UNITS AND MEASUREMENTS Class 11 Formulae for KCET
Physical and Non Physical Quantities
Physical Quantities : Those quantities whose value can be measured in physics are called as physical Quantities.
Example: length , mass and time
Non Physical Quantities : Those Quantities in physics whose value cannot be measured are called as Non Physical Quantities.
Example : Love, Anger , Sadness etc
Units : Unit is a fixed quantity in reference to which all the other quantities are measured.
Example : 1 meter, 1 second etc
System of Units
Earlier in different parts of the world, Different units were being used for measuring a particular quantity.
MKS System
M represents meter is used to measure length
K represents kilogram is used to measure Mass
S represents second is used to measure Time
CGS System
C represents centimeter is used to measure length
G represents grams is used to measure mass
S represents second is used to measure Time
FPS SYSTEM
F represents foot is used to measure length
P represents pound is used to measure mass
S represents second is used to measure Time
Note : Due to varies conflicts in measurements a common system of units called International System of Units was made which is called SI Units
Fundamental Units
- Length – m ( meter )
- Mass – kg ( kilogram )
- Time – s ( second )
- Current – A ( Ampere )
- Temperature – K ( Kelvin )
- Luminous Intensity – cd ( candela )
- Amount of Substance – mol ( mole )
Supplementary Units
1 Radian : The angle subtended at the center by an arc whose length is exactly equal to the radius is said to be 1 radian.
1 Steradian : The angle subtended at the center of a sphere by an area whose value is exactly equal to the radius of the sphere.
Measurement of Length, Mass and Time
Measurement of Length
The measurement of length is done by using a meter scale. Where the least distance that can be measured is 1mm.
However, For measuring smaller distances of the order of 0.1mm we can use vernier caliper. For greater precision we can use screw guage which can be used to measure the value as small as 0.01mm.
Measurement of Mass
Mass is basically the quality of matter contain in a body . It is measured in terms of Kilograms
Measurement of Time
A clock is used to measure time and the SI unit of time is second. However, Now we use a cesium clock or which is also known as atomic clock to measure time.
In cesium clock the time is based on periodic vibrations of the cesium atom.
Error , Accuracy and Precision
Error : The uncertainty in the measurement of a quantity is called as error.
Accuracy : Accuracy in a measurement means how close a measured value is to the true value.
Precision : Precision tells us to what limit of resolution a quantity can be measured. It basically tells the fineness of the measuring instrument.
Dimensions
The dimensions of a physical quantity are the powers to which fundamental quantities are raised to represent that quantity.
Applications of Dimensional Analysis
- Conversion of a unit from one system to other system
- Checking correctness of the equation
- Also, Deriving new relations
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About this Notes
So, this is notes for the chapter units and measurements formulae. And, It basically consist of all the formulae from this chapter from class 11 physics. Moreover, It also consist of Theory part for Quick revision.
However, it does not contain any numerical for practice and only contains the synopsis. So, do practice proper amount of numerical problems for this chapter.
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