Demonstrate good analysis skills, applying logic and reasoning.But when you say “several sources of error,” it makes the experiment seem far worse than it probably was.) Avoid sounding dramatic, like “the experiment was a disaster” or “there were several sources of error.” (There might indeed be several sources of error, but usually only 1-2 are dominant and the others are relatively minor. On the other hand, if you get 20.43 g on one scale, but 20.45 g on another scale, this error is probably insignificant-not worth describing (since the percent error is below 0.1%). If instead you say that you measured the mass to be 21.4 g on one scale, but 20.8 g on another scale, you’ve established that there is a problem with the scales (but note that this is a 3% error: if your percent error is much larger than 3%, there is a more significant source of error involved). For example, saying that a scale might not be calibrated properly sounds hypothetical. It’s better if it sounds like your source of error is based on observations that you made during lab. For example, if you measure gravitational acceleration in a free fall experiment to be larger than 9.81 m/s 2, it would be inconsistent to cite air resistance as a source of error (because air resistance would cause the measured acceleration to be less than 9.81 m/s 2, not larger). The error should be consistent with your results.In addition to identifying the source of the error, you can describe how it impacts the results, or you might suggest how the experiment might be improved (but only suggest improvement sparingly-not every time you describe a source of error), for example. Unless otherwise stated by the lab manual or your instructor, you should describe the source of error in detail.You should describe the source of error as precisely as possible.For example, when a car rolls down an inclined plane, its mass cancels out in the equation for acceleration (a = g sin θ), so it would be incorrect to cite an improperly calibrated scale as a source of error. It needs to actually affect the results.It should be significant compared to other sources of error.It should sound like an inherent problem that you couldn’t plausibly avoid.When you identify and describe a source of error, keep the following points in mind: Don’t blame your lab partner-at least, not in your report-because it isn’t a valid source of error. Simply redo the experiment, taking care to release the masses so that they don’t collide. For example, if you perform the Atwood’s machine lab and the two masses collide, it’s a mistake to keep the data. If an accident occurred during the experiment, which could plausibly be avoided by repeating the experiment, this is not a source of error. Sure, some students make mistakes, but mistakes are not sources of error. Calculation mistakes are something that students are expected to avoid. If there are mistakes in your calculations, these are not sources of error. A source of error is something that you could not plausibly expect to avoid. If you used equipment incorrectly or followed the procedures incorrectly, for example, these are mistakes-they are not sources of error. You can definitely find more significant sources of error to describe instead of round-off error. ![]() Even a cheap calculator provides at least 8 figures, whereas most first-year physics experiments yield results where only 2-3 of those digits are significant figures. This problem with this is that students almost never have enough precision in their answers for round-off error to be significant. Advice: Don’t write the phrase “human error” anywhere on your lab report. It may be okay if the nature of the error is human in origin (provided that it’s an inherent error and not a mistake), but it’s not okay to be express the error in vague terms. The problem with this phrase is that it’s way too vague. ![]() Part of learning how to write a good sources of error section includes learning what not to do.įollowing are some common incorrect answers that students tend to include in their sources of error section. We will see examples of each in the remainder of this article.
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