shahjahan notes...

1. GeniusphysicsbyShahjahan….
“Alteryourlife bythinking”
By Shahjahan…
• Science meansorganizedknowledge.
It ishuman nature to observe thingsandhappenings
aroundin the nature and thento relate them.This
knowledge isorganizedso thatitbecome well
connectedandlogical.Thenitisknownas Science.It
isa systematicattempttounderstandnatural
phenomenonanduse thisknowledge topredict,
modifyandcontrol phenomena.
ScientificMethod
Scientificmethodsare usedtoobserve thingsand
natural phenomena.Itincludesseveral steps:
• Observations
• Controlledexperiments,
• Qualitative andquantitativereasoning,
• Mathematical modeling,
• Predictionand
• Verificationorfalsificationof theories.
There is no‘final’theory inscience and no
unquestionedauthorityinscience.
• Observationsandexperimentsneedtheories
to supportthem.Sometimesthe existing
theoryisunable toexplainthe new
observations,hence eithernewtheoriesare
formedor modificationisdone inthe existing
theories.
• For example toexplaindifferentphenomena
inlight,theoriesare changed.Toexplain
bendingof lightanewWave-theorywas
formed,andthento explainphotoelectric
effecthelpof quantummechanicswastaken.
Natural Sciences can be broadlydividedinthree
branchesnamely Physics,Chemistryandbiology
• Physicsis a studyof basiclawsof nature and
theirmanifestationindifferentphenomenas.
Principal thrustsin Physics
• There are twoprincipal thrustsinPhysics;
• 1.Unification 2. reduction
Unification
• Effortsare made to explaindifferent
phenomenainnature onthe basisof one or
minimumlaws.Thisisprincipleof Unification.
Example:Phenomenaof apple fallingtoground,
moonrevolvingaroundearthandweightlessnessin
the rocket,all these phenomenaare explainedwith
helpof oneLaw that is,NewtonsLaw of Gravitation.
Reductionism
• To understandorto derive the propertiesof a
biggeror more complex systemthe properties
of itssimplerconstituentsare takeninto
account. Thisapproachis calledreductionism.
It issupposedtobe the heartof Physics.
For example acomplex thermodynamical systemcan
be understoodbythe propertiesof itsconstituentlike
kineticenergyof moleculesandatoms.
• The scopeof Physics can be dividedintotwo
domains; Macroscopicand Microscopic.
• Macroscopic domainincludesphenomenaatthe
level of Laboratory,terrestrial andastronomical
scales.
• MicroscopicdomainI ncludesatomic,molecular
and nuclearphenomena.
• Recentlythirddomaininbetweenisalsothought
of withname MesoscopicPhysics.Thisdealswith
groupof Hundredsof atoms
• Scope of physicsisverywide andexciting
because itdealswithobjectsof size aslarge
as Universe (1025
m) andas small as 10-14
m,
the size of a nucleus.
The excitementofPhysics isexperiencedinmany
fieldsLike:
• Live transmissionsthroughtelevision.
• Computerswithhighspeedandmemory,
• Use of Robots,
• Lasersand theirapplications
Physicsin relationto otherbranches of Science
PhysicsinrelationtoChemistry.
• Chemical bonding,atomicnumberand
complex structure canbe explainedbyphysics
phenomenaof Electrostaticforces,
• takinghelpof X-raydiffraction.
Physical World

2. GeniusphysicsbyShahjahan….
“Alteryourlife bythinking”
By Shahjahan…
PhysicsinrelationtootherScience
• PhysicsinrelationtoBiological Sciences:
Physicshelpsinstudyof Biologythroughits
inventions.Optical microscope helpstostudy
bio-samples,electronmicroscope helpsto
studybiological cells.X-rayshave many
applicationsinbiological sciences.Radio
isotopesare usedincancer.
•
PhysicsinrelationwithAstronomy:
• Giant astronomical telescopedevelopedin
physicsare usedfor observingplanets.Radio
telescopeshave enabledastronomersto
observe distantlimitsof universe.
• Physicsrelatedtoothersciences:Lawsof
Physicsare usedto studydifferent
phenomenasinotherscienceslikeBiophysics,
oceanography,seismologyetc.
Fundamental Forcesin Nature
There is a large numberof forcesexperienced or
applied.These may be macroscopicforceslike
gravitation,friction,contactforcesand microscopic
forceslike electromagneticand inter-atomicforces.
But all these forcesarise fromsomebasic forcescalled
FundamentalForces.
FundamentalForcesin Nature..
1. Gravitational force.
• It is due to Massof thetwo bodies.
• It is alwaysattractive.
• It operatesin all objectsof universe.
• Its rangeis infinite
It’sa weakforce.10-38
times compared to strong
Nuclearforce
2.ElectromagneticForces:
• It’sdue to stationeryormovingElectrical
charge
• It may be attractive or repulsive.
• It operatesonchargedparticles
• Its range isinfinite
• Its stronger1036
timesthangravitational force
but 10-2
timesof strong Nuclearforce.
3. Strong nuclear force:
• Operate betweenNucleons
• It may be attractive or repulsive
• Its range isveryshort, withinnuclearsize
(10-15
m).
• Its strongestforce innature
4.Weak Nuclearforce:
• Operate withinnucleonsI.e.elementary
particleslike electronandneutrino.
• It appears duringradioactive bdecay.
• Has veryshort range 10-15
m.
• 10-13
timesthanStrongnuclearforce.
ConservationLaws
• In anyphysical phenomenongovernedby
differentforces,several quantitiesdonot
change withtime.These special quantitiesare
conserved quantitiesof nature.
1.For motionunderconservativeforce,the total
mechanical Energyof a bodyis constant.
2.Total energyof a systemisconserved,anditisvalid
across all domainsof nature frommicroscopicto
macroscopic.Total energyof the universe isbelieved
to be constant.
3.Conservationof Masswas consideredanother
conservationlaw,till adventof Einstein.Thenitwas
convertedtolaw of conservationof massplusenergy.
Because massis convertedintoenergyandvice-versa
accordingto equationE = mc2
The examplesare
annihilationandpairproduction.
4.Momentumisanotherquantitywhichispreserved.
Similarisangularmomentumof anisolatedsystem.
5.Conservationof Electriccharge isa fundamental law
of nature.
6. Later there was developmentof law of
conservationof attributescalledbaryonnumber,
leptonnumberandsoon.
The lawsof nature do notchange withchange of
space and time.Thisisknownas symmetryof space
and time.Thisandsome othersymmetriesplaya
central role in modernphysics.Conservationlawsare
connectedtothis.