Write short notes on the following:
a. Unit
b. Rounding -off
c. Dimensionless quantities

Explanation

a. Unit: An arbitrarily chosen standard of measurement of a quantity, which is accepted internationally is called unit of the quantity.
The units in which the fundamental quantities are measured are called fundamental or base units and the units of measurement of all other physical quantities, which can be obtained by a suitable multplication or division or powers of fundamental units are cakked derived units.
b. Roundign-off: The result given by a calculator has too many figures. In no case should the result have more significant figures than the figures involved in the data used for calculation. The result of calculation with numbers containing more than one uncertain digit should be rounded off.
c. Dimensionless quantities:
(i) Physical quantities which have no dimensions, but have variable values are called dimensionless variables. Example are gravitational constant, Planck's constant etc.
(ii) Quantities which have constant values and also have no dimensions are called dimensionless constants. Examples are `pi,e,` numbers etc.