UNIT AND DIMENSIONS
This course introduces students to the fundamental principles of physics, focusing on physical quantities, units of measurement, and the concept of dimensions. It provides a strong foundation for understanding the quantitative aspects of physical laws and their practical applications.
2. UNIT
1.2 UNITS: FUNDAMENTAL AND DERIVED UNITS
Measurement: In our daily life, we need to express and compare the magnitude of different quantities; this can be done only by measuring them.
Measurement is the comparison of an unknown physical quantity with a known fixed physical quantity.
Unit: The known fixed physical quantity is called unit. OR
The quantity used as standard for measurement is called unit.
For example, when we say that length of the class room is 8 metre. We compare the length of class room with standard quantity of length called metre.
Length of class room = 8 metre
Q = UN
Physical Quantity = Numerical value × unit Q = Physical Quantity
n = Numerical value u = Standard unit
e.g. Mass of stool = 15 kg Mass = Physical quantity 15 = Numerical value Kg = Standard unit
Means mass of stool is 15 times of known quantity i.e. Kg.
Characteristics of Standard Unit: A unit selected for measuring a physical quantity should have the following properties
(i) It should be well defined i.e. its concept should be clear.
(ii) It should not change with change in physical conditions like temperature, pressure, stress etc..
(iii) It should be suitable in size; neither too large nor too small.
(iv) It should not change with place or time.
(v) It should be reproducible.
(vi) It should be internationally accepted.
Classification of Units: Units can be classified into two categories.
1. Fundamental
2. Derived
Fundamental Quantity: The quantity which is independent of other physical quantities. In mechanics, mass, length and time are called fundamental quantities. Units of these fundamental physical quantities are called Fundamental units.
e.g. Fundamental Physical Quantity Fundamental unit
Mass Kg, Gram, Pound
Length Metre, Centimetre, Foot
Time Second
Derived Quantity: The quantity which is derived from the fundamental quantities e.g. area is a derived quantity.
Area = Length x Breadth
= Length x Length
= (Length)2
Speed =Distance /Time
=Length / Time
The units for derived quantities are called Derived Units.
1.2.1 Table of Fundamental Units
|
Sr. No. |
Name of Physical Quantity |
Unit |
Symbol |
|
1 2 3 4 5 6 7 |
Length Mass Time Temperature Electric Current Luminous Intensity Quantity of Matter |
Metre Kilogram Second Kelvin Ampere Candela Mole |
m Kg s K A Cd mol |
1.2.2Table of Supplementary unit
|
Sr. No |
Name of Physical Quantity |
Unit |
Symbol |
|
1 2 |
Plane angle Solid angle |
Radian Steradian |
rad sr |