InLab: the lab procedure
1.
Setting up the lab:
Take
notes as you set up your experiment and calibrate instruments to help
you document your experimental protocol so that you may use it later
when writing the Methods section of your lab report.
On
a sheet of paper or in your lab manual or in a formal lab
notebook, list the lab materials you'll be using and describe the
set-up for this experiment. Take notes about potential sources
of uncertainty so that you may refer to them when you are writing
the Discussion section of your lab report. You may want to or may be
required to draw and label the instrument(s) you'll be using.
(See
below for definitions of underlined words.)
(Refer
to the web version of this document for example lab notebook pages.)
Lab
notebook:
Keeping accurate lab notebooks is very important for professional
scientists and engineers. Their lab notebooks are permanent legal records
of all work conducted in the laboratory. Because of their importance,
professional lab notebooks should be:
- Logs or journals
of all the information collected during lab, including procedures
and sketches of instruments or tools.
- Written in ink
with corrections initialed and noted.
- Labeled with
page numbers, time, date, and titles for all procedures, tables, charts,
graphs, etc.
Sources
of Uncertainty:
In science, a source of uncertainty is anything that occurs in the
laboratory that could lead to uncertainty in your results. Sources of
uncertainty can occur at any point in the lab, from setting up the lab
to analyzing data, and they can vary from lab to lab. This is why it
is so important to keep detailed notes of everything you do in the lab
procedure and any problems you encounter. Try to be especially aware
of any problems in setting up the lab, calibrating instruments, and
taking measurements as well as problems with the materials you are using.
For
advanced labs, you may want to classify the kinds of uncertainty you
have identified. Sources of uncertainty can be classified as random-those
that cannot be predicted-or as systematic-those that are related to
personal uncertainty, procedural uncertainty, or instrumental uncertainty.
2.
Preparing a table or spreadsheet for recording your data:
Using
the information you have gathered about the data you will be collecting
and list of variables from your PreLab as a guide, create a raw
data table or set up a spreadsheet for
entering data from your experiment. For help in determining
which you should create now, a table or a spreadsheet, see
below . For general information on tables, go to Designing
Tables. (refer to the web version of this document to access
these resources)
Creating
a Table or a Spreadsheet:
A table provides a very convenient tool for organizing the data you
collect in your lab. You can quickly draw a table on a sheet of paper,
you can make one with a word processing program, or you can generate
one with spreadsheet software. Using a hand-drawn table in the lab also
allows you the flexibility of entering the data into a spreadsheet at
a later time. The chief advantage to entering data in a spreadsheet
is that you can easily convert it not only into a table but also into
all sorts of graphs.
Use this guide to figure out whether or not you should use a table or
a spreadsheet for recording your data in the lab:
- If you do not
have access to a computer with spreadsheet software in your lab, then
you should create a table. You can use the data in the table to generate
a spreadsheet later, if necessary.
- If you know you
will need to create graphs for your data and have access to spreadsheet
software in the lab, then use the spreadsheet.
- If you are not
sure what form, table or graph, you will be using to report your findings
and it is convenient to use a spreadsheet, then use a spreadsheet.
- If creating a
spreadsheet in the lab will take too much lab time, then use a table
and create the spreadsheet later.
3.
Conducting the experiment:
Conduct your experiment
as set up in the PreLab and record your data in a table or spreadsheet
(see question 2 above). Take detailed notes on your experimental procedures.
These notes may be all you have later on when you write your lab report.
It's also important to note any problems you have with the experiment;
these notes could be useful when writing the Discussion. Describe in
writing or sketch out on a sheet of paper your observations as you collect
data during the experiment (observations are potentially significant
things that are not reflected in the measurements: color, smell, interesting
reactions, unexpected behaviors, etc.)
As you record your
data, take note of any trends emerging in the data. You should be asking
yourself various questions: What are the relationships
among the variables? Do the data behave in the way that you had
anticipated? If not, why not? You may need to consider sources
of uncertainty once again. Sources of uncertainty may affect the
accuracy
and precision of your experimental data. (See below for definitions
of underlined words.)
