Physics Study Notes Igcse Edexcel

8/17/2019 Physics Study Notes Igcse Edexcel

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PHYSICS STUDY NOTES IGCSE EDEXCEL;

SECTION A: Forces and motions

Speed = distance/ time

Instantaneous speed is the speed of an object from one instant to the other as theaccelerator or brake is used. Displacement is the distance travelled in a particular

direction from a specic point.

Velocity is the rate of motion per unit time. It is how fast the object is travellin with

a direction.

Velocity = displacement/time taken

!cceleration is the rate at which objects chane their velocities.

!cceleration = "nal velocity # initial velocity$/ time taken

%orces are vector &uantities. 'here is friction( weiht of object) reaction force by the

*arth and the force of object i.e. push. 'here are many forces such as air resistance(

up thrust( manetic( electrostatic and nucleus. If you apply a force to an elastic

band it chanes shape. It will stretch if put under tension and would shorten if

compressed.

Sprins chane shape when a force is applied to them and return back to oriinal as

soon as the force has been removed. +ooke,s law states that the e-tension of sprin

is directly proportional to the force applied. 'he elastic limit is when the sprin

starts to stretch more for each successive increase in the load force. nce it has

passed this limit the sprin has chaned shape permanently and will not return to

its oriinal lenth.

'he acceleration of an object is aected by both its mass and the force applied to it.

%orce = mass - acceleration

'he stoppin time is the sum of thinkin distance and brakin distance. 0eaction

time could be aected by the ae of the driver( if the driver is tired( if the driver is

under alcohol or drus. It could also be due to poor eyesiht. 1reakin distance

could be aected by the mass of the vehicle( the speed the vehicle is oin on( road

conditions and conditions of the tyres. 'he bier the mass of the car the loner thebrakin distance.

2eiht = mass - ravitational pull.

bjects fallin e-perience two forces) weiht force by ravity and the opposin dra

force.


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Staes of air resistance and acceleration) air resistance is very small but starts to

increase. 'he air resistance increases. 'hey are the same 3terminal velocity4 and

therefore have a balanced amount of acceleration and resistance. 'he lare air

resistance starts to decelerate. !ir resistance decreases until they are the same as

weiht and therefore reach another terminal velocity. n the round( the weiht is

e&ual to the upward force.

5omentum is a measure of how di6cult it is to stop somethin that is movin. It is

a vector &uantity.

5omentum = mass - velocity. It is measure in km/s.

%orce = chane in momentum/ time taken

5omentum will remain constant as lon as there is no interference and the system

is isolated.

5omentum before = momentum after

57V7 8 59V9 = 5:V:

Impulse is the chane in momentum

%orce - time = chane in momentum

If you increase the time( you decrease the force on the object. ;ars are desined

with various safety features that increase the time over which he car,s momentum

chanes in an accident. 'hese include seat belts( crumple


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>? derees and a perpendicular is the force that will have the best eect on the

door.

Sum of anticlockwise = sum of clockwise

;ounter balance is the thin needed to balance out a lon part of a pivot. 'he

centre of ravity is if you support the object at this point there is no turnin

moment. It is also called the centre of mass. In a symmetrical card the centre of

ravity will be located where the a-es meet. ! stable object is one that is di6cult to

push over.

'he *arth is one of the @ planets that orbit the sun. 'he orbits of planets are

elliptical with the sun close to the centre.

'he further the planet is away from the sun( the loner it takes for the planet to

orbit the sun once. 'he closer the planet is from the sun( the hotter the surfacetemperature of the planet.

'he strenth of ravity on a planet or moon is called its ravitational eld strenth.

Alanets are held in orbit by the ravitational pull of the sun.

5oons are natural objects that orbit a planet. 5oons are nonBluminous objects. 2e

see them because they reCect liht from the sun.

;omets orbit the sun. 'hey are appro-. 7B:? km in diameter and are made of dust

and ice. 'heir orbits are very elonated. !s a comet et closer to the sun( the

ravitational forces actin upon it increase and it speeds up. !s the opposite end ofits orbit( the ravitational forces are much smaller and the comet therefore travels

much slower.

!steroids are minor planets or rocks that orbit the sun. 'hey vary in si


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eostationary is the orbital period of a communication satellite which is 9E hours so

that it remains above the same part of the *arth,s surface. It can,t be interrupted or

damae.

SECTION : E!ectricit"

0in circuits consist of) the live wire which provides the path alon which the

electrical enery from the power station travels. It has an alternatin current

between neative and positive. 'he neutral wire completes the circuit. 'he *arth

wire usually has no current Cowin throuh it. It is there to protect you if an

appliance develops a fault.

'he outer part of a plu is called a casin and is made out of plastic. Alastic is a

ood insulator. ;onnections to the circuits are made out of three brass pins as brass

is an e-cellent conductor of electricity.

5any plus contain a fuse. 'he fuse is usually in the form of a cylinder or cartride

which contains as a thin piece of metal that has a low meltin point. If the current

ets too hih( then the metal melts( the circuit breaks and the current stops Cowin.

! fuse si


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2hen the switch is connected to the neutral wire then the electricity can still Cow

throuh the appliance and the user could still et shocked. +owever while it is

connected to the live wire then the person cannot et shocked.

Aower = current - voltae. Aower is measured in watts( current is measured in amps

and voltae is measured in volts.

*nery = power - time. *nery is measured in joules( power is measured watts and

time is measured in seconds.

!lternatin current is when current Cows in two ways( whereas direct current is only

in one way.

