## Physical Quantities Physics Notes

Physical Quantities:
A physical quantity is a quantity that can be measured and expressed in numbers and units.
For example: Mass, length, time, force, velocity etc.

Physical quantities are of two types:
1. Fundamental quantities: Fundamental units are those units, which can neither be derived from one another nor can they be further resolved into any other units. The quantities mass, length and time are called fundamental physical quantities and their units are known as fundamental units because:

1. Mass, length and time can not be obtained from one another.
2. All other physical quantities in mechanics can be – obtained from them. 2. Derived quantities: The units of all such physical quantities, which can be expressed in terms of the fundamental units of mass, length and time are called derived units. For example force, work, power, energy, pressure, momentum, acceleration, density etc. are all derived units and they can be obtained by writing their defining equations in terms of fundamental physical quantities. To explain, let us consider the defining equation of speed,

we know that:
Speed = $$\frac{\text { Distancecovered }}{\text { Timetaken }}$$

So, unit of speed
= $$\frac{\text { Unitof distance i.e.length }}{\text { Unit of time }}$$
= $$\frac{\text { meter }}{\text { second }}$$ = m/s

## Contribution of Physics in Technology and Society Physics Notes

→ Contribution of Physics in Technology and Society:
Physics is making a tremendous contribution to the social progress of mankind and hardly any branch of science can sustain and progress without making use of the techniques of modern physics.

Physics is the most basic of all the sciences and it has played a very important role in the development of other sciences as Chemistry, Astronomy, Geology, Meteorology, Oceanography and Seismology. Biological sciences have also been benifited by advancement in physics. Optical microscope and electron microscope has made it possible to see the structure of a cell.

Some of the applications in physics based on modern technology are:

1. The discovery of electromagnetic induction by Faraday can be regarded as one of those great scientific discoveries, which have not only benefited the common man but have formed the basis of the technology.
2. Radio, television, fax, wireless etc. are based on the propagation of electromagnetic waves. The study of satellites has made it possible to forecast weather very accurately.
3. Discovery of X-ray has immense use in medical science.
4. The discovery of nuclear fission has proved to be a tremendous source of energy. In nuclear power station and nuclear bombs, a large amount of energy becomes available due to conversion of mass into energy.
5. Flight of aircrafts is based on Bernoulli’s principles.
6. Conversion of heat energy into mechanical work has lead us to design diesel engine, petrol engine steam engine etc. These are based on the laws of thermodynamics. Physics in relation to society:
The fate of society is intimately linked to physics. It is because, whatever is thought or discovered in physics, it immediately affects society. The advancement in the field of communication, such as telephone, teleprinter and telex enables us to quickly exchange messages between far off places. The radio and television have made it possible to instantly communicate with other parts of the world. Silicon chip technology has triggered the computer revolution, in last three decades of the twentieth century.

Microelectronics, lasers, computers, super conductivity and nuclear energy have brought about a profound change in the thinking and living style of the human beings.

## Requirement of Measurement Physics Notes

Requirement of Measurement:
For the description of any natural phenomenon, measurement of the involved quantities is important. We realise the need of measurement, in every physical situation.

For example, when an apple falls from a tree it falls freely on the surface of the earth. In this situation, one may want to know with what velocity the apple reaches the ground, in how much time does it reach the ground etc. To know these, one must know how to measure distance and time. Electric bulb is commonly used. It glows by consuming electric energy. The measurement of energy consumed is very important.

When we feel unwell, we measure the temperature from a thermometer. Blood pressure, heart beat etc. are also measured primarily.

## What is Physics? Notes

We are surrounded by physics all the time, and whether we realize it or not, we use physics every day.
Physics the study of matter and energy is an ancient and broad field of science.

The word ‘Physics’ comes from the Greek word ‘Fusis’ meaning ‘Knowledge of nature’ and in general, the field aims to analyze and understand the natural phenomena of the universe.

Though there are many definitions of physics, yet it can be defined as, “The study of the properties of matter, energy and their mutual relationship. ”

Scope and Expansion of Physics:
Physics is the branch of science, which deals with the properties of matter and energy and the relationship between them. It also tries to explain the material world and the natural phenomena of the – universe. The scope of physics is very wide and vast. It deals with not only the tiniest particle of atoms but it also dwells upon the natural phenomenon like galaxy, milky way, solar and lunar eclipse, etc. Branches of Physics:

→ Branches of Physics
Physics is broadly classified into two parts.
(A) Classical physics
(B) Modern physics.

