CHAPTER 1 :
PHYSICAL WORLD
SCIENCE
- The word Science originates from the Latin verb Scientia meaning ‘to know’.
- Science is a systematic approach or attempt to understand the natural phenomena in and around us with as much details and depth as possible, and use the knowledge so gained to predict, modify and control those phenomena.
THE STEPS IN SCIENTIFIC METHOD
- Systematic observations,
- Controlled experiments,
- Qualitative reasoning,
- Quantitative reasoning,
- Mathematical modeling,
- Prediction of Theories,
- Validation of Theories (Verification or falsification of theories).
PHYSICS
- Physics is a branch of Science.
- Physics is a basic discipline in the category of Natural Sciences
- Physics as a study of the basic laws of nature and their manifestation in different natural phenomena
- In Physics, we attempt to explain diverse physical phenomena in terms of a few concepts and laws.
- The two primary approaches of Physics are unification and reductionism.
- Attempting to explain diverse physical phenomena with a few concepts and laws is unification.
- An attempt to explain a macroscopic system in terms of its microscopic constituents is reductionism.
BRANCHES OF PHYSICS
SCOPE OF PHYSICS
- Development in technology has been quite synonymous with advances in physics, and this has, over the years, influenced society beyond our wildest imagination.
- The indelible role of physics in society is thus wholly undeniable.
- Such influences and subsequent advancements could broadly be categorized as falling under two major categories - Macroscopic and Microscopic.
- The microscopic influence includes all phenomena related to atomic, molecular, and nuclear advancements.
- The macroscopic consists of everything within the ambit of laboratory testing, practical effects and advancements, and astronomical associations.
- As evident, these two categories are overlapping at times, and it is only through a close association between these two areas that the age of technology, as we know it today, has come to be.
- The macroscopic domain includes phenomena at the laboratory, terrestrial and astronomical scales.
- Classical Physics deals mainly with macroscopic phenomena and includes subjects like Mechanics, Electrodynamics, Optics and Thermodynamics.
- Mechanics -founded on Newton’s laws of motion
- Electrodynamics – deals with electric and magnetic phenomena associated with charged and magnetic bodies.
- Optics – deals with the phenomena involving light
- Thermodynamics. – it deals with systems in macroscopic equilibrium and is concerned with changes in internal energy, temperature, entropy, etc., of the system through external work and transfer of heat.
Microscopic domain
- The microscopic domain includes atomic, molecular and nuclear phenomena.
- Quantum Theory is currently accepted as the proper framework for explaining microscopic phenomena.
Link between Technology and Physics
Physics and technology are mutually stimulated by each other; the discovery of concepts in physics is driven by technical problems, and the advancements in physics give rise to new technical problems that weren’t previously considered.
Physics and technology are interrelated. It is observed that technology gives rise to new physics and at other times physics generates new technology. Newton’s law of motion helped in the development of rockets.
Technology | Scientific principle (Physics ) |
Steam engine | Laws of thermodynamics |
Nuclear reactor | Controlled nuclear fission |
Radio and TV | Generation, propagation and detection of electromagnetic waves |
Computers | Digital logic |
LASER | Light amplification by stimulated emission of radiation |
Production of ultrahigh magnetic fields | Superconductivity |
Rocket propulsion | Newton’s laws of motion |
Electric generator | Faraday’s laws of electromagnetic induction |
Hydroelectric power | Conversion of gravitational potential energy in to electrical energy |
Aeroplanes | Bernoulli’s principle in fluid dynamics |
Particle accelerators | Motion of charged particles in electromagnetic fields |
Sonar | Reflection of ultrasonic waves |
Optical fibres | Total internal reflection of light |
Electron microscope | Wave nature of electrons |
Photocell | Photoelectric effect |
FUNDAMENTAL FORCES IN NATURE
- Gravitational force
- Electromagnetic force
- Strong nuclear force
- Weak Nuclear force
Gravitational force
- Force of mutual attraction between two weak bodies due to their masses.
- It is a universal force.
- It is a non-contact force.
- It obeys the inverse square law.
- It is the weakest of all forces.
- It is a very long range force.
- It is independent of any intervening medium.
Electromagnetic force
- It is the force between two charged particles.
