2013-12-08

Experimental Errors

When doing experiments there are several errors that we need to consider. For example the error when taking reading from instruments and also the influence from the outer surroundings. This is true for all scientific investigations. Even machines have errors! and they do need to be calibrated consistently!

Error is the difference between the measured value and the real or actual value. (The difference in reading is known as the error)

Two main types of error are systematic error and random error.

Systematic error occurs when there is an error when reading the scale that is being used. It is caused by the surroundings, the instrument itself (scale may not be uniform or even blurred due to wear and tear) and of course the observer error.

Systematic error results in the measurement or reading being consistently over the actual value OR consistently smaller than the actual value.

There are several possible causes of systematic error:

One of the most common error is the Zero Error. Zero Error is caused if the reading shown is Not zero when the true value is actually zero. This is most probably caused by a flaw in the instrument for example when using a ruler that has lost its zero scale due to wear and tear hence causing an error in the measurement of length.

Wrong assumptions may also cause error, for example if you assume that water boils at 100 degree celcius but actually its boiling point is higher if there are impurities in it. (Pure water boils at 100 degree celcius)

There is also a possibility to create error when there is a lag of reaction time. For example in a sports day, when measuring a 100 m running time using a stopwatch. The observer may not press the stop button exactly when the foot of the runner touches the finishing line.

Sometimes, as I have mentioned, instruments that are not properly calibrated could also cause error and this has to be put in consideration when writing a report or when there is an anomaly in reading.

Another type of error that needs to be considered is Random Error.

Random error is caused by the observer who reads the measuring instrument. Just like the systematic error, there can exist positive or negative error. Positive error is when the reading is bigger than the real value and negative error is when the reading is smaller than the real value.

One of the ways to reduce random error is to take several readings for a measurement and then taking the average reading to be analysed.

There are several examples of random error.

Miscounting numbers during observation or change in the surrounding due to temperature, wind, light, exposure to chemicals or impurities may cause error. Sometimes the observer may read the scale wrongly (as in the case of reading a scale in on a beaker or ruler (parallax error). Parallax error occurs when a reading is taken from an unsuitable position relative to the scale.

Ways to reduce error

Magnifying glass to enhance the visual of scale on the instrument.
Avoiding parallax error by positioning the instrument (meter rule) properly on the table with the eyes perpendicular to the scale. This also applies when reading other instruments. Parallax error can also be reduced by putting a strip of mirror next to the scale (for example in ammeter), the eye must be positioned so that the image formed on the mirror is fully covered by the indicator hand of the ammeter.

Some instruments can be adjusted to eliminate zero error. For example when using an ammeter, there is an adjuster to set the indicator to zero before making any measurement.

In the case of a ruler, measurement can be carried out starting from the next clear scale for example if scale 0.0cm is blurred, we can start measuring the length from 2.0cm, of course taking the difference of value in consideration when recording the final reading.



2 comments:

Andy Yeo said...

May I trouble you to write on these topics:

Vectors and Force
Material Strength - stress and strain
Static Equilibrium

Thanks a million

Anonymous said...

Thank you soo much! Truly appreciated.