10 Short Notes E

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Physics Short Notes

BRAINS MOOZHIKKAL, CALICUT Short Notes 9048332443

Prepared y Fassal Peringolam

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ElectrolysisxThe conduction of electricity through an electrolyte

together with the resulting chemical changes.xIn electrolyte the electric current is due to the motion of

free ions.Application of chemical effect

x

To extract metals from their ores; to purify metals; forelectroplating; for anodisation.

ElectroplatingxElectroplating is the process of coating a metal on the

surface of a conductor by electrolysis.xWhich metal is to be used for electroplating, that metal is

Anode (positive electrode) and the solution of the samemetal is to be used as the electrolyte. The object which isto be electroplated is to be used as the cathode (negativeelectrode).

Usesof electroplatingxImprove the appearance, to prevent corrosion.

Law of ElectrolysisxThe mass of a substance liberated from an electrolyte or

deposited on the electrode is directly proportional to thecharge that is passed through the electrolyte.

x

mQ or m =a constant Q

Heating DevicesxHeating coil (Main part)xHeating coils are made of Nichromex

Characteristics of Nichrome: High melting point andresistance, ability to remain in red hot state for a long time

Joules LawxThe heat produced by an electric current flowing through

a conductor is equal to the product of the square ofcurrent passed, the resistance of the conductor and timefor which the current is passed.

x

Heat H = I2Rt or H = IVt or H =

or H = Pt


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xI=Current, R=Resistance, V=Voltage, t=Time, P=PowerPower

xPower is the rate at which work is done.

x

Power =Wk

Ti

xP = I2R or P = VI or P =

xUnit of Power: WattSafety fuse

xParts:Porcelain block, porcelain bridge, fuse wirexFuse wire:Alloy of tin and lead(Low melting point)x

Safety fuse is a mechanism to safe electrical appliances by

stopping huge current due to short circuit or overloadingin a circuit.

Incandescent lamp(Filament lamp)xMain partFilamentx

Filament is made of tungsten.xCharacteristics of tungsten: High melting point and

resistance, ability to remain white hot for a long time.xWorking:Heat is produced when current flows through

the tungsten filament and produces white light.xTungsten is the pure metal with maximum resistivity.

Discharge LampsxMain parts:Two electrodes, a glass tube filled with gasx

Working:As a result of the collision of ions and electronswith unionized particles and produces light.

xThe colour of light depends in gas(Neon-Orange; Nitrogen-Red; Sodium-Yellow; Mercury-White; Chlorine-green;

Hydrogen-Blue)Fluorescent Lamps

xWorking:The electrons ionize mercury atoms, ultravioletrays are produced. These rays are absorbed by thefluorescent materials and produce visible light.

xMerits: High longevity (five times that of filament lamp),Shadow minimized, Energy loss is less, Gives greaterintensity of light.

CF lamps


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xA CFL has a unit of electronic circuit and fluorescent tubecontaining mercury vapour.

LED Lampsx

A very low power is enough for LED lamps.

Electromagnetic InductionxThe magnetic flux associated with a coil changes by the

relative motion of the coil or magnet.

x

The phenomenon of producing an in a conductor as aresult of change in the magnetic flux linked with the

conductor is electromagnetic induction.xThe developed due to electromagnetic induction is

called induced and the current so obtained is calledinduced current.

xGenerator, moving coil microphone etc. work on theprinciple of electromagnetic induction.

Generators are two types.AC generator

x

Generator gives alternating current.xMain parts:

Field magnet: This is the magnet which producesmagnetic flux in a generator.

Armature: An armature is an arrangement of insulatedcopper wire wound on a soft iron core.

Slip rings: They are full rings fused to the ends of thearmature coil.

Brushes:An arrangement that is always in contact withthe slip rings

xWorking: When the armature rotates in the magneticfield, an alternating is induced in the coil. The currentis carried to the external circuit through the brusheskeeping contact with the slip rings.

xDifferent stages of the rotation of the armature: Duringthe first half of rotation the current begins from zero and

reaches the maximum positive value, then decreases


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gradually and comes to zero. In the second half, thecurrent reaches the maximum negative value, thendecreases gradually and reaches zero.

x

As a result of variation of the magnetic flux linked with aconductor, a current is induced in it, the direction ofwhich changes continuously. This is known as alternatingCurrent (AC).

