What Is the Most Important Topic of Units and Measurement of Class 11 Physics?

The true notion of measurement, which is defined in Notes of Physics Class 11 Chapter 2, is the foundation of any issue or concept in physics. The concept of measurement is a comparison of an object’s physical attribute to a standard. Class 11 Physics Chapter 2 Notes provides a thorough understanding of all types of measurements, units, dimensions, and measurement mistakes. To measure a physical quantity, one must first determine how many times a standard measure of that amount exists in the item getting measured.


The measuring procedure is essentially a comparison process. To determine how many times a standard amount of a physical quantity is present in the quantity being measured, we must first determine how many times a standard amount of that physical quantity is present in the quantity being measured. The magnitude of the number obtained is termed the unit of the physical quantity, and the standard used is called the unit of the physical quantity.


A physical quantity’s unit is an arbitrarily determined standard that is universally recognised by society and may be used to measure other physical quantities of comparable kind.


A standard of a physical quantity is the real physical manifestation of that physical quantity’s unit. We require the numerical value (n) and the unit () to represent any measurement. Physical amount measurement = Numerical value x Unit. Consider the following scenario: A rod’s length is 8 metres. Where m (metre) is the unit of length and 8 is the numerical value.

Physical Quantity/Units at a Basic Level

It is a fundamental physical quantity that may be expressed without the need of any other physical quantity. It can’t be resolved any further in terms of another physical quantity. It’s also known as the fundamental physical quantity. Basic units are the units of fundamental physical quantities. Mass, Length, and Time are essential units of the M. K. S. system, for example, and are represented in kilogrammes, metres, and seconds, respectively.

Physical Quantity/Units Derived

The phrase “derived physical quantities” refers to all physical quantities that may be derived from the combination of two or more fundamental quantities or stated in terms of basic physical quantities. All other physical quantities’ units, which may be derived from basic units, are referred to as derived units. Units of velocity, density, and force, for example, are m/s, kg/m3, and kg m/s2, respectively, and are instances of derived units.

Units of Measurement

Previously, various countries utilised three separate unit systems. CGS, FPS, and MKS were the systems under question. Internationally, the SI system of units is now used. Seven values are used as the base quantities in the SI unit system. CGS System I The units of length, mass, and time are the centimetre, gramme, and second, respectively. FPS (First Person Shooter) System. The units of length, mass, and time are the foot, pound, and second, respectively. MKS System: The length is measured in metres, the mass is measured in kilogrammes, and the duration is measured in seconds. The units of length, mass, and time are the metre, kilogramme, and second, respectively. SI stands for International System of Units. The units of measurement for length, mass, time, electric current, thermodynamic temperature, amount of material, and luminous intensity are second, kilogramme, ampere, metre, mole, kelvin, and candela.

Units of Supplementary Instruction

There are two more base units in addition to the seven described above. The terms for angle and solid angle are I radian (rad) and (ii) steradian (sr).

The SI Unit System Has a Number of Advantages

The advantages of the SI Unit System over other systems are as follows: There are two more base units in addition to the seven described above. These are unit systems: I It is an internationally recognised unit system, it is a rational unit system, It is a coherent unit system, It is a metric system, It is closely connected to the CGS and MKS systems of units, and It uses the decimal system, making it more user-friendly.

Method of Parallax

This approach is used to calculate the distance between planets and stars. Hold a pen in front of your eyes and gaze at it by closing your right eye first, then your left. What are your observations? The pen’s location varies in relation to the background. The term parallax refers to the relative change in the location of the pen (object) with relation to the backdrop. If a distant object, such as a planet or star, subtends parallax angle 0 on an arc of radius b (known as basis) on Earth, then s = b/theta gives the distance of that distant object from the basis. The electron microscope and tunnelling microscopy techniques can be used to measure the size of atoms. We can estimate the size of nuclei of different elements using Rutherford’s a-particle scattering experiment. To tell the time, people use pendulum clocks, mechanical watches (which employ the vibrations of a balancing wheel), and quartz watches.

Solve this question: In successive measurement, the reading of the period of oscillation of a simple pendulum were found to be 2.63s, 2.56s, 2.71s and 2.80s in an experiment.


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