Measurements.

A.The measured physical quantity consists of two parts.

a. The numerical value

b. The unit

Example : If a person reports that the volume of the liquid in a burette is 36.5 ml. In this 36.5 represents the numerical value and ml(which stands for milliliter) represents the unit.

B. Every scientific measurement has some degree of uncertainty. This is mainly due to skill of the observer and limitation of the instrument.

C.If a centimeter scale is used to measure the length of a page, we might find that it is 13.7 centimetre. In this case we would be sure that the number of tens in the numerical expression is 1 and the number of one is 3. However we can’t be sure of the number corresponding to tenths of a centimeter.

D. One of the method of expressing uncertainty is to use the notation$\pm 1$along with the doubtful, digit. Hence the uncertainly in length, can be expressed the uncertainly in measurement as$13.7\text{\&}\pm 0.1$ cm

E Another convenient method of expressing the uncertainly in measurement is to express it in terms of significant figures instead of using the notation $\pm 1$