Q.What is Gross Error ? State the reasons for it and how to minimise the errors.

The uncertainty in any measurement is called an error, and errors fall into three fundamentally different categories.

i) Systematic errors -- reproducible, always biased in the same direction, from a problem that persists throughout the experiment:

1. Instrumental errors -- an instrument not correctly calibrated at manufacture (e.g. a metre scale with a worn-out end); fixed by careful instrument choice/calibration.
2. Imperfections in experimental technique/procedure -- limitations in the experimental arrangement itself, e.g. radiation losses from a poorly-insulated calorimeter; fixed with proper technique or applied corrections.
3. Personal errors -- caused by the individual observer: incorrect initial setup, or carelessness/lack of precaution while taking a reading.
4. Errors due to external causes -- changing external conditions (temperature, humidity, pressure) during the experiment bias the result.
5. Least count error -- set by the instrument's resolution (its smallest measurable increment, the least count); reduced only by switching to a higher-precision instrument.

ii) Random errors -- unpredictable, chance fluctuations in experimental conditions (pressure, temperature, voltage supply) or in the observer's own repeated readings (e.g. successive screw-gauge readings of a wire's thickness coming out slightly different each time). Because they are genuinely random rather than biased in one direction, they are reduced -- not eliminated -- by taking many readings and computing the arithmetic mean, taken as the best available estimate of the true value. …