General Information

A good lab report does more than present data; it demonstrates your comprehension of the concepts behind the data. Merely recording the observed results is not sufficient; you should also identify how and why differences from expectation occurred, explain how they affected your experiment, and show your understanding of the principles the experiment was designed to examine. You still need to organize your ideas carefully and express them suscintly.

Do not repeat trivia such as the purpose of the experiment, which can be found in the lab manual. Avoid verbiage and generalities. Be concise, but not so brief as to be vague.

The Parts of a Lab Report

• The Title identifies the topic of your report.


• You are the Author and your lab partner is listed as "partner."


• Subheading, indicating what is being done. Generally, each lab consists of a series of small 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 experiments completely as described below before describing the next experiment.


• Methods and Materials (or Equipment) can usually be a simple list, but make sure it is accurate and complete.


• 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. 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.


• Show circuit diagrams or block diagrams for each step. Label all the components and the inputs and outputs of the circuit.


• Results are usually given in calculations and figures; however, you still need to state all significant results explicitly in verbal form, for example: "Using the calculated I gives R = 0.1244 +/- 0.0003 Ohms." Be sure to use the appropriate precision. Do not duplicate data in figures with tables. The table should be in your lab notebook.

Graphics need to be clear, easily read, and well labeled (e.g., "Figure 1: Input Frequency and Capacitor Value"). An important strategy for making your results effective is to draw the reader's attention to them with a sentence or two, so the reader has a focus when reading the graph



• Discussion is the most important part of your report, because here, you show that you understand the experiment beyond the simple level of completing it. Explain. Analyse. Interpret. Some people like to think of this as the "subjective" part of the report. By that, they mean this is what is not readily observable. This part of the lab focuses on a question of understanding "What is the significance or meaning of the results?" To answer this question, use both aspects of discussion:


• 1. Analysis What do the results indicate clearly? What have you found? Explain what you know with certainty based on your results and draw conclusions:

"Because none of the samples reacted to the Silver foil test, therefore sulfide, if present at all, does not exceed a concentration of approximately 0.025 g/l. It is therefore unlikely that the water main pipe break was the result of sulfide-induced corrosion."



• 2. Interpretation What is the significance of the results? What ambiguities exist? What questions might I raise? Find logical explanations for problems in the data:

"Although the water samples were received on 14 August 2000, testing could not be started until 10 September 2000. It is normally desirably to test as quickly as possible after sampling in order to avoid potential sample contamination. The effect of the delay is unknown."

More particularly, focus your discussion with strategies like these:

• Compare expected results with those obtained.
• If there were differences, how can you account for them? Saying "human error" implies you're incompetent. Be specific; for example, the instruments could not measure precisely, or calculated values did not take account of other effects. Analyze experimental error and propagate it to the final result.
• Was it avoidable? Was it a result of equipment? If an experiment was within the tolerances, you can still account for the difference from the ideal. If the flaws result from the experimental design explain how the design might be improved. Explain your results in terms of theoretical issues.
• Often undergraduate labs are intended to illustrate important physical laws, such as Kirchhoff's voltage law. Usually you will have discussed these in the introduction. In this section move back from the results to the theory. How well has the theory been illustrated? Relate results to your experimental objectives.


• Now repeat, with a new subheading, for the next small experiment.

Lab Report Guidelines

• You will not be penalized if you don't produce the expected result from a lab. You will lose points if you do not try to explain why your observation differs from expectation.
• 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. Make 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.