;hare 0elative mass 2here it is foundArotons 87 positive 7 In the nucleuseutrons ? neutral 7 In the nucleus*lectrons B7 neative 7/7@>> ut of the

nucleus

!toms normally have an e&ual amount of protons compared to the amount of

electrons( but if it is not it is either a positive or neative ion. If an unchared plastic

rod is rubbed with an unchared cloth( it is possible for them to become chared by

friction. 'he rod becomes positive and the cloth becomes neative. 'he rubbin

action doesn,t create or produce a chare but instead separates the chares as it

transfers the electrons from one of the objects to the other

If the chares are the same( they repel. If the chares are opposite( they attract.

2hen a chared object meets an unchared object( the positive or neative chares

are attracted to the opposite chare and repel chares that are the same

backwards.

'he old leaf electroscope) the electroscope is unchared. 'he rod is positively

chared. 'he electrons are attracted to the rod and move upwards. 'he bottom now

has more protons than electrons. 'he protons on the bottom and in the old leaf

repel and the old moves further. 2hen you put your ner on it( electrons from the

electroscope o to the round( makin the electroscope have a balance of electrons

and protons at the bottom. 2hen you put the positively chared rod aain( the

electrons move upwards and there is less repulsion so the old oes downwards.*arthin is when electrons are released down to *arth.

*lectrostatic paint sprayin) as the droplets emere from the spray un( they are

chared. !s the droplets all carry the same chare they repel and spread out

formin a ne spray. 'he metal bicycle frame has a wire attached to an electrical

supply ivin the frame the opposite chare. 'he paint droplets are therefore

attracted to the surface of the frame. 'here is the added benet that paint is


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attracted into places( such as tiht corners( that miht otherwise not receive such

as ood coatin.

5any modern printers use inkjets to direct a ne jet of ink drops onto paper. *ach

spot of ink is iven a chare so that as it falls between a pair of deCectin plates(

electrostatic forces direct it to the correct position. 'he chares on the plateschane hundreds of times each second so that each drop falls in a dierent position(

formin pictures and words on the paper as re&uired.

Ahotocopiers) the drum is chares with a positive chare) Imae of object to be

copied is formed here. ;hare stays only where imae is dark. 'oner drops on to

drum and sticks to chared areas. Surplus toner is removed. Aaper is pressed

aainst toner imae to ive imae on paper. Aaper is heated to melt toner imae.

'his forms permanent imae on paper.

*lectrostatic precipitators) as the smoke initially rises in the chimney( it passes

throuh a mesh of wires that are hihly chared. !s they pass throuh the mesh(

the ash and dust particles become neatively chares. +iher up the chimney these

chared particles are attracted by and stick to lare( metal earthed plates.

Aroblems with static electricity) as aircrafts Cy throuh the air( they can become

chared with static electricity and the hue dierence in potential causes the

chares to escape to the earth durin refuelin which can easily cause an e-plosion.

'his can be solved earthin the plane as soon as it lands. 'elevisions screens and

monitors become chared with static electricity as they are used. 'hese chares

attract liht unchared particles such as dust. ur clothin( under certain

circumstances( becomes chared with static electricity. 2hen we remove the

clothes there is the possibility of receivin a small electric shock as the charesescape to *arth.

;onductors allow electrons to Cow easily throuh them. 2hereas( insulators don,t

allow electrons to Cow easily. ;onductors could be metals and insulators could be

plastic.

2e measure the si


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past. 'he component with a hiher resistance will have a hiher voltae. 'he

component with a hiher resistance will have a lower current.

!ll

components in a circuit oer some resistance to the Cow of chare. Some allow

chares to pass throuh very easily losin very little of their enery i.e. connectin

wires. 'hey have low resistance. 'he Cow of current throuh some components is

not so easy and a sinicant amount of enery is used to move the chares throuhthem. 'his enery is converted into other forms( usually heat. ;omponents like this

one have a hih resistance.

2e measure the resistance of a component by comparin the si


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%i-ed resistors are included in circuits to control the si


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2avelenth is the distance between similar points from one to the other. 'rouh to

trouh or crest to crest.

'he number of waves produced each second by a source( or the number passin a

particular point each second is called the fre&uency. It is measured in hert


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waves are emitted by a transmitter. !s they cross an aerial( they are detected and

the information they carry can be received. Gses include radios and 'V,s.

Special electric circuits produce microwaves which are uided into rotatin

reCectors that send the microwaves in all directions. 'he microwaves are reCected

in all directions until they hit the food( where they are absorbed so the food etshotter. 'hey are used for communications as they pass throuh the *arth,s

atmosphere easily and are used to carry sinals to orbitin satellites. . 'he hotter an

object is the more enery it will emit as infraBred. Special waves can be used to

create imaes especially in the absence of visible liht. 'hey could be used to track

criminals. 'hey are used in remotes and can only work over short distances.

Visible liht is the part of the electromanetic spectrum that is visible to the human

eye. It is used for readin compact discs( communications and lookin inside the

body of patients. 'hey include colors such as red( orane( yellow( reen( blue(

purple and indio.

GV liht causes tan( but overe-posure will lead to sunburn and skin cancer and

blindness. 'hese can be protected by skin cream or protective oles. It is used in

Cuorescent tubes are GV tannin lamps.

HBrays pass easily throuh soft body tissue but it can,t pass throuh bones. !s a

result it can be used to check people,s bones. *-posure to too much HBray can

cause cancer. 'hey have to stand behind lead screens or to wear protective

clothin. amma rays are hih penetratin waves which cause damae to livin

cells such as mutations that lead to cancer at very small doses( however at lare

does it can be stron enouh to kill cancer cells completely.

