Scientific and Technical Lab Reports

Careful documentation during the experiment or study is essential to accuracy in reporting. Writing style must be clear, concise, and objective. Standard usages and grammatical accuracy are expected.

Unless otherwise specified, final papers should be neatly typed (double-spaced with one-inch margins) on standard-sized white paper.

Reports should be organized according to the following structure and should include all of the subheadings except for the title page.

Title Page A descriptive title must clearly identify the topic, the nature of the research, for example, An Analysis of the Mineral Composition of the Water in Greasy Lake. The writer's name and other relevant information such as the course, the teacher, and the date the report is due follow. These items are centered line by line and the page has even margins top and bottom.

Abstract A separate page for the abstract presents a short summary of the significant points of the paper, usually 250 or fewer words.

Introduction In a paragraph or two, the introduction states the problem and the purpose of the report, including a clear statement of the hypothesis. This section identifies the outcome as well as necessary background information readers need to understand the context. It includes definitions of terms that readers need to know. If the teacher or editor requires a review of existing literature on the topic, that information belongs in the introduction. Here, as elsewhere in the paper, documentation of sources does not use footnotes but does use parenthetical in-text citations with the name-year method, for example (Wiggins, 1984). Paragraph rather than list structure is used for this section of the paper.

Materials and Methods Precise, detailed information about the experiment or study includes exactly what was done, using exact measurements rather than approximate measurements. Diagrams and tables may accompany this section but cannot substitute for clear explanations. Methods used to verify the authenticity of data should be included.

Materials should be incorporated within the narrative rather than in a list. The narrative should be written in past tense rather than as instructions in the imperative present (for example, I filled six petri dishes with agar or Six petri dishes were filled with agar not Fill six petri dishes with agar).

From the details in this section, readers should be able to duplicate the experiment.

Results This data section contains little explanatory information and no judgments or conclusions. Instead, it presents tables, graphs, and diagrams with brief explanations. Each table must have a heading and must be numbered consecutively.

Discussion This section explains what happened in the experiment and how the researcher derived the conclusions. If the data refute the original hypothesis, explanations are appropriate. The meanings and significance of the findings appear here.

Literature Cited This bibliographical section begins on a separate page from the text. An alphabetical list by author's last name includes all publications and studies mentioned in the report, following one of the accepted style guides for the field of research, for example, American Psychological Association style (APA) or Council of Biology Editors style (CBE).

EXAMPLE: Baldwin, K. M. 1979. Cardiac gap junction configuration after an uncoupling treatment as a function of time. J. Cell. Biol. 82: 66-75. Berlyn, G. P., and J. P. Mishke. 1976. Botanical microtechnique and cytochemistry. Iowa State Univ. Press, Ames.

Options Some writers present a separate section of conclusions; however, conclusions often appear in the discussion section. An acknowledgments page after the abstract is appropriate if other people assisted with the research, the experiment, or the preparation of the report.

Sample Report

I. PURPOSE

The purpose of this lab is to investigate the characteristics of series AC circuits.

II. THEORY:

The behavior of series AC circuits is similar to those of DC series circuits. The basic laws such as Ohm's Law, Kirchhoff's Current and Voltage Laws, Current and Voltage Divider Rules, and the additive properties of resistance and power hold true. The differences lie mainly in the methods of analysis used for AC circuits which are somewhat more complicated than those used for DC analysis.

The circuit consisting of a resistor, a capacitor, and an inductor in series was placed in series with a frequency generator. Voltages were measured, recorded and compared with calculated values. Since resistances in series can be rearranged in any given order, it was possible to measure each value with respect to ground, which is sometimes necessary when using an oscilloscope.

Although the term "resistance" was used in the above discussion, the actual term is really impedance. The impedance of the resistor at most frequencies (below a few hundred kilohertz) is equal to its resistance value. In a purely resistive circuit, resistance is unaffected by a sinusoidal voltage. Therefore, the current through and the voltage across the resistor will be in phase. The use of vectors known as phasor algebra most easily expresses this type of relationship. This mathematical "tool" expresses the magnitudes of currents, voltages, and impedances along with the value of the phase angle in degrees. Using this tool, one can create an impedance diagram by plotting resistance on the positive horizontal (real) axis, and reactance on the vertical (imaginary) axis.

In an ideal inductor, the voltage is said to lead the source current by 90 degrees. The inductive reactance is, therefore, plotted on the positive imaginary axis which is denoted as "j". In an ideal capacitor, the voltage lags the source current by 90 degrees. The phase angle, therefore, is 90 degrees and the capacitive reactance is plotted on the negative imaginary axis which is denoted as "- j". These values can be expressed in two formats. In rectangular form, the value is composed of the real value along with the imaginary value. This is known as a complex number with the format: C = A + jB. The other form is polar form, which expresses the resultant magnitude and the phase angle with the format: C = C .

The effects of frequency on reactance are also to be considered. Since inductive reactance is equal to the product of (2 )(f)(L), reactance increases with frequency. Capacitive reactance equals 1/(2 *)(f)(c), which means that as frequency increases, reactance decreases. Analysis for a given circuit is, therefore, limited to a specific frequency. Because the components are not ideal, phase relationships may vary from the ideal 90 degrees. A voltage diagram of measured voltages should, however, indicate a strong similarity to the calculated voltages.

PROCEDURE:

1. Measure all components on the impedance bride. (Also measure the inductor's resistance.) 2. Using the oscilloscope and a small series resistor, calculate the effective resistance and inductance of the inductor. 3. Construct a series circuit with the components and a frequency generator. 4. Measure voltage across each element with respect to ground. (rearranging as necessary) 5. Design an equivalent circuit. (two element) 6. Draw a phasor diagram with measured and predicted results on the same axes but with different colors. 7. Repeat steps 1 through 5 at 4K.

RESULTS: (See print copy available at the Writing Center)

CONCLUSIONS:

This lab definitely proved to be a challenge both in making the measurements and performing the calculations. Though applications of the basic laws of DC circuits were used, the mathematics necessary for AC analysis was more demanding. It was hard to be accurate beyond two significant figures when making measurements with the oscilloscope. Certainly, this lack of precision was part of the reason for inaccuracies. Another possible cause for error is the inductor. The resistance (67.5 ohms) had to be accounted for when calculating total impedance and when calculating the voltage across the inductor itself. But more important may be the effect of power losses due to hysteresis, eddy currents, skin effect, and radiation. Since radiation losses only occur at radio frequencies, these can be ruled out at 2khz, but the bottom line is that any loss of power translates into a gain of effective resistance. If the total power is divided by the square of the total current, the result is the effective resistance. (by rearranging P = I2R) The calculated result for the lab circuit was 395 ohms which matches the resistance of the equivalent circuit. The measured value is 413 ohms which makes a difference of 18 ohms in the effective resistance.