1.4.0 Measurements and Error

Error
Error is the difference between the actual value of a quantity and the value obtained in measurement.
There are 2 main types of error

• Systematic Error
• Random Error

Systematic Error
Systematic errors are errors which tend to shift all measurements in a systematic way so their mean value is displaced. Systematic errors can be compensated if the errors are known.

Examples of systematic errors are

1. zero error, which cause by an incorrect position of the zero point,
2. an incorrect calibration of the measuring instrument.
3. consistently improper use of equipment.

Systematic error can be reduced by

1. Conducting the experiment with care.
2. Repeating the experiment by using different instruments.

Zero error
1. A zero error arises when the measuring instrument does not start from exactly zero.
2. Zero errors are consistently present in every reading of a measurement.
3. The zero error can be positive or negative.

(NO ZERO ERROR: The pointer of the ammeter place on zero when no current flow through it.)

(NEGATIVE ZERO ERROR: The pointer of the ammeter does not place on zero but a negative value when no current flow through it.)

(POSITIVE ZERO ERROR: The pointer of the ammeter does not place on zero but a negative value when no current flow through it.)

Random errors
1. Random errors arise from unknown and unpredictable variations in condition.
2. It fluctuates from one measurement to the next.
3. Random errors are caused by factors that are beyond the control of the observers.
4. Random error can cause by

• personal errors such as human limitations of sight and touch.
• lack of sensitivity of the instrument: the instrument fail to respond to the small change.
• natural errors such as changes in temperature or wind, while the experiment is in progress.
• wrong technique of measurement.

One example of random error is the parallax error. Random error can be reduced by

• taking repeat readings
• find the average value of the reading.

Parallax error
A parallax error is an error in reading an instrument due to the eye of the observer and pointer are not in a line perpendicular to the plane of the scale.

External Link
The World of Measurement
Error Analysis (Advance Level)
Parallax Error in Meter Reading

Interactive Animation
Parallax Error - Journal of Chemical Education