break, Lab sections L02, L06 and L10 do their lab 1 week after Lab sections L04 and L08. No labs Feb. 21 March 1.

8 GE226 Lab Schedule 2012 Month T W Th ROOM LAB Jan M20 L02 L06 L10 Moment of Inertia (Torsion.Pend.) Jan M20 L04 L08 Moment of Inertia (Torsion.Pend.) Jan M50 L02 L06 L10 Atwood s Machine Jan/Feb M50 L04 L08 Atwood s Machine Feb M61 L02 L06 L10 Angular Acceleration Feb M61 L04 L08 Angular Acceleration Feb No Labs (Midterm Break) Feb/Mar No Labs Mar M63 L04 L08 Energy Conservation Mar M63 L02 L06 L10 Energy Conservation Mar M62 L04 L08 Angular Momentum Conservation Mar M62 L02 L06 L10 Angular Momentum Conservation

9 Lab Policies Prelab must be done prior to Start of Lab. Anyone who forgot their lab notebook or who does not have their prelab completed or who is more than 5 minutes late will lose 20% of their grade on that lab. Lab Notebooks must normally be submitted before the end of your lab (4:50 or 5:20). Lab Notebooks may be picked up from the GE226 shelf in Room 132, 1 week after lab.

10 NO FOOD OR DRINKS IN LABS For safety reasons due to presence of high voltage equipment and radioactive sources in labs, NO FOOD OR DRINKS of any kind are allowed in lab rooms. Coffee must be consumed before entering lab rooms. You may leave your lunch in your backpack.

11 GE226 Lab Exemptions Anyone who is repeating GE226 and took it during the past 3 years may qualify for a lab exemption if their lab average was 70% or greater. If you wish to apply for a lab exemption, stan.shadick@usask.ca today and indicate the year (and day if you remember) that you previously took these labs. I will reply by after I have looked up your grades.

12 Lab Report Format This format will be used for your labs in the following courses GE124 GE125 GE 226

13 Write your report Neatly In Ink In a Graph Notebook Start each lab report on the top of a new page

14 Lab Report Format Sections Title Object Theory Procedure Data Analysis Conclusion Sources of Error

15 Title Indicate the title of the Experiment at the top of the page In the top right corner, indicate Your Name Partner Partner s Name Date

16 OBJECT Print Object Heading and then write 1 or 2 sentences describing purpose of experimental test Sample: OBJECT: The purpose of this lab is to test whether the vector sum of all forces and torques acting on an object at rest is zero.

17 THEORY Write in Paragraph form starting with Theory heading. Discuss any significant equations or physical concepts or laws that pertain to experiment. Derive any formulae required. Add a chart defining all variables clearly. Include a labelled sketch of apparatus.

18 PROCEDURE If procedure is described in instruction file, then you only need to write: Procedure See GE 226 instruction file. Describe any changes to procedure in this section.

19 DATA (or OBSERVATIONS) Add Title and Table Number to each table Label Column Headings Clearly Include units in Column headings to avoid repetition in column cells Use Metric Units Either: SI units (m, kg, s and derived units e.g.: N, J) or cgs units (cm, g, s and derived units e.g. dyne, erg)

20 DATA (or OBSERVATIONS) Include Errors in Column Heading if errors are the same for all column entries If errors are different for each entry, then include error in each table cell Express Error and Value in same units, same power of 10 and same number of decimal positions

21 DATA (or OBSERVATIONS) Tabulate clearly and directly all measurements in ink NEVER Erase Data Make table cells large enough that there is room to cross out incorrect measurements and record corrected values

22 Sample Data Table Table 1: Initial Momentum and Energy Data for Red Car Trial Mass, M Velocity, V Momentum, P Kinetic Energy, E (kg) (X 10 2 m/s) (kg m/s) (J) ± kg ± ± ± 1.2

23 ANALYSIS Include Sample Calculations and Graphs

24 ANALYSIS Sample Calculation Format Include one sample calculation for every computation in lab Title each sample calculation Use 1 full line for each step (Don t set up columns)

25 ANALYSIS Sample Calculation Format Title Statement of Values Equation in symbols Substitution of Data into Formula with units Calculation Result with Units (Calculate both numerical answer and final units)

26 ANALYSIS Sample Calculation Format Sample Calculation of Initial Momentum of Red Car M = ± kg V = (2.0 ± 0.3) X 10 2 m/s P = (1/2)MV 2 P = (1/2)( kg)(2.0 X 10 2 m/s) 2 P = 2.0 X 10 4 kg m 2 /s 2 Disagrees with proper units for momentum!

27 ANALYSIS Sample Calculation Format Sample Calculation of Initial Momentum of Red Car M = ± kg V = (2.0 ± 0.3) X 10 2 m/s P = (1/2)MV 2 P = (1/2)( kg)(2.0 X 10 2 m/s) 2 P = 2.0 X 10 4 kg m 2 /s 2 P = 2.0 X 10 2 kg m/s

28 Why is this a poor graph? Graph 1: Elapsed Time versus Velocity Velocity (m/s) Slope = V/ t =(74.0m/s 68.0 m/s)/(0.60s 0.42s) = m/s Elapsed Time (s)

29 Problems with this Graph Slope = V/ t =(74.0m/s 68.0 m/s)/(0.60s 0.42s) = m/s 2 Graph 1: Elapsed Time versus Velocity Velocity (m/s) Elapsed Time (s) Poor Title: Title should describe purpose of Graph Also: It is a graph of Velocity vs. Elapsed Time X-axis Difficult to Interpolate: Label multiples of 2,4,5 divisions on each axis. Extra Decimal Place on labels is unnecessary Most of Graph is Empty Space Adjust Scale to fit range of data Slope Calculation has wrong number of Sig Figs.

30 Proper Graph Graph 1: Acceleration of Red Car Velocity (m/s) Elapsed Time (s) Slope = V/ t =(84.0 m/s 59.0 m/s)/(0.860s 0.160s) = 35.7 m/s 2

31 Error Bars Graph 1: Acceleration of Red Car Velocity (m/s) Elapsed Time (s) The vertical error bars plotted indicate that the Velocity is measured to ±5 m/s.

32 Percentage Difference Calculation % Difference in P = Experimental Value Known Value Known Value X100% = Initial Value Final Initial Value Value X100% = L arg est Value Smallest Smallest Value Value X100%

33 Conclusion The Conclusion is the most important section of your lab report. Write in Paragraph Form. The conclusion must be completely self-explanatory so that anyone can understand your conclusion without reading any of the earlier portions of your report. Ensure that you review your Object statement and address those questions in the Conclusion.

34 Conclusion If there are few numerical results, the first paragraph should state these results including units and their experimental error values. If there are many numerical results, include a table of results with units and experimental errors. To save time, you may include a sentence that refers to a previous page of your report where you have tabulated these values. Intermediate results need not be mentioned.

35 Conclusion In a second paragraph discuss the implications of your results. For example, do your results verify any physical laws or constants or formulae? If so, describe which ones and justify your reasoning.

36 Sources of Error Write in paragraph form. Clearly describe every potentially plausible systematic (non-measurement) error and describe their expected qualitative effects on your results.

37 Sources of Error Consider potential errors caused by problems with Equipment Theory Procedure

38 Example Source of Error Air Friction acting on the puck could reduce its speed after the collision and hence could lower its final kinetic energy. This error could explain why the final kinetic energy was less than the initial kinetic energy in the inelastic collision.

39 General Tips Explain yourself CLEARLY. Always include UNITS. Write NEATLY. Follow correct Canadian SPELLING.