'o send a messae usin a diital sinal( the information is converted into a

se&uence of numbers called a binary code. 'hese numbers are then converted into

a series of electrical pulses sent down the telephone lines.

! sinal that is converted into electrical voltaes or currents that vary continuously

is called an analoue( whereas a sinal that is converted into binary code is called a

diital sinal. Diital sinals are easy to reenerate whilst analoue sinals aren,t

and can be easily distorted.

bjects that emit their own liht are called luminous. 2hen the emitted liht enters

our eyes we can see the object. 5ost objects are nonBluminous and don,t emit liht.

2e see these nonBluminous objects because of the liht they reCect. Fiht waves

are transverse waves which can be reCected( refracted or diracted. 2hen a ray of

liht strikes a plane mirror( it is reCected so that the anle of incidence is e&ual to

the anle of reCection.

5irrors are often used to chane the direction of a ray of liht. It is used in

periscopes.


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Aroperties of an imae in a plane mirror) the imae is as far behind as the object in

front( the imae is the same si


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2hen white liht passes throuh a prism( it emeres as a band of colors called a

spectrum. 'he spectrum is formed because white liht is a mi-ture of colors and

each color travels throuh the prism at a slihtly dierent speed so each color is

refracted at a dierent anle. Since the prism has a dierent refractive inde- for

each color( each color emeres at dierent speeds and dierent anles.

!s the speaker cone moves to the riht( it pushed air molecules closer toether(

creatin compression. 'hese particles then push aainst neihborin particles so

the compression appears to be movin. 1ehind the compression there is an area

where all of the particles spread out. 'his is called rarefaction. 2hen this is

repeated many times( a lonitudinal wave is formed.

2hen the waves hit the ear( they strike the ear drum and make it vibrate. 'hese

vibrations are chaned into electrical sinals( which are detected by the brain.

Sound waves can travel throuh) solidsJ this is why we can hear people in dierent

rooms. Fi&uidsJ this is why underwater animals can communicate. asesJ this is why

humans can talk to each other.

Sound waves can,t travel throuh a vacuum because there are no particles for the

vibrations to be carried. 'he speed of sound depends on the temperature and

pressure of the medium. Kou can measure the speed of sound by usin echoes. Kou

stand is a sinicant distance from a wall and then multiply the distance by 9 and

divide it by the time.

Kou can measure the speed of sound by usin a resonance tube lled with water

until:/E of the wavelenth. ! sound of a known fre&uency would be made by a

tunin fork. 'he resonance will be heard when the lenth of the air in the tube is

e&ual to a &uarter of the wavelenth.

Speed of sound = fre&uency - wavelenth

Set the sinal enerator to ive a fre&uency of 7 k+


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Increasin the pitch increases the fre&uency of the waves. It makes the waves look

closer toether. %rom each compression to the other is the wavelenth and time.

Kou can nd the fre&uency of sound by usin a ;0. If you nd the time period then

divide by 7.

Gltra sounds are sounds that vibrate so &uickly( humans can,t hear them. +ih

fre&uency.

Infra sounds are sounds that vibrate so slowly( humans can,t hear them. Fow

fre&uency.

SECTION D: Ener%" Trans&ers

%or enery to be useful( we need to be able to transfer from one place to another

and to be able to convert it into whatever form we re&uire.

2hen you eat( you intake chemical enery. It is then burnt to enerate thermal

enery and to keep us warm. ur muscles convert the chemical enery into kinetic

enery. 'he movement enery could be used to make us speak.

*-amples of enery) liht( heat( sound( kinetic( electric( chemical( ravitational(

elastic and nuclear. 'he last E are all potential enery.

%or enery to be useful( we need to be able to transfer it from one place to another.

+owever there is always enery lost. It is called Lwasted, enery. *-amples includewhen the heater in a home converts electrical enery into heat enery( some of the

heat from the water is transferred from the water and onto the tank. !nother

e-ample is in a car( lots of the enery is converted into heat( sound and enery to

overcome the friction outside the car.

!n e-ample of enery conversions is when a cyclist eats food. 'he chemical enery

is converted into movement enery. 'he movement enery makes the wheels on

the bike to start movin. 'he movement of the wheel makes a enerator convert

the kinetic enery into electrical enery which turns on the lamp.

*nery is not created nor destroyed) it is just converted into dierent types.Ahysicists believe that the amount of enery in the universe is constant.

*nery transfer diarams show the enery input( the enery conversion process

and the enery output.


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Sankey diarams are a simpler and clearer way of showin what the input enery is

converted into. 'he width of each arrow is proportional to the amount of enery

involved.

*6ciency of a system is how much of the input enery is converted into enery that

you want.

Gseful enery output/ total enery output - 7??

*6ciency is a ratio and doesn,t have a measurement.

'here is a temperature called absolute


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moves into its place. ! ;onvection current is set up. 'he heater eventually heats up

the whole room.

'emperature is the sum of kinetic enery of all the particles in an object.

Since conduction is the main way heat can escape by( we have to know where

conduction occurs. ;onduction occurs in the walls( windows and the roof.

2ays to reduce heat loss in a house) loft insulation which is to put an insulatin

material in between the walls. ;avity wall insulation which is to put an insulatin

material in between the walls. %loor insulation which is the use of carpets( curtains

and more. Double la


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9N and the O* is PN. 0iht before the object hits the round( it has ?N A* and

7??N O*. 'his is all done with the assumption that friction isn,t taken into

consideration.