- It may be repulsive or attractive in nature.
- It depends on the intervening medium.
- It is larger as compared to the gravitational force.
- It acts over large distances.
- The Electrostatic repulsive force between two protons, for example, is 1036 times the gravitational force between them, for any fixed distance.
- The forces like ‘tension’, ‘friction’, ‘normal force’, ‘spring force’, etc. are electromagnetic in nature.
Explanation:
Friction is originated from Electromagnetic forces and Exchange forces between atoms and molecules.
Electromagnetic forces and Exchange forces (or strong forces) are two of the four Fundamental forces; i.e., strong force, electromagnetic force, weak force and gravity. The causes of the resistive force of friction are molecular adhesion ,which is electromagnetic in nature, surface roughness, and the plowing effect.
Adhesion is the molecular force resulting in when two materials are brought into close contact with each other.
Surface roughness is a factor in friction when the materials are rough enough to cause serious abrasion.
A plowing effect comes into existence when one or more of the materials is relatively soft, and much of the resistance to movement is caused by deformations or this plowing effect.
So, Electromagnetic forces are involved. But the way bonds are made and broken again and again, the force is non conservative.
Strong nuclear force
- The strong nuclear force binds the nucleons or protons and neutrons in a nucleus.
- It is attractive in nature.
- It is the Strongest force in nature, which is about 100 times the electromagnetic force in strength.
- It is Charge-independent in nature and acts equally between a proton and a proton, a neutron and a neutron, and a proton and a neutron.
- It is a very short range force, which operates at about nuclear dimensions.
- You will know more of it as you get to study Yukawa Theory.
Weak nuclear force
- Weak Nuclear Force appears only in certain nuclear processes such as the β-decay of a nucleus.
- In β-decay, the nucleus emits an electron and an uncharged particle called neutrino.
- The electron and neutrino interact through weak force.
- It is of course not as weak as the gravitational force, but much weaker than the strong nuclear and electromagnetic forces.
- The range of weak nuclear force is exceedingly small, which is of the order of 10-16m.
Ratio of strengths of forces
Strong force > Electromagnetic force> Weak Nuclear force > Gravitational force
The ratio of strengths is 1: 10-2: 10-13: 10-39
Facts on Some Remarkable Researches in Physics:
Millikan's Oil drop Experiment:
Cosmic rays were discovered by Victor Hess in 1912 in balloon experiments, for which he was awarded the 1936 Nobel Prize in Physics. Victor Franz Hess (24 June 1883 – 17 December 1964) was an Austrian-American physicist.
Cosmic rays are high-energy protons and atomic nuclei that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own galaxy, and from distant galaxies. Upon impact with Earth's atmosphere, cosmic rays produce showers of secondary particles, some of which reach the surface, although the bulk is deflected off into space by the magnetosphere or the heliosphere.
In the year 1928, C.V.Raman made a discovery of the inelastic scattering of photons from the molecules such that their excitement takes place to higher levels known as Raman scattering or Raman effect.
Rayleigh scattering of light is a type of elastic scattering as the particle from which the scattering has to be done depends on the wavelength of light.
Depending on the wavelength, certain particles are more effective than others which scatter light having more wavelength, as the particles like molecules of oxygen, nitrogen having small size scatter light with a shorter wavelength (blue or violet) in different directions. The blue sky on a clear sunny day is also the result of Rayleigh scattering by the air molecules.
During the 1880s and ’90s scientists searched cathode rays for the carrier of the electrical properties in matter. Their work culminated in the discovery by English physicist J.J. Thomson of the electron in 1897.
Natural Radioactivity Radioactivity was discovered by French physicist Antoine Becquerel in 1896. He found that certain compounds of uranium emitted invisible radiations which affected photographic plates.
X-rays were discovered on November 8, 1895, by German physics professor Wilhelm Conrad Röntgen at the University of Würtzburg in Germany. He studied electric discharges in glass tubes filled with various gases at very low pressures.
In these experiments, Röntgen had covered the tube with some black paper and hand darkened the room. He then discovered that a piece of paper painted with a fluorescent dye would glow when he turned on the high voltage between the electrodes in the tube at some distance from the tube. He realized that he had produced a previously unknown “invisible light,” or ray, that was being emitted from the tube and a ray capable of passing through the heavy paper covering the tube. Röntgen referred to the radiation as “X” to indicate that it was an unknown type of radiation.