DC generator

xDC Generator gives direct current.xField magnet, armature and split rings are main parts.xWorking: When the armature rotates in the magnetic

field, an alternating is induced in the coil. The flux cotin the first half of the rotation is in one direction and inthe opposite direction during-the second half rotation.Hence the direction of flow of current in the armaturechanges. When the direction of the current in thearmature changes during the successive half rotations,the contact of one half of the split ring shifts from onebrush to the other. So the-direction of the current in theexternal circuit does not change.

Similarities and dissimilarities of the structure ofan AC generator with a DC generator

xField magnet, armature and brushes are common in ACgenerator and DC generator.

xIn an AC generator the end points of the armature coil areconnected to slip rings but in DC generator the end points

of the armature coils are connected to split rings.

Moving coil microphonexIn moving coil microphone, the voice coil remains in the

magnetic gap of a powerful magnet. The voice coil vibrateswith the vibrations of the diaphragm when sound wavesfall on it. The movement of the voice coil across themagnetic field induces an electric current in the coil. The

intensity of the current varies in accordance with thevariations of sound waves falling on the diaphragm.


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xWhen the intensity of sound produced in front of thediaphragm increases; the amplitude of the inducedelectric signal formed in the coil also increases.

x

In moving coil microphone sound energy is converted intoelectrical energy

Mutual inductionxA magnetic field is generated around the primary solenoid

when an electric current is passed through it byconnecting the ends of the solenoid to a battery cell. But

induced is not produced in the secondary solenoid asthere is no change in this magnetic flux. When the switch

is on and off the flux linked with the secondary coilchanges and thus an is induced in the secondary coil.

x

Here AC is passed through the primary coil. The directionof ac changes at regular interval continuously. As thesecondary coil is located at this magnetic field whichchanges at regular interval continuously, the change in

flux causes the production of an induced in thesecondary coil continuously. So the bulb glows

continuously. If the number of turns of the secondary ismore than the number of turns of the primary the inducedemf increases and if the number of turns of the secondaryis less than the number of turns of the primary theinduced emf decreases.

xWhen there are two nearby coils the variation of currentin one of them produces a change in the magnetic flux

around it and an is induced in the secondary coil.

Transformer: Transformer are Two typesStep up transformer

xIncreases AC voltagex

Number of turns is less and thick wire is used in primaryxNumber of turns is large and thin wire is used in

secondaryxIn primary Current is large and Voltage less

Step down transformer

x

Decreases AC voltage


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xNumber of turns is large and thin wire is used in primaryxNumber of turns is less and thick wire is used in

secondaryx

In primary Current is less and Voltage large

=N

N ; VI = VSIS ;

=

N

N=

VS =Secondary voltage; VP=Primary voltage;NS=Secondary turns; NP=Primary turns;IS =Secondary current; IP=Primary current.

Self-Inductancex

It is the phenomenon of inducing emf in a coil caused bythe variation of magnetic flux produced by a varyingcurrent in the same coil.

xThe effective voltage is reduced through a conductor dueto back emf.

InductorsxInductors are coil which can oppose the changes of

current in a circuit.Flemings left hand rule

xStretch the thumb, fore finger and middle finger of the lefthand so that they are perpendicular to one another. Thefore finger represents the direction of the magnetic field,the middle finger represents the direction of the current,and the thumb indicates the direction of the force, This isFlemings left hand rule.

Motor PrinciplexA current carrying conductor in a magnetic field

experiences a force. Electric motor, moving coil loudspeaker etc. work on the principle of electric motor.x

Electric motor(electrical energy to mechanical energy) andLoud speaker (electrical energy to sound energy) works onthe motor principle

Electric Motorx

It has a field magnet and an armature capable for freerotation about an axis. The armature rotates in the

magnetic field produced by the field magnet. When a


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current flows through the armature, it moves on the basisof Flemings left hand rule.

Moving coil loudspeakerx

A voice coil placed between the poles of a permanentmagnet is the important part of a loud speaker. Adiaphragm is attached to this coil.

xThe electrical signal corresponding to the variations ofsound from the microphone is amplified by an amplifierand is fed to the voice coil. The voice coil vibrates inaccordance with the intensities of the electrical signals.