1. Macroscopic physics: Under macroscopic, physics comes the astronomical and earth-related incidents. The principles of classical mechanics clearly define macroscopic physics.

2. Microscopic physics: Microscopic physics covers the molecular, atomic and nuclear incidents. Quantum mechanics is studied to understand microscopic physics.

3. Mesoscopic physics: It is a subdiscipline of condensed matter physics that deals with materials of an intermediate length. The scale of these materials can be described as being between the size of a quantity of atoms (such as a molecule) and of materials measuring micrometers.
(A) Classical physics: Classical physics includes the traditional branches and topics that were recognized and fairly well developed before the beginning of the 20th century. It is mainly concerned with the laws of motion and gravitation by Sir Isaac Newton and a kinetic theory and thermodynamic by James Clark Maxwell. Classical physics is mainly concerned with matter and energy. In this branch, energy and matter are considered as separate entities.

Classical mechanics, Optics, Acoustics and Electromagnetics are the traditional branches of classical physics.
1. Mechanics: Mechanics is the study of physics of motion and how it relates to the applied forces. It lays the foundation of understanding the world around us through the question of how and why a thing moves. 2. Thermodynamics: Thermodynamics is the branch of physics, which deals with the study of heat and its relation with energy and work. This branch also deals with the study of gaseous systems. The change in temperature, internal energy and entropy of the system through external work are investigated. Modes of transfer of heat, efficiency of heat engines and refrigerators are also included in thermo¬-dynamics.

3. Electromagnetism: Electromagnetism is a branch of physics involving the study of electricity, magnetic effect and electromagnetic waves i. e., it deals with the study of electromagnetic force, a type of physical interaction that occurs between electrically charged particles. The electromagnetic force usually exhibits electromagnetic field such as the electric field, the magnetic field and light.

4. Acoustics: The word acoustics has been derived from a Greek word ‘akouen’, meaning ‘to hear’. Hence we can define acoustics as a branch of physics, which studies how sound is produced, transmitted, received and controlled. It also deals with the effects of sounds in various mediums t.e, gases, liquids and solids.

5. Optics: Optics involves the study of various phenomena connected with light and optical instruments like microscope, telescope etc. The topics studied in optics include images formed by lenses and mirrors, reflection, refraction, interference, diffraction, dispersion and polarization of light. (B) Modern physics: Modern physics is the branch of physics, which is mainly concerned with the theory of relativity and quantum mechanics. Albert Einstein and Max Plank were the pioneers of modern physics.

1. Relativity: Relativity is concerned with the study of those bodies that move with the speed almost the same as the speed of light.
2. Quantum Mechanics: In quantum mechanics, we study about modern principles of physics, dual nature of light and particles etc.
3. Atomic Physics: Atomic physics is the branch of physics which deals with the composition of atom apart from nucleus. It is mainly concerned with the arrangement and behaviour of electrons in shells around the nucleus.
4. Nuclear Physics: Nuclear physics is the branch of physics which deals with constituents, structure, behaviour and interaction of atomic nuclei. In the modern age, nuclear physics has got a very wide scope. It is used in power generation, nuclear weapons, medicines etc.

Apart from these branches, there are many branches of physics. Some of them are… Bio Physics, Electronics, Plasma-Physics, High Energy Physics, Astrophysics, Condensed Matter Physics, Solid State Physics, Environmental Physics, Computational Physics, Polymer Physics, Materials Physics and Cryogenics.

## Physical World and Measurement Physics Notes

→ We are living in the age of science. The cell phoney television, computer, e-mail, internet, audio-video system, e-mail, car, bus, train… all are the gifts of science to humans. Every field of human activity, is influenced by science.

The word science comes from the Latin verb ‘Scientia’ meaning ‘to know’. Science refers to a system of acquiring knowledge. This system uses observation and experimentation to describe and explain natural phenomena.

The term science also refers to the organised body of knowledge, people have gained using that system. Less formally, the word ‘science’ often describes any systematic field of study or the knowledge gained from it.

→ Fields of science are commonly classified along two major lines:

• Natural Sciences, the study of the natural world.
• Social Sciences, the systematic study of human behaviour and society.

→ The science that deals with non-living things is called Physical Science e.g., Physics, Geology, Chemistry, Astronomy, Oceanology, Astrology, Geography etc.

