The Laboratory Write-up
There are two primary functions of the lab write-up:
- To communicate the experimental work you have done and your results.
Readers may include:
- Classmates -- who may be interested in comparing their own results
to yours.
- Your teacher -- who will be interested in evaluating your performance
of the lab and your level of understanding.
- Fellow researchers -- who may want to reproduce your results for themselves.
- To keep a record for your own future use. One day you may wish
to refer back to or repeat a lab.
In order to accomplish these your write-up needs to be accurate, complete
and understandable.
As a professional experimenter (e.g. medical researcher, inventor, scientist)
your lab notebooks can be considered legal documents when, for example, you
apply for a patent. For this reason its contents must be honest and complete.
In such a notebook you will find numbered pages, so that researchers cannot
remove pages, and writing in ink.
The Style of the Write-up
In most college lab work, and in all professional lab work, the standard style
is third person, passive voice. So, one does not write, "I poured the
water from the 250 mL beaker into the erlenmeyer flask," but instead,"the
water was poured from the 250 mL beaker into the erlenmeyer flask."
This is not a very compelling way to write and it is not a very enjoyable
style of writing to read. I will normally accept your write-ups in a
more chatty first person, active voice but will occasionally ask you to try
your hand at the standard style.
The Format of the Write-up
Your write-up should almost always contain the following sections:
Header: Where you will write the lab title, the date the lab
was performed,your name and your lab partner(s)'s name(s).
Purpose: Your scientific reason for performing the lab.
Theory: The theoretical foundations of the lab. This should
include any formulas (with all variables clearly defined) used in the calculations
based on the data; and any predictions expected for the results.
Apparatus: An equipment list for the lab. This should
include manufacturer names and serial numbers where possible.
Procedure: A step-by-step guide to what you did in the lab and how
you did it. This is one of the most important sections of the write-up.
If you goofed up in performing the experiment you, or someone else, should
be able to find out how by reading this section. You need to write this section
up AS YOU ARE PERFORMING THE LAB to ensure that it is an accurate and full
representation of what you actually did. You must especially include
any steps you took that differed from those in the suggested procedure in the
lab book, or that I may have given you.
Data: The measurements that you actually took plus their reading
errors. So, if you measured the diameter of a circle in order to calculate
its area using the equation A=pr2 you
would enter the diameter measured, but not the calculated radius or area,in
the "Data" section. You will find write-ups where the data and calculations
are included in one section, but you must always remember to distinguish
between the two things.
Calculations: The calculated values based on the data.
(This should include error calculations if requested.) Include any
graphs and the results derived from them in this section. Results
are usually given in MKS units.
Conclusions: A statement of the final calculated results and
whether they agree or not with the expected values given the estimated precision
of the measurements. You should also make statements regarding
the limitations of the techniques and instruments used to perform the
lab and how you would go about improving them to increase the precision
and accuracy of the results.
Sample Write-up
Measuring the Area of the Front Cover of a Textbook, August 21, 2003,
Krusty the Klown
Lab Partner: Sideshow Bob
Purpose: to find the area of the front cover of a textbook by measuring
its length and width.
Theory: For a rectangular object the area, A, can be calculated
from the length, l, and width, w, using the formula A=l×w.
Apparatus: Tajima steel ruler, model number 1050.
Procedure: The steel ruler was placed along the long edge of
the book to ensure that length measured was at right angles to the width
dimension. The zero point of the ruler was lined up along the left
edge and the reading taken from the right edge. The width was measured
similarly.
Data: The length and width of the text were measured as: l = 25.8
± 0.05 cm
w = 20.6 ± 0.05 cm
Calculations: The area of the text is A= l×w = 531 ±2
cm2 = 0.0531 ± 0.0002 m2
Conclusions: The area of the text is 0.0531 ± 0.0002m
2. The error in the result comes from the readingerror of
the ruler and could be reduced by using a more precise instrument,
such as vernier calipers. No attempt was made to find contributions
to imprecision from other sources and the estimate of the precision could
be improved by taking multiple measurements of the dimensions
of the book to discover if the range of results indicates
imprecision from sources other than reading error.
Marking Rubric:
Labs can receive a mark up to 10. The marks are distributed according to:
Presentation: A well-presented lab using the format above with the information complete and correctly placed will receive 4 marks. One that misses a minor section (header or apparatus) or is somewhat confused or incomplete will receive 3 marks. One that misses a major section or that shows significant confusion or incompleteness will receive 2 marks. One that misses more than one major section or misses or confuses much essential information will receive 1 mark.
Data: A lab with complete and well-taken data, including reading errors, will receive 2 marks. A lab with significant omissions (such as reading errors) or poor quality data will receive 1 mark.
Calculations and discussion: A lab that has complete and correctly calculated results with error calculations, where appropriate, and intelligent discussion will receive 4 marks. A lab that is complete but with the occasional error or omission in calculations and discussions will receive 3 marks. A lab with a major omission or omissions and incoherent or significantly incomplete discussion will receive 2 marks. A lab lacking discussion and/or calculations will receive 1 mark.