These vibrations induce vibrations on the paper cone

attached to the coil causing vibrations to the air around it.As a result, the original sound is reproduced more loudly.

xMainly three types of power stationHydroelectric power station

xHydroelectric power stations are power stations whereelectricity is produced by rotating turbines of a generatorby allowing water stored at a height to flow through pipes

or tunnels.xMechanical energy Electrical energyxEg: Moolamattam,Pallivasal,Kuttiadi,Sabarigiri

Thermal Power stationxIn thermal power station the heat energy released during

the burning of fuels like naphtha, coal and lignite is usedfor heating water and producing steam at high pressure.

The steam thus produced is used for rotating turbines and

generate electricityxChemical EnergyThermal Energy Mechanical

EnergyElectrical EnergyxEg: Kayamkulam, Neyveli, Ramagundam, Brahmapuram.

Nuclear Power Energyx

In nuclear power station the heat energy released duringnuclear fission is used for heating water and producingsteam at high pressure. The steam thus produced is used

for rotating turbines and generate electricity


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xNuclear EnergyThermal Energy MechanicalEnergyElectrical Energy

xEg: Kalpakkam,Tharapur,Kotta,Narora.

Power GeneratorxMainly Three Parts.xRotor : The rotating part (Field magnet)xStator : Stationary part (Armature)xExcitor : (Auxiliary Generator) : Providing DC to

electromagnets in large AC generators)xThe problems when a permanent magnet is used as the

field magnet.

The limitation of producing strong magnets.The magnetic strength of permanent magnet losesgradually. So the flex cannot be maintained stable.The strength ofthe field magnet cannot be increases ordecreases.

xThe armature of a power generator will be heavy and so itis used as the stator. This helps to eliminate the graphitebrush and avoid sparks.

Single phase Generatorx

One Field magnet and One Armature CoilxOnly a single Ac is obtainedx

It is used in House and ShopsThree Phase Generator

xOne Field magnet and Three Armature CoilxThree distinct AC is obtainedxIt is used in Power station

x

Numbers of turns are equal in three armature coil.xThree identical armature coil at angle of 1200 with one

anotherPower Transmission

xThe process of sending electricity through wire from thegenerating station to the area where it is consumed.

xIn our country electricity is generated in 11 kV.xStep up transformers are used at the substation near the

powerhouse.


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xIn other stages of distribution step-down transformer isused.

xProblems related to the Transmission(Transmission loss):x

Voltage drop and energy lossTransmission loss minimized

xBy raising the voltage during transmissionxBy reducing strength of electric currentxUse low resistance material.

Star ConnectionxIt is a mechanism to send electricity from distribution

transformer to house

x

4 lines(3 phase +One neutral)xThree phase line are connected to a point is called neutral.x

The line starting from this point is neutral line.xThe voltage of this line is zero.xPotential difference between Two phase line is 400VxPotential difference between phase line and neutral line is

230VxPotential difference between neutral line and earth is 0V

x

Potential difference between phase line and earth is 230VHousehold wiring

xPhase line and neutral linex

The different electrical appliances that are usually used inour houses works at 230V.

xBulbs connected in parallel circuit are brighter.xIn parallel circuits, it one bulb stops working, then all

other bulbs keep working normally. But in series circuit it

one bulb stops working, then all other bulbs also stopworking.

Advantages of parallel circuits in domestic wiringare

xIn parallel circuits, if one electrical appliance stopsworking then all other appliances keep working normally.

xEach appliance has its own switch due to which it can beturned on or off independently, without affecting other

appliances.


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xEach appliance gets the same voltage.xThe overall resistance of the circuit is reduced due to

which the current from the power supply is highx

Connect in parallel of the order Watt Hour meter mainfusemain switch fusesswitches appliances

xFuse is connected to the phase line.xThe switches are connected to the phase linexIn house all appliances are connected in parallel to neutral

line through switchesThree pin plug and two pin plug

xThe line that comes in contact with pin E is the earth line.

It is thicker and longer than the other two. This line isconnected to the metallic covering of the appliance.

x

The phase and neutral lines are connected to the heatingcoil of the electric iron.

xWhen the phase line comes in contact with the outermetallic case the current will flow to the earth.

xIn our house watt hour meter is the device which connectsthe electric lines first. Watt-hour meter is an instrument

which can he directly read the amount of electrical energy;consumed. It is connected at the beginning of the electriccircuit.