Oinetic enery of a movin object is calculated usin the formulaJ

O* = 7/95VQ9

O* = kinetic enery( 5 = mass( c = speed s&uared

2ork done liftin object = ain in A* = ain in O* of the object just before hittin

the round

Aower = work done/ time taken

Aower is the measure of how fast enery is transferred or transformed.

'he rowth of the world population means more people need warmth and food. ne

of the main enery resources available on our planet is its supply of fossil fuels.

*-amples include coal( oil and natural as. 'hey have been formed in the round

from dead veetation or tiny creatures by a process that has taken millions of years.

nce we have used them( it will take millions of years for new reserves of these

fuels to be formed. 'hey are therefore e-amples of nonBrenewable enery

resources.

! nonBrenewable enery resource is one that eectively can,t be replaces once it

has been used.

1urnin fossil fuels releases carbon dio-ide into the atmosphere. ;arbon dio-ide is a

reenhouse as. reenhouse ases trap the Sun,s heat in the *arth,s atmosphere

and cause the averae temperature of the atmosphere to rise. 'his eect is called

lobal warmin and causes chanes in the world,s and meltin of the polar ice caps.

5ost coal and oil contain some sulfur. 2hen they are burnt( they release sulfur

dio-ide. Sulfur dio-ide is then released into the atmosphere. It then combines with

water to form acid rain. It is possible to remove the sulfur from these fuels but his

costs lots of money. n the other hand( international areements are forcin

companies who emit lare &uantities of sulfur dio-ide to clean up their waste ases.

uclear reactors use uranium to produce enery. %or the nuclear reactor process( a

particular form or isotope of uranium is needed. !lthouh a reactor only needs a

small amount of uranium is needed( uranium is in limited supply. 'he uranium in the

*arth was formed before the solar system was formed( so once it has been used

there will be no further supplies. It is therefore cateori


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Stored

enery inthe formof fossil

fuels.;oal( as(

oil andnuclear

fuel.

+eatenery is

hihBpressuresteam.

5ovementenery ofrotatinturbine.

*lectricaleneryoutput.

'he disadvantaes of nuclear power are the risk of accidents and the problem of

disposal of radioactive materials once the power station has nished with.

*lectricity is not an enery resource because it has been enerated usin other

sources of enery.

5ost electricity used in the world is enerated in power stations like the ones shown

in 7@.

+ow electricity is eneratedJ

7. +eat from nuclear fuel or from burnin fossil fuels is used to heat water. 'his

produces hihBpressure steam that makes the blades of a turbine spin.9. 'he turbine is used to turn the enerator.:. 'he enerator enerates electricity.

! renewable enery source is one that will not run out. 2ood is an e-ample of a

renewable source of enery. !s wood is cut down( new fastBrowin trees are

planted to replace those cut down.

ame of enery !dvantaes Disadvantaes+ydroelectric power • 'he water isn,t Lused,

and therefore can be

reused over and over

aain.

•

'he power can becreated 9E/P without

the water runnin out.

• It is a very clean

source of enery as no

reenhouse ases are

created.

• 'hey are very

e-pensive to build and

must be built to hih

standard.

•

'he creation of damscan create Coods and

natural environments

will be destroyed.

• Alacin a damn in front

of a river can cause

neihborin countries

to lack access of water.

Spins

enerato

Drives

turbine

Gsed to

heat


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'idal enery • It can last for a lon

time

• 5aintenance is cheap

• It is ecofriendly as it

doesn,t create

reenhouse ases.

• ;ost of construction is

very hih

• +ih waves can

damae the plant

• Very limited to

locations ofconstructions

2ave enery • 'hey are renewable

because they will

never run out and

waves will always hit

the shore.

• 'hey are easily

predictable and can

show you how much

enery will beproduced.

• It is ecofriendly as it

doesn,t release any

reenhouse ases.

• 'hey can only be built

near cities and very

abundant areas so the

enery can be used

and not wasted.

• %or the enery to be

collected( lare load

machines are needed

which could disturb thehabitat of the sh.

• 'hey are much less

e6cient durin rouh

weather.2ind power • 2ind is free and

therefore renewable

• nce it is built( no

reenhouses or

pollutants are made

• 0emote areas can use

it as a source of enery

• 'he strenth of wind

isn,t constant and the

amount of enery is

therefore also not

constant.

• 'hey are supposedly

loud• 'hey are supposedly

noisySolar power • Sunliht is free so it is

renewable

• It doesn,t create any

pollution

• It can be used in

remote areas to

enerate enery

• Solar enery can only

be harnessed durin

sunny daytimes

• Solar panels are

e-tremely e-pensive

• Fare areas of land are

needed to capture as

much sunliht aspossible

eothermal enery • It is ecofriendly as it

doesn,t release any

reenhouse ases

• 'hey are not weather

reliant

• 'hey are renewable

• nly few sites have the

potential of eothermal

enery

• 'otal enery enerated

is too small

• It is very danerous


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sources of enery because there is the

risk of a volcano

eruptin

+ow this work is in the te-t book paes 7:B7@

SECTION E: So!ids' !i()ids and %ases

Solids are often very dense) they have a hih mass for a certain volume. Fi&uids are

often less dense than solids( and ases have very low densities.

Density = mass/volume

'he volume of an irreular object can be determined by usin a displacement can

and a measurin cylinder. It is easier to cut thins with a sharp knife than a blunt

one( because with a sharp knife all the force is concentrated into a much smaller

area. Aressure is dened as the force per unit area.

