Home | Courses | Back to Chapter | Any Question? |

Physics - 11 Complete Syllabus Notes

Chapter 1 - Unit and Dimension

Classical Mechanics:
It deals with objects from molecules to galaxies moving with speed small as compare to the speed of light. Classical Mechanics is also called Newtonian Mechanics.

Measurement:

Measurement is the comparison of unknown physical quantity with known fixed unit quantity.
Physical Quantity can be expressed as:

Physical Quantity = Numerical value x Unit
Q = nu

Physical Quantity can vbe divided into two quantities i.e. fundamental and derived quantities

Fundamental Quantities:
The physical quantities which doesn't depend on other quantities are called fundamental quantities.
Examples: Length, mass, time etc.

Derived Quantities:
The physical quantities which depend on other quantities are called derived quantities.
Examples: force, speed, energy

Unit:
The quantity used as a standard of measurement is called a unit.

Derived Unit:
The unit of derived quantity is called derived unit.
Examples: m/s, m/s2, energy

Fundamental Unit:
The unit of fundamental quntity is called fundamental unit.
Examples: kg, meter, seconds.

System of Unit:

  • FPS System: The system of unit in which length in foot, mass in pound and time in second.

  • CGS System: The system of unit in which length in centimeter, mass in gram and time in second.

  • MKS System: The system of unit in which length in meter, mass in kilogram and time in second.

S.I System:
The extended form of MKS System in which length in meter, mass in kilogram and time in second, Electric Current in ampere, temperature in kelvin, amount of substance in mole and luminous intensity in candela.
There are two sublimentary quantities they are plane angle and solid angle and unit are Radian and Steradian.

Advantage of S.I System:
i) It is coherent system of unit.
All the derived SI unit are expressed by multiplying and dividing based SI unit without introducing numerical factor.

ii) It is rational system of unit.
It uses same unit for same physical quantities.
Examples: All energy are measured in joule.

Dimension:
The dimension of a phusical uantity is defined as the power to be raised in the fundamental quantities in ordered to represent the physical quantities.
If a physical quantity is expressed in terms of dimension then it is called dimensional formula.

Mass = [M]
Length = [L]
Time = [T]

Example:
Speed = (distance travelled ) / time taken
Speed = [L] / [T]
Speed = [ L T-1]
Speed = [ M0 L T-1]

Therefore, Dimensional Formula of speed is [M0 L T -1] and dimension of speed is 0 in mass, 1 in length and -1 i time.
#find the dimensional formula of specific heat capacity and universal gravitational constant.
hint: specific heat capacity(Q) = msdt and G = F × ( M1 × M2 ) / d2

Physical Quantities are divided into four catagories in dimensuional analysis:
i) Dimensional Variables
ii) Dimensional Constants
iii) Dimensionless Variable
iv) Dimensionless Constant
  • Dimensional Variable:
    The physical quantities having dimensions and are variables are called dimensional variables. eg: Speed, Work, Power etc.

  • Dimensional Constant:
    The physical quantities having dimensions with fixed values are called dimensional variables. eg: Speed, Work, Power etc.

  • Dimensionless Variable:
    The physical having no dimension and are variables are called dimensionless variable . eg: Angle, Strain, Specific gravity.

  • Dimensionless Constant:
    The quantities having no dimensions and are constant are called dimensionless constant. . eg: pie, counting number.
Uses of dimensional formula:(application)
i) To check the correctness of given physical equation. As per principle of homogeneity, the dimension of physical quantity on either side of equation must be same.

ii) To find the dimensional formula of dimensional constant. FOr example: In equation E = hf, E is the energy, F is the frequwncy and h is the plank constant, the with the help of dimensional formula we can find h.

iii) To convert the one system of unit into another system. Example: we can convert N to dyne.
iv) To derive a physical equation.

Drawbacks of dimensional formula:
i) It gives no information about dimensionless constant.
ii) It gives no information about whether a physical quantity is scalar or vector.
iii) We cannot derive equation containing trigonometric function, exponential function.
iv) The exact form of equation cannot be develop if it contain more than one part.

Significant Figures:
The number of digits in a measurement in which we are certain plus one additional digit in which we are uncertain are called significant figures.
For example: In 12475 kg the significant figure is simply 5 likewise in 6.2 × 102 m the significant figure is 3.

Accuracy of Measurement:
If the measured value of a physical quantity in the measurement is close to true value or exact value and the measurement is Accuracy of measurement. Good accuracy means measured is close to true value.

Precision of Measurement:
The limit up to which the physical quantity is measured is called precision of measurement. Good Precision means measured value is close to mean value.
#try to find differences between accuracy and precision


In case of any problem ask me in qustions section!!!!

© 2020 onlinelearnal.com