Measurement of electrical energyxThe quantity of energy consumed in one hour at the rate

of 1j/s is called Kilowatt hour. It is the commercial unit ofelectricity.

SoundxSound is a form of energy which makes us hear.xSound is produced by the vibration of objects(solid, liquid,

gas)Source of Sound

xDevices that produce sounds are called source of sound.Sources of sound The part that vibrates

Drum, Tabala Diphragm

Violin, Veena, Guitar StringsFlute Air


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Natural frequencyxEvery vibrating object has its own frequency. This is its

natural frequency.

Factors depends on vibration (frequency of a wire)xThe nature of materialxThickness of wirexLength of wirexTension of the wire

Transmission of soundxSound needs a material medium to travel.xAstronauts in space or on the moon use radios to talk each

other because there is no air on the moon to carry thesound waves.

Medium Velocity (m/s)Aluminium 6420Steel 5950Pure water 1498Air 340

xThe sound waves are longitudinal waves.Measures of Wave

Wavelength()x

The distances between two nearest points in a wave are insame phase of vibration.

xUnit-metre(m)Frequency(f)

xThe number of vibration per second.xUnit-Hertz(Hz)

Velocity (v)x

It is the distance travelled by a wave in one second.

xUnit-(m/s)Relation between , fand v

x

v = f or f=v/ or =v/fCharacteristics of Sound

IntensityxThe intensity of the sound is the amount of energy passing

through unit area per second perpendicular to thedirection of propagations.


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xThe intensity of sound is proportional to the square of theamplitude of the sound.

xIts unit is W/m2

LoudnessxLoudness is the measure of audibility produced by sound

in u person.xLoudness depends on the intensity, frequency and

efficiency of the ear.xThe unit of Loudness is decibel (dB).xSounds higher than 120 dB are painful to the ear.

Pitch

x

Shrillness of a sound felt by the ear is its pitch.xThe faster the vibration of the source, the higher is the

frequency and higher is the pitch.Two Types

xSounds of high pitch: Chirping of crickets, whistles, soundof women, sound of children

xSounds of low pitch: Thundering sound, sound of man,sound of cow, sound of drum

Timbrex

The quality of sound (timbre) that distinguishes thesounds of two persons.

Bass and TreblexA group of sound waves of low pitch is bass. A group of

sound waves of high pitch is treble.Doppler Effect

xThe change in frequency experienced by the receiver either

because of the relative motion of the source or the receiveror both is Doppler Effect.

xWe felt that there is an increase in frequency of thewhistling from a fast train when it comes from a distanceto the station and a decrease in frequency when the trainpasses us without stopping. It is due to Doppler Effect.

Natural vibrationxThe free vibration of an object is called Natural vibration.

x

Free vibration depends on shape and elasticity etc.


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xIf an object is allowed to vibrate freely, the object shouldvibrate in its own natural frequency.

xThe frequency of the natural vibration is called natural

frequency.Forced vibration

xIf a vibrating body forces another body to vibrate with thesame frequency as that of the vibrating body, it is calledforced vibration.

ResonancexThe wooden part of the veena and sonometer is almost

alike. When an excited tuning fork mounted on a

sonometer, between the bridges when the distancebetween the bridges became a particular length, thebridges is forced to vibrate at a frequency of tuning fork.Due to resonance the wire may start vibrating violentlyand the paper rider thrown away from the wire.

xIf the natural frequency of a body undergoing forcedvibration is the same as that of the forcing body, then theyare said to be in resonance.

x

The body undergoing forced vibration will vibrate withgreater amplitude.

xSonometer and Resonance column are used in laboratoryfor explain resonance.

Practical effects of resonance

xSoldiers cannot march through a hanging bridgexThe doors and windows of nearby buildings vibrate at the

time of firework.

x

When we talk near instruments of violin, guitar etc. itsstring vibrates.

Beats

xIf two sound sources of slightly different frequencies aresounded together, a periodic rise and fall in intensity willbe heard. This is known as phenomenon of beats.

Persistence of Hearing

x

The sensation of hearing produced by sound is retained

for a period of 1/10 second. This peculiarity of the ear ispersistence of hearing.


