General Information
Your labs will require you do several different things: simulate your
circuit, construct your circuit, characterize (measure voltages and
currents)
your circuit, and compare your experimental results with the results
from the simulation.
Your lab report has to show that you did all these things and it should
demonstrate that you understood the concepts behind the circuits and
the data.
- The most important part: You should already have a
good idea what results you should get.
- Setting up experimental circuits requires attention
to detail. A single wrong connection can still give you results. But
they are virtually always different from the ones you should have
observed. If you don't know what to expect, you don't know when it is
wrong.
- Electronic components fail.
- A burned out fuse of a voltage supply line is
only easy to find when you search for it. But when you don't know that
your results are wrong, you will not look for it.
- A broken transistor or burned out diode is not
going to tell you that it is broken. If you don't know what to expect,
you will not know that.
- If you just follow the instructions, take data, and
then try to make sense of all this later when you write your lab
report, you will be surprised at how much can go wrong.
- How do you know what to expect?
- Understand the circuits before you come to class.
- Estimate what to expect often.
- Use the data sheets.
- During the experiments:
- Measure voltages not only at the outputs but also
at other locations in the circuit. Do these values make sense? Put them
in your lab book.
- It is often useful to modify the circuit a bit to
check if the result changes as expected. For example: A transistor is
often used to amplify a current. But this can only work if the
collector is powered. Disconnect the power from the collector. If
nothing changes, your transistor is probably broken. or hooked up
incorrectly.
The
Parts of a Lab Report
You should organize your information into several
categories:
- The Title identifies the topic of your report:
- Lab 1: Simple sensors / DC etc.
- You are the Author and your lab partner is
listed as "partner."
- Author: John Doe, Partner: Jane Doe
- In case you did parts of the lab alone or with a
different partner because your original partner missed parts of the
class, mention here which parts you did alone or with a different
partner.
- Subheading, indicating what is being done.
Generally, each lab consists of a series of small sub-experiments. For
example, in Lab. 2 you study a phototransistor, a temperature sensor,
the oscilloscope, the function generator, a high-pass filter, a
low-pass filter, and finally a microphone with a coupling circuit.
Cover each of these sub-experiments completely as described in
the following sub-bullets before describing the next sub-experiment.
- Paragraph about the motivation for this
sub-experiment: What is the goal? What am I expected to learn? It
is important in physics to not loose sight of the goal among all the
details.
- Circuit diagram: This can be a copy of the
circuit built in the simulator.
- It should include names for all components and
nodes in your circuit.
- Add a list of components used. Maybe in form
of a table. Use the real values wherever possible (as measured
resistances or capacitances).
- Measured Voltages from DC power supplies
should be listed as well.
- Experimental Procedure describes the process
in a short clear paragraph, explaining all steps in the order they
actually happened, not as they were supposed to happen. Refer to the
circuit diagram to support your explanations. The procedure should not
include the measurement of the resistors, capacitors, and supply
voltages listed above (we just assume you did this correctly). Do not
copy text from the lab manual to the report, but do describe what you
did. Be sure you describe those occasions when you did not follow the
manual exactly (e.g., "At step 4 we performed four repetitions instead
of three, and ignored the data from the second repetition"). If you've
done it right, another researcher should be able to duplicate your
experiment.
- Results include results from the simulation
and from your experiment. Results can be given in the form of data in a
table or as a graph.
- Graphics need to be clear, easily read, and well
labeled (e.g., "Figure 1: Output voltage as a function of signal
frequency"). An important strategy for making your results effective is
to draw the reader's attention to them with a sentence or two within
the normal text, so the reader has a focus when reading the graph. One
very common mistake are the 'screenshots' from the scope. They are
often not labelled correctly and neither you nor I want to guess later
which scale is the correct one.
- Compare your results with your expectations.
Graphs should include the data as data points and a curve based on the
expected result should be fitted to the data if possible.
- Follow with a brief discussion how the circuit
works. Show that you understand the experiment. Do you think that the
differences between experiment and theory are acceptable? Are they
consistent with uncertainties in the measurements, within range of data
sheets? Any other excuses why the results might be off?
- Summary/General discussion:
- Summarize what you observed and what was learned
when you look at the entire set of experiments. What is the point of
this set of experiments?
- Put the sub-experiments/results in a larger
context. This could be some fundamental physics background: For example
one of Kirchhoff's laws is a consequence of charge conservation. Or the
larger context could be potential applications. But keep it short.
There are no bonus points for long novels.
- Lab Report Guidelines
- Label all figures and tables with a descriptive
sentence.
- e.g., "Figure 1: Output from a high-pass filter,
using as input a 60 Hz, 2 V, square wave. R = 10k, C =
100 pF."
- When you compare your observed value with your
calculated value, do the comparison as a percent difference.
- Percent deviation (difference): ( ( |measured -
expected| / expected) * 100 )
- e.g., "We calculated the driving current of the
current mirror to be 1.0 mA. The measured output is 1.6 mA. This is a
60% deviation from the theoretical expectation."
- Show the complete analysis of your work. "Yes." is
never accepted as an answer.
- Example: the lab asks you if the output from a
circuit is what you expect. "yes" is not appropriate. What is more
appropriate is: "We expect that the half-wave circuit will only pass
the positive swing of the input AC current. We displayed the input AC
wave on the scope, along with the output of the circuit. We observed
the positive swing at the output of our circuit, and a flat line at 0
during the time when the input is swinging negative. Our output matches
our expectation."
- Show all data to support your statements.
- Example: you are asked to vary frequency of the
input AC wave and check that the time constant of your circuit does not
change. Stating that "we varied the frequency and found tau didn't
change" is not good. What's your proof? Why should I trust you? More
importantly, how do I know you didn't copy the work from someone else?
You have tables of results in your lab notebook. Turn those tables into
plots for your report. You can also take scope images. All of these
things should be used to defend your conclusions.
- Answer all questions for each part of the lab.
Please ask if you aren't sure if something should be answered. Put the
questions and the answers in the part of the report where they are
relevant.
- Lab partners results must be consistent. You should
have the same images and the same data points (2.90 and 2.88 are fine.
2.02 and 2.19 are not). If there are any problems sharing information
please let me know.
- If you miss a day, you may not copy data taken by
your lab partner while you were absent. You will need to repeat these
measurements yourself at a time when your partner does not need the
equipment.
- You must have correct spelling, proper grammar, and
use correct scientific terms to describe effects.