Chapter 1
=> Need of measurement and unit in engineering and science
The main purpose of measurement in engineering and science is to determine whether job has been manufactured to the requirement of specification . Measurement is compulsory part of development technology. Accuracy of measurement depends on :
• method of measurement
• measuring instrument.
System of units
The system of units which are in use are
1)CGS system : in this system , the units of length , mass and time are Centimeter , Gram & Second.
2) MKS system : In this system, the units of length , mass and time are Meter, Kilogram & Second.
3)FPS system : In this system, the units of length , mass and time are Foot,Pound & Second
4)SI system : S.I is the abbreviation of the french name System Internationale
=> 7 fundamental physical quantity
Quantity=> unit=> Symbol
1. Length => meter => m
2. Mass => Kilogram => kg
3. Time => second => s
4. Electric current => ampere => A
5. Temperature => kelvin => K
6. Luminous intensity=> candela=> cd
7. Amount of substance => mole => mol
=> Supplementary units
Quantity => unit => Symbol
1. Plane angle => radian => rad
2. Solid angle => steradian => sr
=> Least count and range of the instrument
Def : least count of the instrument is the smallest possible reading which can be measured accurately using that instrument.
1. Range of the instrument : It is the minimum to maximum reading that can be measured accurately using that instrument.
2. Least count = smallest division on main scale / total number of divisions on vernier scale
3. Accuracy,precision , error and estimation of errors
Define Accuracy : accuracy is the agreement of the result of a measurement with the true value of the measured quantity.
Define of precision : Precision is defined as the repeatability of a measuring process.
Error : An error is a fault, which may occur even in the most careful observation. Error arises due to human limitations and instrumental limitations. Error cannot be completely eliminated but can be reduced. Error is deviation of measurement from standard value.
1. Instrumental or constant error : This error is caused due to faulty instrument.
2. Systematic error : this error is caused due to defective settings or adjustment or unsystematicness of the experimenter.
3. Random error : This error is caused due to changes in experimental conditions,human limitations.
4. Absolute errors : The difference between the corrected reading and the mean reading is called 'Absolute error'
5. Average absolute error : The mean of absolute errors is known as 'Average absolute error'
Significant figures
• Def : A significant figure is defined as a figure in any place which is reasonably trustworthy.
Significant digits
• Def : Digits that are meaningful in assigning a true value or realistic value to a result.
The main purpose of measurement in engineering and science is to determine whether job has been manufactured to the requirement of specification . Measurement is compulsory part of development technology. Accuracy of measurement depends on :
• method of measurement
• measuring instrument.
System of units
The system of units which are in use are
1)CGS system : in this system , the units of length , mass and time are Centimeter , Gram & Second.
2) MKS system : In this system, the units of length , mass and time are Meter, Kilogram & Second.
3)FPS system : In this system, the units of length , mass and time are Foot,Pound & Second
4)SI system : S.I is the abbreviation of the french name System Internationale
=> 7 fundamental physical quantity
Quantity=> unit=> Symbol
1. Length => meter => m
2. Mass => Kilogram => kg
3. Time => second => s
4. Electric current => ampere => A
5. Temperature => kelvin => K
6. Luminous intensity=> candela=> cd
7. Amount of substance => mole => mol
=> Supplementary units
Quantity => unit => Symbol
1. Plane angle => radian => rad
2. Solid angle => steradian => sr
=> Least count and range of the instrument
Def : least count of the instrument is the smallest possible reading which can be measured accurately using that instrument.
1. Range of the instrument : It is the minimum to maximum reading that can be measured accurately using that instrument.
2. Least count = smallest division on main scale / total number of divisions on vernier scale
3. Accuracy,precision , error and estimation of errors
Define Accuracy : accuracy is the agreement of the result of a measurement with the true value of the measured quantity.
Define of precision : Precision is defined as the repeatability of a measuring process.
Error : An error is a fault, which may occur even in the most careful observation. Error arises due to human limitations and instrumental limitations. Error cannot be completely eliminated but can be reduced. Error is deviation of measurement from standard value.
1. Instrumental or constant error : This error is caused due to faulty instrument.
2. Systematic error : this error is caused due to defective settings or adjustment or unsystematicness of the experimenter.
3. Random error : This error is caused due to changes in experimental conditions,human limitations.
4. Absolute errors : The difference between the corrected reading and the mean reading is called 'Absolute error'
5. Average absolute error : The mean of absolute errors is known as 'Average absolute error'
Significant figures
• Def : A significant figure is defined as a figure in any place which is reasonably trustworthy.
Significant digits
• Def : Digits that are meaningful in assigning a true value or realistic value to a result.