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Limit of audibilityxNormally a person can hear frequencies from 20 hertz to

20,000 hertz. This is limit of audibility.x

Sounds of frequency less than 20 Hz are infrasonic soundsand sounds of frequency greater than 20 kHz areultrasonic sounds.

Uses of ultrasonic soundsxTo record the functioning of the heart (Echocardiography)xTo study the functioning of internal organs like liver,

kidney, uterus (Ultrasonography)xTo crush small stones formed in the kidney

x

To measure the depth of oceans (SONAR- SoundNavigation and Ranging)

Situations/Animals to utilize Infra sonic soundsxElephants, whales, Rhinoceroses, earthquakes.

ReflectionxSound bounce back when it falls on hard surface is

reflectionxMegaphones, Horns, Stethoscope, Sound board are

utilizing multiple reflections.Echo

xEcho is the same sound heard a gain after sound is heard.x

The distance from the sound reflecting surface to hear anecho should be above 17m

ReverberationxThe persistence of sound as a result of multiple reflection

is reverberation

Acoustics of buildingsxAcoustics of buildings is the branch of science which deals

with the conditions to be fulfilled in the construction of ahall for clear audibility.

ProblemsxCannot hear sound properlyxThe sound is heard repeatedlyxThe sweetness of music is lost

x

Loudness is insufficient


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Minimize OptionsxA large number of ventilators and windows are providexCurtains having many folds are usedx

Carpets are usedxWalls are made rough.xSound Pollution:

Ways to minimise sound pollutionxPlant trees on the roadside.xObey the laws to control noise pollutionxMaintaining automobiles in good condition

Dispersion of LightxThe phenomenon of splitting of visible light into its

constituent colours is dispersion.x

The component colours in the white light deviate atdifferent rates according to their wavelength; this is thereason for dispersion.

RainbowxThe dispersion of light in water forms rainbow.x

The light ray entering to a drop of water undergoes tworefraction and one total internal reflection.

xThe line joining the centre of the rainbow and the observeris the line of vision.

xRainbow is seen as an arc because each colour makes adefinite angle with the line of vision.

Opaque objectsxAn opaque object reflects only its colour. It absorb all other

colours falls on it.Transparent objects

xThe colour of a transparent object depends upon thecolour that it allows to pass through it.

Persistence of visionxThe sensation of seeing an object remains for about 1/16

of a second after the object is removed from view. This is

known as persistence of visionNewtons colourdisc


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xWhen the Newtons colour disc was rotated at high speedit appeared white. Due to the persistence of vision we feelthe effect of seeing all colours together.

Primary coloursxGreen, red and blue are called primary colours.xThree colours green, red and blue super impose appears

white.xPrimary colours cannot be obtained by mixing other

colours.Secondary colours

xThe colours formed by the combination of any two primary

colours are secondary colours.Complementary colours

x

The pair of colours combined with a primary colour to getwhite light is called complementary colours.

colourssecondary

colourPrimarycolour

complementarycolour

Green+red yellow green Magenta

Green+blue cyan red cyan

Blue+red Magenta blue yellowScattering of light

xWhen light falls on rough surface or on tiny particles inthe atmosphere, it reflects into all directions. Thisphenomenon of light is known as scattering

x

Red colour, which has a long wavelength, can travel largedistances without scattering.

The rising or setting sun and the colour of the sky

x

The colour of longer wavelength red in the sun raysreaching the earth from the rising or setting sun. So thesun in red during sunrise and sunset.

xColours of shorter wavelength such as violet, indigo andblue scatter more when compared to other colours oflonger wavelength, and spread in the sky.

xThere is no atmosphere in the moon. So light reach at themoon is not scattered. There is no presence of any kind of

scattered light, in the moon, sky appears dark.


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Ultraviolet rays and infrared rays

xAn infrared ray which has more wavelength than visiblelight and ultraviolet rays of least wavelength are the

radiations on either side of the visible light.xInfrared rays travel long distance with less scattering.xThough ultraviolet radiations are invisible; we can detect

its presence through its reactions on photographic plate.xUltraviolet radiations of moderate intensity helps to

produce vitamin D when react with, the coloured; pigmentmelanin present below our skin

xSubstances which absorb light of shorter wavelength and

convert them to light of larger wavelength are fluorescentsubstances.xWhen ultraviolet radiation fall on fluorescent substances,

their wavelength increasesxFluorescent paints are able to absorb ultraviolet

radiations and convert into visible light.

