1026899 Nota Padat Fizik F5 Electromagnet

5/26/2018 1026899 Nota Padat Fizik F5 Electromagnet

1/36

3.1 MAGNETIC EFFECT OF A CURRENT-CARRYING CONDUCTOR

What is an

electromagnet?

An electromagnet can be made by sending an electriccurrent through a coil of wire wound around an iron

core.

When a current flows through the coil, it produces amagnetic field. The soft iron core becomes

temporarily magnetized when the current is switchedon.When the current is switched off, it loses itsmagnetism.

What is amagnetic fieldpattern?

A magnetic field pattern can be represented by fieldlines that show the shape of the field.Magnetic field lines which are close together representa strong field.The field direction is defined as the direction indicatedby a compass needle placed in the magnetic field.

Determine thedirection of themagnetic fieldaround acurrent-carrying wire

The Right-Hand Grip RuleGrip the wire using the right hand, with your thumbpointing in the direction of the current. Your otherfingers now point round the wire in the direction of themagnetic field.When the direction of the current is reversed, themagnetic field direction also is reversed.

61


2/36

Activity 1

Aim Draw the magnetic field pattern due to a current in a 1.straight wire,2. coil 3. solenoidDetermine the direction of the magnetic field.

Pro

cedure

1. Use small plotting compasses and place them on thecardboard to determine the direction of the magnetic field.

2. Observe and sketch the pattern produced.3. Reverse the current supply connections to see its effect on

the compass needle.4. Remove the compasses and springkle iron filings onto the

cardboards and tap the sheets gently with a pencil. Sketchyour observation.

StraightWire

62


3/36

Co

il

Solenoid

Note:The right hand grip rule for a

solenoid:The thumb points towards northpole of the magnetic field while theother fingers indicate the directionof the current in the solenoid.

63


4/36

State thefactors thataffect the

strength of theelectromagnet.

Describe application of Electromagnet

64

Electric Bell

When the bell push ispressed, a current flows inthe coils of theelectromagnet, causing it to

be magnetized. The magnetized

electromagnet attracts thesoft-iron armature, causingthe hammer to strike thegong.

The movement of thearmature breaks the contactand causes the

electromagnet to lose itmagnetism.

The light spring pulls thearmature back, remaking thecontact and completing thecircuit again.

The cycle is repeated so long as thebell push is pressed and continuousringing occurs.

Magnetic Relay

A solenoid switch worked byan electromagnet. It is usedin a circuit which controls theoperation of another circuit,especially if the current islarge in the second circuit.

Circuit 1 requires only asmall current.

When the switch is closed,current flows in the coil,

causing the soft-iron core to be


5/36

The movement of the ironarmature closes the contactsin the second circuit. Circuit2 is now switched on.

Circuit 2 may have a largecurrent flowing through it tooperate powerful motors orvery bright lights.

magnetized and attracts the amarture

The advantage of using a relay is thaa small current (circuit 1) can beused to switch on and off a circuit

with a large current (circuit 2). This is useful for two reasons:

(b) circuit 1 may contain a componensuch as a light detecting resistor(LDR), which uses small currents.

(c) Only the circuit with a largecurrent needs to be connectedwith thick wire.

Telephone Ear-piece

The varying current from themicrophone flows throughthe coils of an electromagnetin the earpiece.

This pulls the iron diaphragmtowards the electromagnetby a distance which dependson the current.

As a result, the diaphragm moves inand out and produces sound waves thaare replicas of those that entered themicrophone.

Circuit Breaker

Acts as an automatic switchthat breaks open a circuitwhen the current becomestoo large.

In a household circuit, thecurrent may becomeexcessive when there is a

short circuit or an overload. The strength of the magnetic

field of the electromagnetincreases suddenly.

The soft iron armature ispulled towards theelectromagnet.

This results in the spring pullingapart the contacts. The circuit isbroken and the current flow stopsimmediately.

After repairs have been made, thereset button is pushed to switch onthe supply again.

65


6/36

3.2 THE FORCE ON A CURRENT-CARRYING CONDUCTOR IN AMAGNETIC FIELD

An electric current produces a magnetic field around it.

When a wire carries an electric current through anothermagnetic field, a force is exerted on the wire.

The magnetic force on a current-carrying conductor is in amagnetic field is due to the combination of the magneticfield due to the current in the conductor and the externalmagnetic field to produce a resultant magnetic field.