Aressure = force/ area

Some applications re&uire a low pressure( such as tractors and camel,s feet as they

are supposed to move over mud and sand and are not supposed to sink.

ases also e-ert pressure around them. 'he pressure e-erted by the atmosphere

on your body is about 7??(??? Aa. !n e-periment to prove this is by usin two lare

bowls. Kou place the two toether and pump the air out. 'he bowls couldn,t be

pulled apart( even when the horses tried. 'his is because when air is inside thespheres( the pressure is the same inside and outside. If the air is sucked out(

pressure is only actin from the outside. 'he hemisphere can,t be pulled apart until

air is let back into them.

Aressure dierence "Aa$ = heiht "m$ - density "k/m:$ - "/k$


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1rownian motion proves that particles in a li&uid or a as have continuous

movement. Aarticles of a li&uid or as are movin around continually and bump into

each other and into tiny particles such as pollen rains.

Aressure = 7/volume. +ere the pressure is inversely proportionally to volume.

1oyles is law) A7V7 = A9V9 this needs a -ed temperature and mass

ases can be compressed because the particles are very spread out. 2hen a as is

s&uashed into a smaller container it presses on the walls of the container with a

reater pressure. If the as is kept at the same temperature( the averae of the

particles stays the same. If the same number of particles is s&uee


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container are harder and happen more often. 'his results in the averae pressure

e-erted by the particles increasin.

2hen we cool a as the kinetic enery of its particles decreases. 'he lower the

temperature of a as the less kinetic enery its particles haveB they move more

slowly. !t absolute


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Kou can see the shape of the manetic eld around a manet by usin iron llins

or a plottin compass. Aut the manet beneath a piece of paper and add sprinkle

iron llins on top. %or the compasses( they will all be facin the South Aole.

'hese manetic lines of forceJ show the shape of the manetic eld( the direction of

the manetic eld and the strenth of the manetic eld as the closer the eld

lines( the stroner the manetic eld.

2hen a current Cows throuh a wire a manetic eld is created around the wire.

'his is called electromanetism. 'he eld around the wire is &uite weak and circular

in shape. 'he direction of the manetic eld depends upon the direction of the

current and can be found usin the rihtBhand rip rule.

'he strenth of the manetic eld around a currentBcarryin wire can be increased

by increasin the current in the wire or wrappin the wire into a coil or solenoid.

'he shape of the manetic eld around a solenoid is the same as that around a bar

manet. 'he positions of the poles can be determined usin the rihtBhand rip

rule.

'he strenth of the eld around a solenoid can be increased byJ increasin the

current Cowin throw throuh the solenoid( increasin the number of turns on the

solenoid and wrappin the solenoid around a manetically soft core such as iron.

'his combination is called an electromanet.

2hen the bell is pressed the circuit is complete and current Cows. 'he soft iron core

of the electromanet becomes maneti


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the iron armature moves( the hammer strikes the bell and at the same time a ap is

created at the contact screw. 'he circuit is incomplete and current stops Cowin.

'he electromanet is now turned o so the sprin,s armature returns to its oriinal

position. 'he circuit is complete and the whole process beins aain.

;ircuit breakers use electromanets to cut o the current if it becomes larer than acertain value. If the current is too hih the electromanet becomes stron enouh

to pull the iron catch out of position so that the contacts open and the circuit

breaks. nce the problem in the circuit has been corrected the catch is repositioned

by pressin the reset button.

2hen lare currents Cow in a circuit there is always daner of the user receivin a

severe electric shock. *ven turnin the circuit on/o is ha


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! voltae is produced when a manet moves in a coil of wire. 'his process is called

electromanetic induction.

It is not practical to enerate lare amounts of electricity by passin a manet in

and out of a coil of wire. Instead( enerators induce a current by spinnin a coil of

wire inside a manetic eld( or by spinnin a manet inside a coil of wire. !s thishappens( a potential dierence is produced between the ends of the coil( which

causes a current to Cow.

ne simple e-ample of a enerator is the bicycle dynamo. 'he dynamo has a wheel

that touches the back tyre. !s the bicycle moves( the wheel turns a manet inside a

coil. 'his induces enouh electricity to run the bicycleRs lihts.

! bicycle dynamo. 'he wheel of the dynamo rubs aainst the bicycle tyre to turn a

manet sited within a coil of wire. 'his enerates electricity to power the bicycleRs

lamps.

'he faster the bicycle moves( the reater the induced voltae B and the brihter the

lihts.

2hen a wire is moved in the manetic eld of a enerator( the movement(

manetic eld and current are all at riht anles to each other. If the wire is moved

in the opposite direction( the induced current also moves in the opposite direction.

0iht hand with thumb( forener and second ner at >? derees with arrows.

'humb shows direction of movement. %orener represents eld. Second ner

shows current from positive to neative.

%leminRs riht hand rule

In a enerator( one side of a coil moves up durin one half turn and then down

durin the ne-t half turn.

'his means that as a coil is rotated in a manetic eld( the induced current reverses

direction every half turn. 'his is called alternatin current "!;$.

It is dierent from the direct current "D;$ produced by a battery B which is always in

the same direction.

;urrent Cows in e-ternal circuit. 1rushes continuous contact between e-ternal

circuit( slip rins. Slip rins connected to coil. ;urrent induced in rotatin coil. 'he

coil rotated in manetic eld.


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;oil motion in an !; enerator

ormally in a enerator( the coil is -ed and mounted outside the manet( and it is

the manet which moves.

