There are some physical limitations in measurements, which are linked to the instrument used or to changes in the measured quantity. The variation in the value of the measured quantity, which can be small or large, is called ‘uncertainty’.
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Jetzt kostenlos anmeldenThere are some physical limitations in measurements, which are linked to the instrument used or to changes in the measured quantity. The variation in the value of the measured quantity, which can be small or large, is called ‘uncertainty’.
Some limitations in measurements are the result of the measuring instruments. The limitations of the instrument can produce results that differ from the true values. There are two sources for these errors, instrumental accuracy and instrumental functioning, as in the examples below:
Instrumental accuracy: the variation of the property you want to measure is smaller than the scale of your instrument. An example of this is when you measure the length of an object whose total length is 19.5mm, but your ruler only has centimetre marks. In this case, your measurement will only be approximate, i.e., you might get a reading of 2cm, which is a close approximation but not the true value.
Instrumental functioning: your instrument has a defect or has become inaccurate over time. An example of this is using a digital thermometer that differs from the actual temperature by 2 degrees Celsius so that all temperature readings will be off by those 2 degrees.
Every time we make a measurement or read data, we can introduce errors. The source of the error can be the instrument, the user, or the system. The errors fall into two main categories, systematic errors and random errors. There is a third type of error, known as a gaffe error, which can be a broken sensor or a wrong reading.
Systematic errors have their origin in the instruments or the system and do not happen accidentally. Systematic errors appear consistently in every measurement we take. These errors come from using an instrument in the wrong way, from a deviation within the instrument, or from the system that analyses the data. Systematic errors are always present in the system.
There are several sources of systematic errors:
Random errors are the product of chance and present when the data suddenly deviates from the measured values. They can have two sources:
Precision and accuracy are two concepts related to measurements. They determine the quality of our measured values.
Precision indicates how repeatable our measured value is. If our measuring instrument is precise, every measurement it makes will be close to every other measurement. So, measuring the weight of an object whose value is 4.3kg, we will always get a value very close to 4.3kg.
Precision does not mean the measurements are correct. An instrument can be precise but consistently deviate far from the true value. In our example of an object weighing 4.3kg, a scale might consistently produce values close to 4.0kg.
Accuracy means that the instrument delivers a value that is identical or very close to the true one. A highly accurate scale measuring the weight of a 4.3kg object will always produce values very close to 4.3kg, with only very minor variations.
To achieve measurements of high quality, we, therefore, need instruments with high accuracy and high precision.
Physical measurements are measurements of an object’s physical properties, such as its length, mass, luminous intensity, electrical charge, temperature, particle quantity, and time. Also, any combination of the seven elemental physical properties can be measured.
When measuring any property, limitations are present in the instruments or in how the user reads the measured values. Other limitations can come from the theory or the system used to measure physical properties.
What are two sources of limitations encountered in measurements?
Instruments or variations in the quantity measured.
What is a systematic error?
A consistent error in the measurement.
What is a random error?
An error produced by chance.
Can a random error be introduced by an instrument?
Yes, it can.
Can a systematic error be introduced by an instrument?
Yes, it can.
What is precision?
The ability to reproduce a measured value.
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