Describe

whathappens tocurrent-carryingconductorin amagneticfield The direction of the

magnetic force, F, actingon the wire can be

determined by usingFlemings left-hand rule.

What isFlemingsLeft

Hand Rule

If the forefinger, secondfinger and the thumb of theleft hand are extended at

right angles to each other,with the forefinger in thedirection of the magneticfield, the second finger inthe direction of the current,then the thumb will pointthe direction of the force, For motion.

66


7/36

To investigate the force on a current-carrying conductor in a magneticfield.

Procedure

1. Switch on the current and observe what happens to the shortcopper wire.

2. Reverse the connections of the voltage supply. Observe whathappens to the copper wire.

3. Reverse the magnetic field and repeat step 2 and 3.4. Align the magnetic field so that it is parallel with in the short

copper wire.

Indicated the flow of current using arrows. Show the direction ofmagnetic field and indicate the direction where the short copperwire will move. Prove the direction of the force using theFlemings left-hand rule.

step 1 step 2 step 3Observation

Step 4 The direction of magnetic field is parallelto the direction of current.The shor t wire stays at rest.

67


8/36

Conclusion When a current-carrying conductor is in a magnetic field of a

permanent magnet, the interaction between the two magneticfields produce a force on the conductor.

The direction of the magnetic field, the current and the forceacting on a conductor is perpendicular to each other.

Describehow acurrent-carryingconductorin amagnetic

fieldexperiencesa force.

The magnadur magnets produce a uniform, parallelmagnetic field.

The current-carrying vertical wire produces a circularmagnetic field around itself.

The two fields interact to produce a resultant magneticfield known as a catapult field.

Upward, the two fields are in the same direction andthey produce a stronger combined field.

Downward, the two fields act in opposite directionsand the combined field is weaker.

The wire carrying a current thus experiences aresultant force in the direction from the stronger to theweaker field, i.e from upward to downward.

68


9/36

Explain the factorsthat affect themagnitude of theforce on a current-carrying conductor ina magnetic field.

The magnitude of the force on a current-carrying conductor in a magnetic field dependson:

1. the size of the current in the conductor2. the strength of the magnetic field

Draw a pattern of resultant magnetic field or catapult field for a current-carrying coil in a magnetic field.

69


10/36

Show the direction of the resultant force, F.

What will happen to the coil?

The coil will rotate clockwise.

Describehow adirectcurrentmotorworks

Commutator: reverse thedirection of current in the coilevery half rotation so that thecoil continues to turn in samedirection

Carbon Brush: to contact with

the commutator so the currentfrom the battery enters the coil.

Spring: push the brush so it willalways contact with thecommutator.

70


11/36

Show

thedirectionof thetwoforcesacted onthe coil.

1. When current flows through thehorizontal coil, magnetic field isproduced around it.The interaction between the magnetic

field of the current and the magnetic fieldof the permanent magnet produces acatapult field and 2 turning force. Thedirection of the force is determined byFlemings left-hand rule. The two forcesproduce a couple which rotates the coil.

2.When the coil gets to the uprightposition, the contact between the carbonbrushes with the commutator is broken.

There is no turning force on it becauseno current flows in the coil. But the coilcontinues to rotate because of its inertia.

3.When the coil in a horizontal positionagain, the sides of the coil changesposition. The commutator reverses thedirection of the current in the coil toensure that the forces on the coil turn the

coil in one direction only. So the coil isstill rotating in the same direction.

4. The above processes are repeated andthe motor continues to rotate.

Factorswhichaffectthe

speed ofrotationof themotor

Factors Speed of rotation of themotor

1. Increasing the size of the

current

Increases

2. Increasing the strength ofthe magnetic field

Increases

3. increasing the number ofturns

Increases

4. Increasing the area of thecoil

Increases

71


12/36

3.3 ELECTROMAGNETIC INDUCTION

Describeelectromagnet

induction

How inducedcurrent isproduced?

Electromagnetic induction is the production of anelectric current by a changing magnetic field.

The induced current is produced only when there isrelative motion between the conductor / coil and themagnetic field lines.

The relative motion of a conductor across a magneticfield can be produced by:(a) moving a straight wire quickly across a magnetic

field between two flat magnets.

(b) Moving a permanent magnet towards one end of asolenoid.

