What are the types of errors are there with measuring instruments?
Ans: There are seven types of errors
1. Constant errors
2. Systematic errors
3. Environmental errors (Errors due to external causes)
4. Personal Errors or Observational Errors
5. Random Errors
6. Gross errors
Constant errors:
When results of series of measurements are in error by the same amount, such error is called constant error.
The constant errors are due to imperfect design zero error in the instrument or any other such defects. These are also called ‘instrumental errors’.
These errors are called constant error because, with the given instrument the error will be of the same magnitude and same sign(either always positive or negative). These errors can be determined beforehand and the measurements can be corrected for.
Systematic errors:
Systematic errors are those errors that tend to be always in one direction. These errors will be always either positive or always be negative. Systematic errors with constant magnitude are called constant errors.
Other types of systematic errors:
1. Environmental errors (Errors due to external causes)
These errors are due to external conditions, that is, due to change in environment. During the experimental measurement there may be changes in external conditions-changes in temperature, pressure, humidity, wind velocity etc.
These errors systematically affect the measurements.
For example, due to rise in temperature a scale gets expanded and this results in error in measuring the length.
2. Imperfection in experimental technique or procedure
Even the cause of error is quite well known, sometimes error cannot be eliminated due to imperfection in experimental arrangement, procedure followed and technique employed.
For example, in calorimeter experiments, the loss of heat due to radiation, the effect on weighing due to buoyancy of air cannot be avoided.
A thermometer placed under the armpit will always show a temperature lower than the actual value of body temperature.
These errors will be always present and can be suitably corrected for.
3. Personal errors or observational errors
These errors are entirely due to personal peculiarities of the experimenter.
Causes:
Individual bias, lack of proper setting of the apparatus, carelessness in taking observations etc. are the causes for this type of errors.
A person may be habituated to hold his eyes always a bit too far to the right (or left) while taking the readings with the scale. We know that this will give rise to parallax error.
The more experienced and the more cautious and attentive the observer becomes, the less will be the personal errors.
The effect of observational errors can be minimized by obtaining several readings with due care and then taking the arithmetic mean of the readings. The systematic errors can be minimized by
· Selecting better instrument with higher resolution.
· Taking care to avoid personal bias as far as possible.
· Improving the experimental techniques.
Random Errors:
Unlike systematic errors these errors are at random with respect to the sign and magnitude. They occur irregularly - sometimes increasing sometimes decreasing with changing magnitudes. These errors arise due to fluctuations in experimental conditions that cannot be predicted.
Examples:
Random fluctuations in temperature, voltage supply and mechanical vibrations of experimental set up etc. are the causes for random errors.
Gross errors:
While noting down the length of an object, the experimenter may read a value of 4.21 cm but may record it as 2.41 cm or 1.24 m. This is improper recording. This results in gross error.
Causes:
· Neglect of the sources of error
· Reading the instrument incorrectly
These gross errors are the result of sheer carelessness on the part of the observer. No corrections can be applied to these errors. Care should be taken to avoid such errors. Taking all precautions that are required, we can minimize gross errors. Actually these gross errors are to be called as mistakes and are to be avoided.
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