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Current Affairs 11th Class

Fundamental and Derived Quantities

(1) Fundamental quantities : Out of large number of physical quantities which exist in nature, there are only few quantities which are independent of all other quantities and do not require the help of any other physical quantity for their definition, therefore these are called absolute quantities. These quantities are also called fundamental or basic quantities, as all other quantities are based upon and can be expressed in terms of these quantities. (2) Derived quantities : All other physical quantities can be derived by suitable multiplication or division of different powers of fundamental quantities. These are therefore called derived quantities. If length is defined as a fundamental quantity then area and volume are derived from length and are expressed in term of length with power 2 and 3 over the term of length. Note : q In mechanics, Length, Mass and Time are arbitrarily chosen as fundamental quantities. However this set of fundamental quantities is not a unique choice. In fact any three quantities in mechanics can be termed as fundamental as all other quantities in mechanics can be expressed in terms of these. e.g. if speed and time are taken as fundamental quantities, length will become a derived quantity because then length will be expressed as  Speed ´ Time. and if force and acceleration are taken as fundamental quantities, then mass will be defined as Force / acceleration and will be termed as a derived quantity.  
Catgeory: 11th Class

Fundamental and Derived Units

Normally each physical quantity requires a unit or standard for its specification so it appears that there must be as many units as there are physical quantities. However, it is not so. It has been found that if in mechanics we choose arbitrarily units of any three physical quantities we can express the units of all other physical quantities in mechanics in terms of these. Arbitrarily the physical quantities mass, length and time are chosen for this purpose. So any unit of mass, length and time in mechanics is called a fundamental, absolute or base unit. Other units which can be expressed in terms of fundamental units, are called derived units. For example light year or km is a fundamental unit as it is a unit of length while s-1, m2 or kg/m are derived units as these are derived from units of time, mass and length. System of units : A complete set of units, both fundamental and derived for all kinds of physical quantities is called system of units. The common systems are given below (1) CGS system : This system is also called Gaussian system of units. In this length, mass and time have been chosen as the fundamental quantities and corresponding fundamental units are centimetre (cm), gram (g) and second (s) respectively. (2) MKS system : This system is also called Giorgi system. In this system also length, mass and time have been taken as fundamental quantities, and the corresponding fundamental units are metre, kilogram and second. (3) FPS system : In this system foot, pound and second are used respectively for measurements of length, mass and time. In this system force is a derived quantity with unit poundal. (4) S. I. system : It is known as International system of units, and is extended system of units applied to whole physics. There are seven fundamental quantities in this system. These quantities and their units are given in the following table Unit and symbol of quantities  
Quantity Unit Symbol
Length metre m
Mass more...
Catgeory: 11th Class

S.I. Prefixes

In physics we deal from very small (micro) to very large (macro) magnitudes, as one side we talk about the atom while on the other side of universe, e.g., the mass of an electron is 9.1 x 10-31 kg while that of the sun is 2 x 1030 kg. To express such large or small magnitudes we use the following prefixes :     Prefixes and symbol
Power of 10 Prefix Symbol
1018 exa E
1015 peta P
1012 tera T
109 giga G
106 mega M
103 more...
Catgeory: 11th Class

Standards of Length, Mass and Time

(1) Length : Standard metre is defined in terms of wavelength of light and is called atomic standard of length. The metre is the distance containing 1650763.73 wavelength in vacuum of the radiation corresponding to orange red light emitted by an atom of krypton-86. Now a days metre is defined as length of the path travelled by light in vacuum in 1/299,7792, 45 part of a second. (2) Mass : The mass of a cylinder made of platinum-iridium alloy kept at International Bureau of Weights and Measures is defined as 1 kg. On atomic scale, 1 kilogram is equivalent to the mass of 5.0188 x 1025 atoms of 6C12 (an isotope of carbon). (3) Time : 1 second is defined as the time interval of 9192631770 vibrations of radiation in Cs-133 atom. This radiation corresponds to the transition between two hyperfine level of the ground state of Cs-133.  
Catgeory: 11th Class

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