|Rules for Emailing of Lab Reports and Assignments
- 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.
- Name your file by "YourName-subject-assignment.xls". (For example: JohnSmith-MEM23061A-hounsfield.xls, or JSmith-testing-ass3.xls, etc )
- Your email must have your name in the subject.
- If multiple assignments to be submitted, attach them all in a single email.
- 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
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.
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
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
measurements are added or subtracted, the absolute
error is added.
When measurements are multiplied or divided, the relative error is
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.
for information about scientific errors