Note: If
the results of your experiment do not seem to lead you to an answer
to your research question, you may need to rethink the design of your
experiment, which could mean revising the experiment, revising the variables,
revising the hypothesis, or even revising the research question. A good
scientist must be flexible in designing and conducting experiments.
Remember that the most important part of an experiment is that it is
clearly designed so that it may be repeated by others seeking to reach
the same conclusions. Whether you are right or wrong with respect to
your hypothesis is not as important as a well-designed experiment.
Relationships
Among the Variables:
Since dependent variables "depend" on independent variables,
there has to be a relationship between the two. The relationships between
the dependent and independent variables are what is described in the
hypothesis. So it's important to determine what those relationships
are in order to see whether or not the hypothesis has been supported.
Sources
of Uncertainty:
In science, a source of uncertainty is anything that occurs in the
laboratory that could lead to uncertainty in your results. Sources of
uncertainty can occur at any point in the lab, from setting up the lab
to analyzing data, and they can vary from lab to lab. This is why it
is so important to keep detailed notes of everything you do in the lab
procedure and any problems you encounter. Try to be especially aware
of any problems in setting up the lab, calibrating instruments, and
taking measurements as well as problems with the materials you are using.
For
advanced labs, you may want to classify the kinds of uncertainty you
have identified. Sources of uncertainty can be classified as random-those
that cannot be predicted-or as systematic-those that are related to
personal uncertainty, procedural uncertainty, or instrumental uncertainty.
Accuracy and Precision:
Accuracy refers to the closeness of a measured value to a standard or
known value. For example, if in lab you obtain a weight measurement
of 3.2 kg for a given substance, but the actual or known weight is 10
kg, then your measurement is not accurate. In this case, your measurement
is not close to the known value.
Precision
refers to the closeness of two or more measurements to each other. Using
the example above, if you weigh a given substance five times, and get
3.2 kg each time, then your measurement is very precise. Precision is
independent of accuracy. You can be very precise but inaccurate, as
described above. You can also be accurate but imprecise.
For
example, if on average, your measurements for a given substance are
close to the known value, but the measurements are far from each other,
then you have accuracy without precision.
A
good analogy for understanding accuracy and precision is to imagine
a basketball player shooting baskets. If the player shoots with accuracy,
his aim will always take the ball close to or into the basket. If the
player shoots with precision, his aim will always take the ball to the
same location which may or may not be close to the basket. A good player
will be both accurate and precise by shooting the ball the same way
each time and each time making it in the basket.
4.
Visualizing the data:
Now that you have
entered your data in a table or spreadsheet, you are ready to represent
the data in the appropriate visual format for your lab report. Representing
your data in a visual format will allow you to identify trends and relationships
among variables more easily. Follow these steps:
- Establish what
types of data you have, quantitative or qualitative
(refer to the Resources page in the web version of this document;
once there, choose "Data Types").
- Determine if
the data should be represented as a table or a graph
(refer to the Resources page in the web version of this document;
once there, choose "Tables vs. Graphs").
- If you decide
to use a graph to represent your data, determine which type
of graph is one that best represents your data (refer to
the Resources page in the web version of this document; once there,
choose "Graph Types").
- If a table is
the best format for your data, then modify the table you used to collect
your data so that it is labeled and organized properly (refer to the
Resources page in the web version of this document; once there, choose
"Designing Tables").
- If you need help
creating a spreadsheet to make a table or graph, refer to the Resources
page in the web version of this document. Once there, choose "Excel
Tutorial".
- Remember that
the purpose of your table or graph is to summarize your findings for
yourself and for others and to reveal trends in your data.
5.
Using your data to solve your research problem:
Review all your
data--tables, graphs, and drawings--to establish whether or not or to
what degree the data support your hypothesis. Next, use what you have
learned from comparing data to the hypothesis to answer your research
question. State the answer as best you can in a sentence or two. Then
return to the original problem you were given to solve, both the knowns
and the unknowns that you defined in Question 1 of the PreLab. Does
the answer to your research question resolve the unknowns and allow
you to solve the problem? If so, write the solution. If your answer
still does not provide a satisfactory resolution to your research question
and the original problem, you may need to explore alternatives: a different
experiment, a different hypothesis, a different research question.
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