Each time the straight wire cuts across the magneticfield, or the permanent magnet moves towards thesolenoid, a current is induced in the coil and adeflection is observed in the sensitive galvanometer.

This current is called induced current. Theelectromotive force that is produced is called theinduced e.m.f.

72


13/36

A. Electromagnetic Induction in a straight wire.

Procedure:1. Hold the copper rod

stationary between the poles

of the magnet. Observe thereading of the galvanometer.2. Move the rod quickly in

Direction 1. Observe thedeflection of thegalvanometer.

3. Repeat step 2 for the otherdirections.

If a galvanometer shows a deflection, it means there is an inducedcurrent produced

Current is induced in a straight conductor when it moves and cutsthe magnetic field lines.

The motion of the copper rod must be perpendicular to the directionof the magnetic field lines so that an induced current will beproduced.

B. Electromagnetic Induction in a solenoid.

1. Push the bar

magnet into thesolenoid. Observethe deflection of thegalvanometer.

2. Hold the bar magnet

stationary in thesolenoid. Note thereading of thegalvanometer.

3. Now pull the bar

magnet out of thesolenoid. Observethe deflection of thegalvanometer.

The galvanometer showed a positive reading when the bar magnetand solenoid were coming closer to each other. This shows that acurrent is produced in the solenoid in certain direction.

73


14/36

The galvanometer showed a negative reading when the magnet andsolenoid were moving fur ther away from each other. This shows thata current is produced in the solenoid in the opposite directions.

A current is induced in a solenoid when there is relative motionbetween the solenoid and a magnet.

ConclusionCurrent is induced in a straight conductor when it moves and cuts themagnetic field lines.Current is induced in a solenoid when there is relative motion betweenthe solenoid and a magnet.

Indicate the

direction ofthe inducedcurrent in astraight wire

Flemings right-hand rule:

If the thumb and the first twofingers on the right hand areheld at right angles to eachother with the first fingerpointing in the direction ofthe magnetic field and thethumb in the direction of themotion, then the secondfinger points in the direction

of the induced current.

A wire PQ is movedvertically downwards in amagnetic field. ApplyingFlemings right-hand rule,the induced current willflow from P to Q.

Indicate thedirection ofthe inducedcurrent in asolenoid.

Lenzs Law:The direction of the induced current in a solenoid issuch that its magnetic effect always oppose the changeproducing it.

74


15/36

Magnet ismoved

towards thesolenoid

Magnet ismoved awayfrom thesolenoid

Lenzs Lawfor solenoid

Principle ofConservationof Energy

Relative motion betweenmagnet and solenoid

Polarity at the end of thesolenoid facing the magnet

Toward each other Same polarity as the magnet

Away from each other Opposite polarity as themagnet

Lenzs law is an example of the Principle ofConservation of Energy. When the magnet or solenoidis moved against the opposing force, work is done.Therefore mechanical energy is converted to electricalenergy.

75


16/36

Explainfactors thataffect themagnitude of

the inducedcurrent.

Faradays Law:The size of the induced e.m.f is directly proportional tothe rate at which the conductor cuts through themagnetic field lines.

The size of the induced e.m.f. and thus the inducedcurrent and be increased by:1. moving the magnet or the solenoid at a higher speed2. increasing the number of turns on the solenoid3. increasing the strength of the magnetic field through

the use of a stronger magnet.

Show the correct direction of the induced current when the magnet is

moved in the direction shown.

76


17/36

What is the direction of the inducedcurrent? Determine the poles at P and Q.

77

Describe

applications ofelectromagneticinduction

Current Generator

Current generator functions by convertingmechanical energy to electrical energy. Current generator works based on electromagnetic

induction and uses the Flemings Right hand rule.

Current generator is divided into: direct currentgenerator and alternate current generator.

Direct CurrentGenerator

Commutator: reverses the connections of the coilwith the external circuit after every half cycle, sothat the current in the outside circuit always flowsin the same direction.


18/36

Describe how does a direct current generator work. Show the directionof movement of the coil AB and CD. Mark the direction of the inducedcurrent in the coil and the galvanometer.

Coil AB moves ., coil CDmoves..

When the coil rotates, its sidescut across the magnetic fieldlines and induced current flowsin the coil from .

The galvanometer will deflect to

The sides AB and CD aremoving .to the

magnetic field and thus do not..the magnetic field lines.

No . ..isproduced at the instant.