→ The science that deal with living things is called Biological Science. For example, Zoology, Botany, Anthropology, Entomology, Forensic Science etc. → Physics: It is the branch of science in which we study about nature and natural phenomena.

→ Unit: The chosen standard of the same kind taken as a reference to measure a physical quantity is called the unit of that quantity.

→ Fundamental unit: Those units, which can neither be derived from one another, nor can they be further resolved into other units, are called fundamental units.
The units of mass, length and time are called fundamental units.

→ Derived units: The units of all such physical quantities, which can be expressed in terms of fundamental units of mass length and time are called derived units.

→ Standard unit: A standard unit should be well defined, of suitable size, easily reproducible, easily accessible, should not change with time and also from place to place and with change in physical conditions, (temperature, pressure etc.)

→ Systems of units:

• M.K.S. system
• CGS system
• FPS system
• SI

→ SI: It consists of seven basic units namely metre, kilogram, second, kelvin, ampere, candela, mole and two supplementary units namely radian and steradian.

→ Dimension: Dimensions are powers raised on fundamental units to represent the physical quantity.

→ Dimensional formula: The relation of M, L and T with its dimensions to represennt the physical quantity is called dimensional formula.

→ Dimensional equation: The equation obtained, when a physical quantity is equated with its dimensional formula is known as dimensional equation.

→ Principle of homogeneity of dimensions:
It states that the dimensions of the fundamental quantities are same in-ear, a and every term one either side of physical relation. → Uses of the dimensional equation:
(A) To check the correctness of a physical relation. It is based on principle of homogeneity of units.

(B) To derive the relation between different physical quantities involved in a physical phenomenon.
It is also based on the principle of homogeneity of units.

(C) To convert on a system of unit to another.
Mathematically: n2 = n1$$\left(\frac{m_{1}}{m_{2}}\right)^{a}\left(\frac{L_{1}}{L_{2}}\right)^{b}\left(\frac{T_{1}}{T_{2}}\right)^{c}$$

→ The constant such as integers (1, 2, 3…., n and c do not have dimensions, (dimensional constant)

→ A physical constant may posess dimensions.

→ A physical variable may not possess dimensional (dimension less variable). For example angle (plane or solid) T-ratios, specific gravity, strain, refractive index, power factor, relative permittivity and relative permeability.

→ A dimensional physical quantity may possess units. For example angle is dimensionless but it has got units.

→ A physical quantity having dimensions must possess units.

→ Significant figures: The digits, whose values are accurately known in a particular measurement are called its significant figures.

→ Significant figures in calculations: Do not retain a greater number of decimal places in a
result computed from addition and/or subtraction or multiplication and/or division than in the observation which has the fewest decimal places. → Errors in measurement:

1. Constant error: When the result of a series of observation are in error by same amount the error is said to be a constant one. It is because of the inbuilt error in the measuring instrument.
2. Systematic error: A systematic error is one that produces an error of same sign. The zero error in instruments, error due to variation in physical condition or the personal error are the causes of systematic errors.
3. Random errors: The errors due to unknown causes are called random or chance errors. It is eliminated by taking the arithmetic mean of a large number of observations.
4. Gross error: The error due to sheer carelessness on the part of the experimenter are called gross error.
The neglect of sources of error, reading the instrument incorrectly or recording the observation carelessly are the causes of gross errors.
5. Absolute error: The magnitude of the difference between the true value and the measured value is called absolute error.
Absolute error = True value – measured value,
6. Relative error: The ratio of the mean absolute error to the true value is called relative error Absolute error
Relative error = $$\frac{\text { Absoluteerror }}{\text { true value }}$$
Also percentage error = $$\frac{\text { Absoluteerror }}{\text { true value }}$$ ×100

→ Science: Science is the study of the nature and behaviour of natural things and the knowledge that we obtain about them.

→ Physics: Physics is the natural science that involves the study of matter and its motion and behaviour through space and time, along with related concepts such as energy and force.

→ Measurement: Measurement is the assignment of a number to characteristics of an object or event, which can be compared with other objects or events.

→ Mole: The mole is the unit of measurement for the amount of substance in the international system of units (SI.)

→ Parallax: Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. → Least count: The smallest value that can be measured by the measuring instrument is called its least count.

→ Error: An ‘error’ is a deviation from accuracy or correctness.

→ Significant digit: Each of the digits of the number that are used to express it to the required degree of accuracy, starting from the first no-zero digit.