Write type of error in measurement of physical quantity and explain.

Error caused in observation of physical quantities are categorized as follows :

$(a)$ Systematic Error

$(b)$ Random Error

$(a)$ Systematic Error :

Error caused when measured value is different than true value is called systematic error. These error are in one direction either positive or negative. Some sources of systematic error are as follow :

$(i)$ Instrumental Error:

* These error arise due to imperfect design or calibration of the measuring instrument, zero error in instrument.

Example : If temperature graduation of a thermometer may be inadequately calibrated then at $STP$ temperature of boiling water will read $104^{\circ} \mathrm{C}$ instead of $100^{\circ} \mathrm{C}$.

In a vernier calipers the zero mark of vernier scale may not coincide with zero mark of main scale.

In ordinary meter scale, one end is worn off.

$(ii)$ Imperfection in Experimental Technique or Procedure :

If thermometer used to measure body temperature is not properly placed in contact of body it will not give actual value of body temperature.

External condition such as changes in temperature, humidity, wind velocity during experiment

may systematically affect the temperature.

$(iii)$ Personal Error:

Personal error arise due to an individual bias, lack of proper setting of the apparatus or individual's carelessness in taking observations without observing proper precaution.

For example : If you by habit always hold your head a bit too far to the right while reading the position of a needle on the scale, error can introduced due to parallax.

Systematic errors can be minimized by improving experimental technique selecting better instruments and removing personal bias as far as possible.

$(b)$ Random Error:

Error which occur irregularly and random with respect to sign and size are called random error.

These error arise due to random and unpredictable fluctuation in experimental condition.

For example : When same person repeats the same observation it is likely that he may got different readings everytime.

- These error may by positive or negative.