The galvanometer returns tomark.

Asthe coil continuesto rotate,current will again be induced inthe coil but its direction in now

opposite to that in figure 1 whichis from .. to .. and from to

However, the direction of thecurrent through the externalcircuit remains the same, so thegalvanometer deflects to the

The sides AB and CD aremoving .to themagnetic field and thus do not

..the magnetic field lines. No . ..is

produced at the instant. The galvanometer returns to

mark. The process is ..

78


19/36

The inducedcurrent varies froma maximum tozero, it flows in

one direction only.Hence, the inducedcurrent is called adirect current.

AlternatingCurrentGenerator

The two ends of the coil are connected to two sliprings which rotate with the coil.

Each slip ring is always in contact with the samecarbon brush.

79

Describe how does an alternating current generator work. Show thedirection of movement of the coil AB and CD. Mark the direction of theinduced current in the coil and the galvanometer.


20/36

80

Coil AB moves ., coil CD

moves..

When the coil rotates, its sides cutacross the magnetic field lines and

induced current flows in the coilfrom to .. and from to (using Flemings right handrule)

In the external circuits, currentflows from .. to .

The sides AB and CD aremoving .to themagnetic field and thus donot ..the magnetic fieldlines.



After the vertical position, thecurrent increases until it attains the

maximum value when the coil is ina horizontal position. Coil CD moves , coil AB

moves . The direction of the induced

current is from .. to .. and from to

The direction of the currentthrough the external circuit is from

The sides AB and CD aremoving .to the

magnetic field and thus donot ..the magnetic fieldlines.



The process is ..


21/36

the brush to which isreversed.

The output current generated is an alternating current because thecurrent changes direction in the external circuit each time the coilpasses the vertical position.

Assume the current flows from P to Q is positive and the currentflows from Q to P is negative.

The current changes I magnitude and direction after every halfrotation.

81


22/36

Compare direct current and alternating current.

1. A direct current is a current thatflows in one direction only in a

circuit.2. The magnitude of a directcurrent may be:

(a) constant(b) changes with time

1. An alternating current is acurrent which flows to and fro in

two opposite directions in acircuit. It changes its directionperiodically.

A direct current can flow through aresistor but cannot flow through acapacitor.

An alternating current can flowthrough both a resistor and acapacitor.

Both the direct current and alternating current have a heating effect onthe filament of a bulb and can light up the bulb.

82


23/36

The current increases from zeroto a maximum value of + Io(atA), and back to zero at B. It thenreverses direction and

increases to - Ioat C and back tozero again.Io = peak current,

Vo= peak voltage

The time taken for a completecycle from O to D is called oneperiod, T.

Frequency of the current is fwhere f = 1/T

In Malaysia, the frequency of thea.c supply is 50 Hz.Hence, the period of the a.c is :T = 1/50 = 0.02 seconds.

Figure shows an alternatingcurrent with a magnitude thatchanges with time.

(a) What is the peakcurrent?

(b) What is the period of thea.c. current?

(c) What is the frequency ofthe a.c current?

83


24/36

8.4 TRANSFORMERS

What is atransformer?

A transformer is an electrical device which increases ordecreases an alternating voltage based on the principle

of electromagnetic induction.Describe thestructure of asimpletransformer

A transformer consists of two coils of wire woundround separately on a laminated soft-iron core.

The coil connected to the input voltage is called theprimary coil. The coil connected to the outputvoltage is called the secondary coil.

The purpose of the common iron core is to provide amagnetic field linkage in the secondary coil.

Describe theoperatingprinciple of asimpletransformer

A transformer works on the principle ofelectromagnetic induction.

When a.c voltage, Vp, is applied to the primary coil oftransformer, an alternating current flows through thecoil. The soft-iron core is magnetized in one way andthen the other.

This means that the magnetic flux linkage in thesecondary coil is constantly changing.

An alternating e.m.f is induced across it to producean a.c voltage, Vsin the secondary coil and a.ccurrent flows through the second coil.

The frequency of the secondary voltage Vsis thesame as that of the primary voltage, Vp.

The magnitude of the secondary voltage, Vs, dependson the ratio of the number of turns of the primary andsecondary coils.

84


25/36

Why does thetransformernot work witha d.c power

supply?