Components in an electronic circuit

ResistorsxThe function of a resistor is to supply the necessary

potential difference to the components by regulating thecurrent in a circuit. Resistance is measured in the unitohm. Its symbol is . The value of resistance is recordeddirectly on it or using a colour code.

Inductors

xInductors are coils of conducting wire which can resist

variations of electric current in a circuit. The ability toresist the variation of electric current is inductance. Theunit of inductance is henry.

Capacitors

xCapacitors are components used to store electric chargesand release them when necessary. A capacitor isconstructed by placing a dielectric between two parallelmetal plates. The unit of capacitance is farad (F).

x

Capacitors are commonly known by the dielectric used inthem.


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xCapacitors which use an electrolyte as a dielectric areelectrolytic capacitors.

Semiconductors

xThere are substances with properties different from bothconductors and insulators. They are semiconductors. Thetwo main semiconductors are Germanium and Silicon.Change the conductivity of semiconductors by addingother elements.

Diode

xOne end of a diode is marked positive and the other end,negative.

xWhen p - end of a diode is connected to positive pole andn - end to the negative pole of a cell, then a current ispassed through the diode.

x When a diode is connected in a circuit so that currentflows through it, the diode is said to be forward biased andwhen no current flows, the diode is said to be reversebiased

Light emitting diode (LED)

x

Light emitting from certain diodes when electric currentpasses through them. They are called LED.Rectification

xDiode converts AC into DC. This is rectification. A devicewhich makes this possible is a rectifier.

xDuring the positive half cycle of the input voltage there isoutput voltage but during the negative half cycle of theinput voltage there is no output voltage. This type rectifieris called half wave rectifier.

Full wave rectifierx A full wave rectifier is one which is arranged to allow the

AC to flow continuously in one direction through it.Transistor

xA transistor is an electronic component made ofsemiconductors. They have three terminals.

Amplificationx

Amplification is the process of increasing the strength ofelectrical signals.


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xThere is no difference in the number of cycles formed in afixed time interval before and after the amplification. Theamplitude of the wave increases

Integrated circuitsxThe device Integrated circuit or IC is a small

semiconductor chip with lakhs of electronic componentslike resistor, capacitor, diode and transistor suitablylinked in them.

xThe processor which can be called the brain of thecomputer is an integrated circuit.

x

The moon takes approximately 27 days to revolve, roundthe earth once.

xThe moons orbit can be divided into 27 segments, each

of 131

3degrees.

Asterism (Naal)

x

The time taken by the moon to describe 1/27 of its orbitis called an asterism or a birthstar (naal).

xAsterisms are formed on the basis of the stars that comein the moon's orbit.

x365 days are required for the earth to revolve oncearound the sun.

Ecliptic

xOur feeling of the sun moving among the stars is due tothe revolution of the earth.

xThe orbit, along which the sun appears to move among the

stars, is known as ecliptic.ConstellationsxThe ecliptic is divided into 12 equal parts.x

These are the 12 solar constellations.xEach constellation is known by the shape of the stellar

distribution in it.xA Malayalam month will be known by the name of the

constellation in which the sun appears to be at that time.

x

The sun passes through the 27 asterisms also while itpasses through the 12 constellations.


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xThe sun takes nearly 365 days to pass past 27 asterismsonce.

Njattuvelax

The period of time for which the sun appears together withan asterism is a njattuvela.

xA njattuvela is approximately 13-14 days.The Sun

xThe sun, which is the centre of the solar system is one staramong them

xThe sun is a white hot gaseous sphere.Photosphere

x

The outer layer of the sun that we can see is called thephotosphere.

x

The source of the sun's energy is the fusion of hydrogentaking place in the core.

ChromospherexThe chromosphere which is the thin layer outside the

photosphere.Corona

x

The corona which is an extensive region outside it can beconsidered as the atmosphere of the sun.

Sun spotsx

Though the temperature of the photosphere comes to 6000kelvin, there are certain regions of lower temperature(about 3500 kelvin) in it that appear as black spots. Theseare known as sun spots.

Solar wind

x

From the surface of the sun, there is a massive flow ofhelium nuclei (alpha particles) and hydrogen nuclei(protons). This is the solar wind

Solar prominencesxSometimes huge flames rise from the surface of the sun

and fall back in the form of an arch. They are the solarprominences.

xThere a relation between the colours and temperatures of

the stars.


