Practical Skills I: Implementation & Measurements (Edexcel International A Level (IAL) Physics): Flashcards
Exam code: YPH11
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Define repeat readings.
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Define repeat readings.
Repeat readings are measurements of the same quantity taken multiple times (typically three to five times) to increase precision, reliability and confidence in the data.
How is the absolute uncertainty of a set of repeat readings calculated?
The absolute uncertainty is equal to ± half the range of the readings.
A micrometer has a resolution of 0.01 mm. To how many decimal places should its readings be recorded, and why?
To two decimal places (e.g. 1.40 mm, not 1.4 mm), because results should be recorded to the resolution of the measuring instrument.
What does calculating a mean from repeat readings do to the uncertainty in a value?
It decreases the uncertainty in the value.
Taking repeat readings and checking they are similar shows that the measurements are .........., meaning the results are not simply due to luck or a fluke.
Taking repeat readings and checking they are similar shows that the measurements are reproducible, meaning the results are not simply due to luck or a fluke.
True or False?
Taking repeat readings and calculating a mean always increases the accuracy of a measurement.
False.
Repeat readings reduce the effect of random error and increase precision, but they do not correct systematic errors, so accuracy is not guaranteed to improve.
Define a good range of measurements.
A good range covers five to ten values, with a step of 1, 2, 5 or a multiple of ten between successive readings.
Why should the interval between successive readings in a range be equal?
So the results form a clear, evenly-spaced trend; avoid uneven steps such as 1, 2, 5, 6.
Why is it important to take a wide range of readings in an experiment?
A wide range shows whether the pattern in the results holds true across all values (rather than just a narrow section), and gives an idea of how well the average represents the data.
Why should the maximum extension used when investigating a spring be limited?
To avoid exceeding the spring's elastic limit, which would permanently deform it and affect the results.
When choosing a range for a ruler, the smallest reading taken should be greater than the ruler's .........., which is typically 1 mm.
When choosing a range for a ruler, the smallest reading taken should be greater than the ruler's smallest division, which is typically 1 mm.
True or False?
Taking as wide a range of readings as possible is always the best approach in an experiment.
False.
A wider range is generally better for revealing the full pattern of results, but in practice the range achievable is limited by the time available to complete the experiment and the limitations of the apparatus.
Define significant figures.
Significant figures are the digits in a number that are reliable and absolutely necessary to indicate the quantity of that number.
Are zeros between two non-zero digits significant? Give an example.
Yes. For example, 4107 has 4 significant figures.
How many significant figures does 0.00079 have?
2 significant figures — zeros before all non-zero digits are not significant.
How many significant figures does 689.0023 have?
7 significant figures — trailing zeros within a number containing a decimal point are significant.
When rounding a number, if the digit after the last required significant figure is .......... or greater, the previous digit is rounded up.
When rounding a number, if the digit after the last required significant figure is 5 or greater, the previous digit is rounded up.
True or False?
The number 57,000 has five significant figures.
False.
Without a decimal point, zeros after non-zero digits are not significant, so 57,000 has only 2 significant figures (the 5 and the 7).
Define an anomalous result.
An anomalous result is a data point that does not fit with the trend of the other results or repeat readings, typically differing from the mean by more than 10%.
What two actions should be taken if an anomalous result occurs during an experiment?
Ignore it when calculating the mean, and repeat that measurement.
By what percentage difference from the mean is a result often considered anomalous?
More than 10%.
Why is it important to identify and remove anomalies before drawing conclusions from an experiment?
Removing anomalies makes the results more reliable, which allows more valid conclusions to be drawn.
On a graph, an anomalous result appears as a point that does not lie on the ...........
On a graph, an anomalous result appears as a point that does not lie on the line of best fit.
True or False?
An anomalous result should always be included when calculating the mean, since it is still real data.
False.
An anomalous result should be ignored when calculating the mean, since it is inconsistent with the rest of the data and would skew the average; the measurement should instead be repeated.
Define the resolution of a micrometer.
Resolution is the smallest change a measuring instrument can detect. A micrometer has a resolution of 0.01 mm.
Name the two scales found on a micrometer.
The main scale (on the sleeve/barrel) and the thimble scale (the rotating scale on the thimble).
Which part of a micrometer should be used to tighten the spindle onto an object, and why?
The ratchet, never the barrel — this reduces the risk of overtightening the object and introducing zero errors.
To how many decimal places should a micrometer reading be recorded, and why?
Two decimal places (e.g. 1.40 mm, not 1.4 mm), matching the micrometer's resolution of 0.01 mm.
A micrometer reading is taken at the point where the .......... scale aligns with the main scale.
A micrometer reading is taken at the point where the thimble scale aligns with the main scale.
True or False?
A micrometer reading of 2.3 mm is recorded to the correct number of significant figures.
False.
Micrometer readings should always be given to 3 significant figures, so this reading should be recorded as 2.30 mm, not 2.3 mm.
Define a fiducial marker.
A fiducial marker is a fixed reference point used to make more accurate timings, e.g. sighting a pendulum as it passes through its lowest point.
Why does timing multiple oscillations and dividing by the number of oscillations reduce the uncertainty in the time period?
It reduces the effect of reaction time error, since a fixed timing error is spread across many oscillations rather than affecting the timing of just one.
Why should a fiducial marker be positioned at the pendulum's lowest point rather than at the top of its swing?
The pendulum moves fastest at its lowest point, so the exact moment it passes the marker is easier to judge precisely, minimising timing error.
Why must the oscillations of a mass-spring system remain vertical throughout an experiment measuring its time period?
If the mass is pulled down at an angle, or swings sideways, this affects the time period, introducing error into the measurement.
To find the time period of one oscillation, the total time for a large number of oscillations should be measured and then .......... by that number.
To find the time period of one oscillation, the total time for a large number of oscillations should be measured and then divided by that number.
True or False?
Repeating measurements and taking a mean can correct for a systematic error in an experiment.
False.
Repeating measurements and taking a mean reduces random error; it does not correct a systematic error, which instead requires a change to the method or apparatus.
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