Introduction

A standard unit system is important for uniformity in measurement. Units and Measurements are a comparison tool to assert a theory’s validity. Units and Measurements of Class 11 Notes include in-depth information about different types of standard units, measurements, and dimensions used worldwide. 

Physical Quantity

The quantity that can be measured and in which the laws of physics are expressed is called a Physical Quantity. For example, length, time, mass, temperature, etc. 

Units and Measurements

The comparison of physical quantities in terms of numerical value is referred to as Measurement. 

An internationally recognized standard to measure the physical quantity is called the Unit. 

Properties of Units

1. A unit should be well defined
2. A unit should not change with time and place
3. A unit should not change with physical conditions such as pressure, temperature, etc. 

Types of Unit

 There are two types of units: Fundamental Units and Derived Un

Fundamental Units

The standard unit used to define fundamental quantities is called the fundamental Units.  

Quantity	Unit	Symbol
Length	Metre	M
Time	Second	S
Mass	Kilogram	Kg
Electric current	Ampere	A
Temperature	Kelvin	K
Quantity or amount	Mole	mol
Luminous intensity	Candela	Cd

Supplementary Fundamental Units

Quantity	Unit	Symbol
Plane angle	Radian	rad
Solid angle	Steradian	Sr

Derived Units

 Derived Units are a SI unit of measurement that consists of two or more of the fundamental units. Example: Force, Resistance, speed, density, etc. 

Systems of Units

There have been several systems of units of measurement for physical quantities for years. The logical and international System of Units is used in contemporary times. 

Systems of Units	Unit of Length	Unit of Weight	Unit of Time
FPS	Foot	Pound	Second
CGS	Centimetre	Gram	Second
MKS	Metre	Kilogram	Second
SI	Metre	Kilogram	Second

Definitions of SI Base Units

Let’s go through the definition of the SI-based units in detail.

• Metre

 Metre is the distance travelled by light in a vacuum in a second, and it is expressed as m.s

• Second

The duration of 9192631770 vibrations corresponds to the transition between two hyperfine levels of the ground state of cesium-133 atoms. 

• Kilogram

It is a SI unit of mass, and it can be defined as the mass of a platinum-iridium cylinder kept in the National Bureau of Weights and Measurements in Paris.  

• Ampere

Ampere is defined as the flow of one coulomb of electricity per second. 

• Kelvin 

Kelvin is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. 

• Mole

Mole can be defined as 6.02214076 x 10^23 of a substance.

• Candela

It expresses the luminous intensity of visible light. It measures the luminous power per unit solid angle emitted by a source of light in a specific direction. 

Dimensions and Dimensional Formula

1. Dimensions– A dimension is the fundamental nature of a physical quantity, such as mass, time, etc. 
2. Dimensional Formula– It is an expression of how the fundamental dimensions are combined to define a derived quantity. 
3. Dimensional Equation- Dimensional Equation is formed by equating a physical quantity with its dimensional formula. Understanding the relationship between the fundamental dimensions that form a physical quantity. 

• Dimensional Formula of a Physical Quantity

1. The formula must be written in terms of fundamental quantities such as time, mass, etc.
2. Mass, length, and time must be replaced by M, L, and T. 
3. The power of the terms must be written. 

Physical Quantity	Dimensional Formula
Volume	[M0L3T0]
Speed	[M0LT-1]
Force	[MLT-2]
Mass Density	[ML-3T0]

• Characteristics of Dimensions

1. Dimensions are expressed numerically in terms of relevant parameters. 
2. Dimensions do not depend on the system of units. 
3. Two different quantities can have the same dimension. 

• Application of Dimensional Analysis

1. We can check the accuracy of an equation
2. We can convert the physical unit from one to another.
3. Algebraic quantities can be used to express dimensional expressions. 

• Principle of Homogeneity

The principle of homogeneity states that the dimensions of each term of a dimensional equation on both sides must be the same. This principle helps to convert the units from one form to another. 

• Limitations of Dimensional Analysis

1. As different physical quantities can have the same dimension, it is difficult to determine the uniqueness of the physical quantity. 
2. Any information about the dimensional constant can not be obtained
3. The complex functions, like trigonometric, logarithmic, can not be derived by using dimensional analysis. 
4. Dimensional analysis can not identify all the variables that influence a specific physical quantity. 

Units and Measurements of Class 11 notes of Learn Physics with Ease is a valuable resource for understanding the fundamental concepts of physics. We provide updated study materials that include clear explanations and examples to clarify your concept in this chapter. Our CBSE Class 11 Physics Units and Measurements notes condense complex concepts in concise summaries. 

Conclusion

The Units and Measurements of Class 11 notes offer a detailed and comprehensive explanation of the concepts of Units and Measurements. It includes a brief description of units and dimensions. The practice sets, study materials, and mock tests Learn Physics with Ease help the students to improve their understanding of this chapter. The guidance of  Learn Physics with Ease is essential to achieve excellence in physics and improve exam scores.

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