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Nebula

xThe gaseous cloud in the interstellar space is the birthplace of stars. These are known as nebula.

xThe contraction of the gaseous cloud in the nebula due togravitation, initiates the birth of a star.

xA star becomes visible to us only when the energy due tofusion is produced.

Path of evolution of the sun

x

Nebula Primitive star Main sequence star Redgiant White dwarf Black dwarf

Galaxy

xA galaxy is a cluster of billions of stars and interstellarmatter, bound by gravitational force.

xThere are billions of galaxies in the universexMilky Way is our galaxy.xIt takes 8 minutes for the light from the sun to reach the

earth.Astronomical Unit

x

The distance between the sun and earth.Light Year

x

The distance travelled by light in one year.x

Dr. Vikram Sarabai (1919 - 1997), is the the father ofIndian Space Research.

xIndian scientists have been able to develop many artificialsatellites and launching vehicles like GSLV(Geosynchronous Satellite Launching Vehicle) to launchgeostationary satellites, PSLV (Polar Satellite LaunchVehicles) to launch polar satellites etc.

Equatorial satellites (Geostationary satellites)xEquatorial satellites revolve around the earth along an

orbit above the equator. If their period of revolution is thesame us the period of the rotation of the earth, they arecalled geostationary satellites.

Polar satellitesxThe satellites revolving along an orbit passing above the

north and south poles of the earth at an altitude of 200-1000 km are called polar satellites.


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Combustion/Burning

xBurning is the process in which heat and light are formed

by the intense reaction of substances with oxygen.Fuels

xFuels are substances to produces heat energy.Substances formed when fuels burn

x

Carbon dioxide; Charcoal ; Water vapour; Carbonmonoxide (CO)

Conditions for the complete combustion

xDryness

x

Adequate supply of oxygen.x

Facilities for the removal of gases produced as a result ofcombustion.

Partial burning

x

In the absence of sufficient quantity of oxygen, carbonmonoxide is formed in a greater measure, carbon dioxideand smoke in a small measure. This kind of burning ispartial burning.

Drawbacks of partial combustionxFuel lossx

Wastage of timexLarge scale environmental pollution.x

Large quantity of smoke is produced.xIncrease the amount of C and CO.

Source of fuels

x

Diesel, LPG Petroleumx

Petrol, Naphtha PetroleumxCNG Natural gas

x

Coal Coalx

Hydrogen WaterxKerosene PetroleumxFire wood Trees

xElectricity Power stations, water, fossil fuelsFossil fuels

xFossil fuels ate formed by the transformation of animalsand plants buried in the earth millions of years ago, in theabsence of air, at high temperature and pressure.

x

Coal, petroleum and natural gas are fossil fuels.x

They are non-renewable sources of energy.


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Physics Short Notes



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CoalxBased on the carbon content it is classified into four

groups as peat, lignite, anthracite and bituminous coal.

Situations where Coal are usedxIt is used as household fuel.xIt is used as industrial fuel.x

It is used as the fuel in thermal power stations.xIt is used to produce Coaltar, Coal gas Coke and Ammonia.xMore details of CNG, LNG and LPG as fuels:

CNG

LNG

LPG

It cannot be liquefied at

normal pressure.It is difficult to transportto far off places.Methane is the maincomponent

It can be liquefied

at normalpressureEasy to transportMethane is themain component

It can be liquefied

at normalpressure.Easy to transportMain componentsare propane andButane

Calorific valuexThe amount of heat liberates by the complete combustion

of 1 kg of fuel is its calorific value.

x

Its unit is joule/kilogram.xHydrogen is the fuel which has the highest calorific value.xHydrogen is used as a fuel in rockets

BiomassxBiowastes are generally known as biomass.

Properties must a substance have in order to beconsidered as a good fuel are

xIncreased availability; low cost; minimum atmospheric

pollution; a liquid fuel must not evaporate quickly atordinary temperatures; low ignition temperature; easy tostore and transport.

The problems that arise due to their combustion are

xSmoke is produced; Carbon monoxide is formed ; Gaseslike sulphur dioxide are formed

Solar devicesxSolar Panel; Solar water heater; Solar cooker; Solar

thermal power plant.


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