'he si


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Vp is the voltae applied to the primary coil in volts

s is the number of turns on the secondary coil

p is the number of turns on the primary coil

! transformer is an electrical device that chanes the voltae of an alternatin

current "!;$ supply( such as the mains electrical supply.

! transformer chanes a hihBvoltae supply into a lowBvoltae one( or vice versaJ

• a transformer that increases the voltae is called a stepBup transformer• a transformer that decreases the voltae is called a stepBdown transformer

'he ational rid

*lectricity is transferred from power stations to consumers throuh the wires and cables of

the ational rid.

2hen a current Cows throuh a wire some enery is lost as heat. 'he hiher the current(

the more heat is lost. 'o reduce these losses( the ational rid transmits electricity at

a low current. 'his needs a hih voltae.

Aower stations produce electricity at 9(??? V. *lectricity is sent throuh the ational rid

cables at E??(??? V( 9P(??? V and 7:9(??? V.

StepBup transformers are used at power stations to produce the very hih voltaes neededto transmit electricity throuh the ational rid power lines. 'hese hih voltaes are too

danerous to use in the home( so stepBdown transformers are used locally to reduce the

voltae to safe levels. 'he voltae of household electricity is about 9:? V.

'he ratio between the voltaes in the coils of a transformer is the same as the ratio of the

number of turns in the coils.

'his relationship can be shown by the followin e&uationJ

'his can also be written asJ


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StepBup transformers have more turns on the secondary coil than they do on the primary

coil.

StepBdown transformers have fewer turns on the secondary coil than they do on the

primary coil.

*lectrical power is calculated by multiplyin voltae "in volts$ by current "in amps$.

If a transformer is 7??N e6cient( then the input power will e&ual the output power. 'his

can be shown in the followin e&uationsJ

Input power = output power

Input "primary$ voltae input "primary$ current = output "secondary$ voltae output

"secondary$ current

VAIA = VSIS

2hereJ

VA is input "primary$ voltae

Ip is input "primary$ current

Vs is output "secondary$ voltae

Is is output "secondary$ current

SECTION G: +adioacti$it" and ,artic!es

!toms are made up of electrons( protons and neutrons. 'he electron is a very liht particle

with very little mass. It has a neative chare. *lectrons orbit the nucleus of the atom. 'he

nucleus is very small compared to the si


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Arotons and neutrons are also called nucleons because they are found in the

nucleus of the atom.

!tomic particle Aarticle mass 0elative chare*lectron 7 B7 neativeAroton 9??? 87 positiveeutron 9??? ? neutral

'he nucleus of an atom is surrounded by electrons. 'he electrons are movin

rapidly around the nucleus in a cloud or shell. !n atom is electrically neutral. 'his is

because the number of positive chares carried by the protons in its nucleus is

balanced by the number of neative chares on the electrons in the electrons in the

electron around the nucleus.

'he chemical behavior and properties of a particular element depend upon how the

atoms combine with other atoms. 'his is determined by the number of electrons in

the atom. 'he atomic number of an element of an element tells us how many

protons each of its atoms contains. %or e-ample( carbon has T protons in its nucleus

B the atomic number of carbon is therefore T. 'he atomic number is sometimes

called the proton number. 'he atomic number is iven the symbol U.

'he total number of protons and neutrons in the nucleus of an atom determines its

atomic mass. 2e refer to the mass of an atom by its mass number of nucleon

number) this number is the total number of protons and neutrons in the atom. 'he

mass number of an element is iven the symbol !.

*ach particular type of atom will have its own atomic number( which identies the

element.

5ass number( ! = number of neutrons 8 number of protons = number of nucleons

umber of neutrons = number of nucleons # number of protons = !B U

'he number of protons in an atom identies the element. 'he chemical behavior of

an element depends on the number of electrons it has which is the same as the

number of protons in the nucleus. 'he number of neutrons in the nucleus can vary

slihtly. !toms of an element with dierent numbers of neutrons are called isotopes

of the element. 'he number of neutrons in in a nucleus aects the mass of the

atom. Dierent isotopes of an element will all have the same atomic number( butdierent mass numbers.

Isotopes of an element have dierent physical properties from other isotopes of the

same element. 'he dierences are the mass and the stability of the nucleus.

'he protons are held in the nucleus by the nuclear force. 'his force is stron enouh

to hold the nucleus toether aainst the electric force repellin the protons away


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from each other( the presence of neutrons in the nucleus aects the balance

between these forces. 'oo many or too few neutrons will make the nucleus unstable.

!n unstable nucleus will eventually decay. 2hen the nucleus of an atom decays it

ives out enery and may also ive out alpha or beta particles.

2hen unstable nuclei decay they ive out ioni


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0adiation Ioni


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beta particle( an electron( has practically no mass so the mass number( !( is the

same in H and K. !s the beta particle has a chare of B7( the atomic number of the

new element is increased to U87.

amma decayJ

amma radiation is hihBenery electromanetic radiation) after an unstable

nucleus has emitted an alpha or beta particle it sometimes has surplus enery. It

emits this enery as amma radiation. amma rays are pure enery( so they do not

have any mass or chare. 2hen a nucleus emits a amma ray there is no chane to

either the atomic number or the mass number of the nucleus.

'he 1ec&uerel is a measure of how many unstable nuclei are disinteratin per

secondB one 1ec&uerel means a rate of one disinteratin per second.

Ahotoraphic lm is still used to detect radioactivity. Scientists that use radioactive

material wear a strip of photoraphic lm in a bade. If the lm becomes foy( it

means that the scientist has been e-posed to a certain amount of radiation. 'hese

bades have to be reularly checked.