In 1924 Louis de Broglie introduced the idea that particles, such as electrons, could be described not only as particles but also as waves.
In 1899, Max Planck revived the idea that light was granular. He postulated that radiation is emitted as discrete packets of energy, with energy given by, E = h f .
In 1913, Bohr introduced his model of the hydrogen atom.
The model simultaneously explained why the light emitted by hydrogen has very sharp emission lines and why electrons don’t continuously lose energy while orbiting the nucleus. It is based on Planck’s theory of quantized radiation. Bohr stated that electrons could gain or lose energy only by absorbing or emitting photons of specific energy given by E = h f.
Unification of the observable phenomena of gravity on Earth with the observable behaviour of celestial bodies in space was done by Sir Isaac Newton .
Paul Dirac made fundamental contributions to the early development of both quantum mechanics and quantum electrodynamics. Among other discoveries, he formulated the Dirac equation which describes the behaviour of fermions and predicted the existence of antimatter. Dirac shared the 1933 Nobel Prize in Physics with Erwin Schrödinger "for the discovery of new productive forms of atomic theory". He also made significant contributions to the reconciliation of general relativity with quantum mechanics.
Unification of magnetism, electricity, light and related radiation was done by James Clerk Maxwell.
The "second great unification" was James Clerk Maxwell's 19th century unification of electromagnetism. It brought together the understandings of the observable phenomena of magnetism, electricity and light (and more broadly, the spectrum of electromagnetic radiation). This was followed in the 20th century by Albert Einstein's unification of space and time, and of mass and energy.
Later, quantum field theory unified quantum mechanics and special relativity.
Newton's Contributions
He also formulated an empirical law of cooling, made the first theoretical calculation of the speed of sound, and introduced the notion of a Newtonian fluid.
Newton formulated the laws of motion and universal gravitation that formed the dominant scientific viewpoint until it was superseded by the theory of relativity.
Newton used his mathematical description of gravity to derive Kepler's laws of planetary motion, account for tides, the trajectories of comets, the precession of the equinoxes and other phenomena, eradicating doubt about the Solar System's heliocentricity. He demonstrated that the motion of objects on Earth and celestial bodies could be accounted for by the same principles.
Emile Reynaud invented the praxinoscope and the first projected animation and the use of the first instance of film perforations.
Johannes Gutenberg ,a German Goldsmith and inventor of the printing press introduced it in Europe. His Introduction of mechanical movable type printing in Europe started the Printing Revolution.
He funded to institute the famous Nobel Prize in Stockholm, Sweden. The synthetic element Nobelium was named after him.
William Ramsay was a Scottish Chemist who won the Nobel Prize in Chemistry in 1904 for the discovery of the noble gases. His work thereby helped in the development of a different section – Noble Gases in the periodic table.
Lewis Waterman ,founder of the Waterman Pen Company. His invention and developing the pen with a simplified feed of his own design and “three fissure feed” was the first patent, granted in 1884.
Thomas Edison was an American inventor and businessman. He is considered the United States’ greatest inventor of all time who developed the electric power generation, gramophone, sound recording, and motion pictures.
Richard Gaffing ,an American inventor who is best known for its invention of the Gatling gun. This is the first successful machine gun. He also invented the screw propeller and a wheat drill (in 1893), the hemp brake machine, steam tractor, marine steam ram, and a tractor as well.
Alexander Graham Bell was an inventor, scientist, and engineer who is patented with founding the first practical telephone. He also co-founded American Telephone and Telegraph Company (AT&T) in 1885.
He contributed significantly in fields of optical telecommunications, hydrofoils, and aeronautics.
Dr. Felix Hoffman , a German Chemist is known for re-synthesizing diamorphine. He was also known for synthesizing aspirin even though he did not do it under his own name. Hoffman considered himself to be the first person to invent aspirin. He worked at Bayer, the company.
Elisha G. Otis ,an American industrialist was the founder of Otis Elevator. He was the inventor of the elevator in the year 1852.
