Laboratory Reports  Home


Rules for Emailing of Lab Reports and Assignments
  1. Only one file per assignment. If you used Excel at all, this means you must include all the information in a single Excel document. Otherwise Word might be used.
  2. Name your file by "YourName-subject-assignment.xls".  (For example: JohnSmith-MEM23061A-hounsfield.xls, or JSmith-testing-ass3.xls,  etc )
  3. Your email must have your name in the subject.
  4. If multiple assignments to be submitted, attach them all in a single email.
  5. Do not resend assignments without permission.


The Lab report should include the following: 

1. Aim: First you should give the aim of the investigation. It should be clear and concise.  

2. Prediction and theory: State the hypothesis or prediction of the investigation. The hypothesis needs to be very clear, giving an exact and complete description of what might happen (and why). The prediction is written like: If …then… You can also give a general background to the study, theory like formulas etc, but keep it brief. Here you should present the different variables. The independent variable is the one that you alter throughout your experiment. For an example, if you are doing a tensile tst, the force is an independent variable, the amount of stretch is a dependent variable. A controlled variables are the ones that you try to keep constant throughout your experiment. Temperature might be an example, or rate of loading of the specimen is a better example. 

3. Materials and methods Give a list of all the equipment used in the experiment. A diagram is usually needed. Describe the method (what you did). Write how the controlled variables were controlled. Write how you made that measurements.
  
4. Lab Results:  List all the measurements, readings etc, in their original numbers, including bad readings. Us a table. Titles, units and the error should be given in the headings of the tables.  

5. Data Processing and presentation: The data should be processed (calculated) correctly and presented in tables (as above) and graphs.  If you use graphs, they should have a caption in which you describe the contents of the graph. The axes of the graphs have to be labelled with units and the points have to be plotted correctly. Make sure that you use the correct type of graphs.  For HL: Error analysis should be carried out if possible (calculate the percentage uncertainty, etc) - see below.
 
6. Conclusion and Evaluation: Write a conclusion based on an interpretation of the results. Compare your results with literature values if possible. Evaulate the methos - weakness of the method used or equations etc. Conclude about the source of error, but don’t include personal mistakes. Suggest real improvements (that can be carried out in the lab) to the investigation. Discuss further investigations that could be carried out.
 

Error Analysis

Record the absolute error for each measurement: The absolute error is the sum of several factors:

Absolute error = (Resolution / 2) + (Parallax error) + (misalignment error) + (systematic error)

Where: Resolution Error = smallest increment in the measurement scale. The human limit is considered to be half of this again. For example, this dial gauge has smallest increment = 0.01mm, so it is considered to be readable to 0.005mm.

Parallax error is an error caused by viewing the meaurement at an angle. Parallax is an apparent displacement or difference of orientation of an object viewed along two different lines of sight. This is why the passenger in a car thinks you are going over the speed limit, but from the driver's view, the needle says the car is going the right speed! Parallax is avoided by looking straight-on, and also kept to a minimum by keeping the needle close to the scale. Your estimate of parallax error depends on the geomtery of the measurement, but for the gauge above the parallax error would be only about 10% of the increment.

Misalignment error: Not taking the measurement parallel or perpendicular. Eg.The dial gauge is not vertical, the tape measure is at an angle, the caliper is not perpendicular etc. This is not supposed to happen if you take the measurement carefully, but some meaurements are more difficult than others. 

Systematic error: An error inherent in the measuring instrument itself. Eg a tape measure is inaccurate due to temperature change, or it is actually printed wrong! Hopefully this is not a problem, but the only way top check is to check the calibration against a known standard.

Calculating with Errors

There are two ways to specify error - absolute and relative ( %).
50 +/- 5mm  has an absolute error of 5mm, and a relative arror of 10%.
When measurements are added or subtracted, the absolute error is added.
When measurements are multiplied or divided, the relative error is added.

Example: Determine the absolute error in calculating the area of a rectangle 100 x 200 mm if the absolute error of the measuring instrument is 10mm.
Area = 100 (10%)  x  200 (5%)  = 20000 (15%)
So absolute error is 15% x 20000  =  3000
In other words, the area is somewhere between 17000 and 23000 sq mm.

You must specify the absolute error when you state your answers.  

Links for information about scientific errors
http://instructor.physics.lsa.umich.edu/ip-labs/tutorials/errors/vocab.html
http://dwb.unl.edu/Teacher/NSF/C14/C14Links/www.chem.ualberta.ca/courses/plambeck/p101/p01017.htm
http://mathforum.org/library/drmath/view/61050.html