'he eierB5uller tube is a tube used to measure the level of radiation. It is a lass

tube with an electrically conductin coatin on the inside surface. 'he tube has a

thin window made of mica. 'he tube is contains a special mi-ture of ases at very

low pressure. In the middle of the tube( electrically insulated from the conductin

coatin( there is an electrode. 'his electrode is connected( via a hih value resistor(

to a hihBvoltae supply( typically :??B?? V.

2hen ioni


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ne form of uranium is a radioactive element that decays very slowly. 'wo of tis

decay products are ases. 'hese are the radioactive ases radon and thoron.

0adonB999 is a hihly radioactive as produced by the decay of radiumB99T. 'horon

or radiumB99? is an isotope of radium formed by the decay of a radioactive isotope

of thorium.

!s these decay products are ases( they seep out of radioactive rocks.

Violent nuclear reactions in stars and e-plodin stars called supernovae produce

very eneretic particles and cosmic rays that continuously bombard the *arth.

Fower enery cosmic rays are iven out by the sun.

'he atoms that make up our bodies contain radioactive atoms that were created

millions of years ao when the solar system was created. 2e also breathe in tiny

amounts of the radioactive isotope of carbonB7E.

2e use articial materials for many purposes. eneratin electricity in nuclear

power stations has been responsible for the leakin of radioactive material into the

environment. 0adioactive tracers are used in industry and medicine. 0adioactive

materials are also used to treat certain forms of cancer. +owever the majority of

radiation is naturalB the amount produced from medical and civil use in industry is

very small indeed.

0adioactive decay is a random process. It is impossible to tell which nuclei will

disinterate at any particular time.

'he radioactive decay raph is an e-ponential decay as it is decreasin

proportionally.

'he halfBlife of a radioactive sample is the averae time taken for half the oriinal

mass of the sample to decay. 'he halfBlife is dierent for dierent radioactive

isotopes.

!fter one halfBlife period( the amount of the oriinal unstable element is halved.

!fter a second period of time( the amount have halved aain.

'o measure the halfBlife of a radioactive material we must measure the activity of

the sample at reular times. 'his is done usin a eierB5uller tube linked to a rate

meter. 1efore takin measurements( we must subtract the backround radiation

from the measurements. 2e then measure the rate of decay of the sample atreular time intervals. 'he rate of decay is shown by the count rate on the rate

meter. Isotopes with shortBlives are suited to medical use. 'his is because the

activity of a source will rapidly become very small as the isotope decays &uickly.

0adioactive isotopes are used as tracers to help doctors identify diseased orans. !

radioactive tracer is a chemical compound that emits amma radiation. 'he tracer

is taken in orally or injected. Its passae around the body can then be traced usin


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amma ray camera. ! short halfBlive is important as this means that the activity of

the tracer decreases to a very low level in a few days. !n e-ample of this is iodineB

79: which is absorbed by the thyroid land.

ther isotopes are used to imae specic parts of the body. %or e-ample the

technetiumB>> is used in medical imain. It is used to help identify medicalproblems that aect many parts of the body.

0adiation from isotopes can have various eects of the cells that make up or bodies.

Fow doses of radiation may have no lastin eect. +iher doses may cause the

normal function of cells to be chaned. 'his can lead to abnormal rowth and

cancer. Very hih doses will kill livin cells.

;ancer can be treated by surery that involves cuttin out cancerous cells. !nother

way of treatin cancer is to kill the cancer cells inside the body. 'his is done with

chemicals containin radioactive isotopes. Gnfortunately( both the cancerous and

the livin cells die. 'o reduce the damae to healthy tissue( chemicals are used to

directly taret the location of the cancer in the body. 'hey may emit either alpha or

beta radiation. 1oth types of radiation have a short rane in the body so they only

aect a small volume of tissue close to the taret. 'he radioisotope iodineB7:7 is

used in the treatment of various diseases of the thyroid land. It has a halfBlife of

about eiht days and decays by beta particle emission.

Ioni


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dust miht cause false readins with an optical auin system. ;oal dust is much

less dense than coal so the amma ray system still works properly. !nother

e-ample of auin uses a similar process to monitor the thickness of plastic

sheetin and lm. 'he thicker the sheet( the reater the amount of radiation it

absorbs. 1y monitorin the amount of radiation( the thickness of the sheetin can

be closely controlled durin manufacture.

'racin and measurin the Cow of li&uids and asesJ radioisotopes are used to track

the Cow of Cuids in industrial processes. Very tiny amounts of radiation can easily

be detected. ;omple- pipin systems( like heat e-chaners in power stations( can

be monitored for leaks. 0adioactive tracers are even used to measure the rate of

dispersal of sewae.

0adiocarbon datin is used to nd the ae of oranic matter such as trees and

animals.

0adiocarbon datin measures the level of an isotope called carbonB7E. 'his is made

in the atmosphere. ;osmic rays from space are continually rainin down upon the

*arth. 'hese have a lot of enery. 2hen they strike atoms of as in the upper layers

of the atmosphere( the nuclei of the atoms break apart. 'he parts Cy o at hih

speed. If they strike over other atoms they can cause nuclear transformations to

take place. 'hese transformations turn the elements in the air into dierent

isotopes. ne such collision involves a fastBmovin neutron strikin an atom of

nitroen. 'he nuclear e&uation for this process isJ

7E(P 8 7(?n B 7E(T ; 8 7(7p

7( ? n represents a neutron. 7(7p represents a proton.

'he result of the collision of a neutron with a nitroen atom is a nuclear

transformation. 'he nitroen atom is transformed into an atom of the radioactive

isotope of carbon( carbonB7E. ;arbonB7E also reacts with o-yen in the atmosphere

to form carbon dio-ide which is then absorbed by plants in the process of

photosynthesis. 'he animals then eat the plant and it is now in a food chain. 'hese

carbonB7E atoms will decay( but in livin plants and animals( they are continuously

replaced by new ones.

2hen a livin oranism dies( the replacement process stops. !s time passes( the

radioactive carbon decays and the proportion of radioactive carbon in the remains

of the plant or animal( compared with the stable carbon isotope( decreases.

'here are limitations to the method of radiocarbon datin. It assumes the level of

cosmic radiation reachin the *arth is constant( which is not necessarily an accurate

assumption. %ortunately( the techni&ue has been calibrated to take the variations of

cosmic ray activity into account. 'his is done by testin samples of a known ae(

kike material from the mummies of *yptian Aharaohs. 'he radiocarbon method is


35/39

not used to date samples older than ?(???BT?(??? years because( after 7? halfB

lives the amount of carbonB7E remainin in samples is too small to measure

accurately.

In oranic( nonBlivin matter doesn,t absorb carbonB7E( so dierent techni&ues must

be used for ndin out the ae of rocks and minerals. 2hen a radioactivesubstance decays it transforms into a dierent isotope( sometimes of the same

element( sometimes a dierent element. 'he oriinal radioisotope is called the

parent nuclide and the product is called the dauhter nuclide. 5any of the products

of decay( the dauhter isotopes( are also unstable and these too decay. 'his means

that as the parent isotope decays its breeds a whole family of elements in what i

called a decay series. 'he end of the decay series is a stable isotope.

'he table shows some radioactive parent isotopes with the stable dauhters formed

at the end of their particular decay series.

0adioactive parent isotope Stable dauhter element +alfBlife "years$AotassiumBE? !ronBE? 7.9 billion 'horiumB9:9 FeadB9?@ 7E billionGraniumB9: FeadB9?P P?E billionGraniumB9:@ FeadB9?T E.EP billion;arbonB7E itroenB7E T@

Ioni


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In all cases( the loner the period of e-posure to radiation the reater the risk of

serious cell damae. 2orkers in the nuclear industry wear bades to indicate their

level of e-posure. Some are strips of photoraphic lm that become increasinly

Lfoy, as the radiation e-posure increases. !nother type of bade uses a property

called thermoluminescence. 'hermoluminescence means that the e-posed material

will ive out liht when it is warmed. 'he radiation releases enery to make heat sothe thermoluminescencent bades ive out more liht when e-posed to hiher

levels of radiation.

Arecautions that must be followed to safely handle radioactive materialsJ

'he samples are stored in lead containers to block even the most penetratin form

of radiation( amma rays. 'he containers are clearly labeled and must be stored in

a locked metal cabinet. 'he samples are handled usin tons and are kept as far

from the body as possible. In nuclear industry and research laboratories( much

larer amounts of radioactive material are used. 'hese have to be handled with

reat care. Very eneretic sources will be handled remotely by operators who areshielded by lead( concrete and thick lass viewin panels.

'he major problem with nuclear materials is lonBterm storae. Some materials

have e-tremely lon halfBlives so they remain active for thousands and sometimes

tens of thousands of years. uclear waste must be stored in sealed containers that

must be capable of containin the radioactivity for enormously lon periods of time.

Dalton thouht that the atom is a solid sphere.

M.M. 'hompson thouht that atoms were positively chared spheres with neatively

chared electrons embedded into them.

*rnest 0utherford red alpha particles at very thin old foil. !lpha particles are

positively chared particles iven o by some

radioactive substances.


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'he


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'he framents of this decay are two dauhter nuclei of bariumB7EE and kryptonB@>.

'he decay also produces amma radiation and three more neutrons. 'he e&uation

for this decay isJ

'he ssion reaction produces a hue amount of enery. 'his is because some of the

mass of the oriinal uraniumB9:T nuclei is converted to enery. 5ost of the enery

is carried away as the kinetic enery of the two lihter nuclei. Some is emitted as

amma radiation. 'he three neutrons produced by ssion may hit other nuclei of

uraniumB9: and therefore causin the process to repeat. If one neutron from each

ssion causes on nearby uraniumB9: to split( then the ssion reaction will keepoin.

'his is called a chain reaction. If this reaction is allowed to take place in an

uncontrolled way( the result is a nuclear e-plosion. 'his involves the sudden release

of enormous amounts of heat enery and radiation. In a nuclear reactor the process

is controlled so that heat enery is released over a lon period of time. 'he heatproduced in the core or heart of the reactor is used heat water. 'he steam produced

then drives turbines to turn enerators.


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'he reactor core

contains fuel rods of enriched uranium. *nriched uranium is uraniumB9:@ with a

hiher proportion of uraniumB9: than is found in natural reserves of uranium.

'he job of the moderator is to absorb some of the kinetic enery of the neutrons to

slow them down. 'his is because slow neutrons are more easily absorbed by

uraniumB9:. 'he slowin of neutrons therefore starts the ssion process.

In the nuclear reactor there are also control rods( made of boron or cadmium. 'hese

absorb the neutrons and take them out of the ssion process completely.

'he waste products present a serious damae for lonBterm storae. 'hey are

usually stored in contains that are buried under round. 'he rocks must be

impermeable to water and the eoloy of the site and must be stable. 'heyshouldn,t be placed in areas such as earth&uake

Physics Study Notes Igcse Edexcel

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