A current is induced in the secondary coil only whenthere is a changing magnetic flux due to a changingprimary current. (changes direction and magnitude)

A d.c. power supply gives a constant current in theprimary circuit

A constant direct current whose magnitude anddirection is constant does not create a changingmagnetic flux in the secondary coil.

Therefore electromagnetic induction does not takeplace.

State therelationshipbetweennumber ofturns in coilswith voltagein atransformer,(Vp, Np, Vsand Ns)

According to Faradays law:Voltage number of turns in coils

kN

V

kNV

NV

=

=

s

s

p

p

N

V

N

V=

Vp= input (primary) voltageVs= output (secondary) voltageNp= number of turns in the primary coilsNs= number of turns in the secondary coils

Compare andcontrast astep-uptransformerand a step-downtransformer

Step-up transformerIf Nsis greater than Np, then Vsis greater than VpStep-down transformerIf Nsis lower than Np, then Vsis lower than Vp

85


26/36

Step-up transformer Step-down transformer

Ns> NpVs> Vp

Ns< NpVs< Vp

86

What is the

relationshipbetweenoutput powerand inputpower of anidealtransformer?

A transformer transfers electrical power from theprimary circuit to the secondary circuit.

The primary circuit of a transformer receives power ata certain voltage from the a.c power supply. Thetransformer delivers this power at another voltage toan electrical device connected to the secondarycircuit.

In an ideal transformer, there is no energy loss duringthe process of transforming the voltage.

[Power supplied to = [Power used in thethe primary coil] secondary coil]

Input power = Output powerVpIp = VsIs

Describe theenergy losesin atransformer

In a real transformer, some energy is lost in thetransformer especially in the form of heat.

The output power is less than the input power. Therefore the efficiency of the transformer is less

than 100%.


27/36

Efficiency ofa transformer

Efficiency = output power X 100%Input power The power loss is due to

(a) heating of coils(b) eddy currents in the iron core(c) magnetization and demagnetization of core(d) leakage of magnetic flux.

Causes of energy loss in

transformers

Ways to improve the efficiency of

a transformerResistance of the coils

all coils will have resistance heat is produced when current

flows through them

Use thick copper wires to makethe coilsThe resistance will reduce as thewire is thicker.

Eddy currents in the core

the changing magnetic field willalso induces current in theiron core

this induced current is callededdy current

cause heat to be produced inthe iron cores.

Use laminated cores to reduceeddy currents

Magnetization anddemagnetization of the core

the alternating current flowingthrough the transformercontinually magnetizes anddemagnetizes the core

work has to be done to changethe magnitude and direction ofthe magnetic field in the corewhich contributes to energyloss

Use cores made from soft-iron assoft-iron core can be easily

magnetized and demagnetized.

87


28/36

Leakage of magnetic field

electrical energy is lost when afraction of the magnetic fieldproduced by the primary coil

does not link with thesecondary coil.

Wind the secondary coil on top ofthe primary coil

Solve problems involving transformers

1. A transformer is required to stepdown the mains voltage of 240 Vprovide a 12 V supply for an electrictoy. If the primary coil is wound with1 000 turns of wire, calculate thenumber of turns required for thesecondary coil.

2. A step up transformer has 10 000turns on its secondary coil and 100

turns on its primary coil. Analternating current of 5.0 A flows inthe primary coil when it is connectedto a 12 V a.c supply. Calculate:(a) the input power to the

transformer(b) the e.m.f induced across the

secondary coil.(c) What is the maximum current that

could flow in a circuit connectedto the secondary coil if thetransformer is 100% efficient.

88


29/36

89

8.5 GENERATION AND TRANSMISSION OF ELECTRICITY

Electricity is generatedin power stations, transmitted(sent) throughlong-distance cables, and then distributedto consumers.

Listsources ofenergyused togeneratedelectricity

Renewable energy sources : an energy resourcethat is continually replaced and will not run out.

Non-renewable sources: an energy resource thatcannot be replaced once it has been used.

Renewable energy Non-renewable energy

Describethe variousways ofgenerating

electricity

Coal-firedpowerstation

Gas-firedpowerstation

Electricity is produces using generators A generator has a huge magnet that is turned by

a turbine.

As the magnet turns inside a coil of wire,electricity is produced by electromagneticinduction.

Many sources of energy are used to turn theseturbines.

1. Coal is burned and the heat energy is used toproduce high pressure steam.

2. The steam produced is used to drive thegenerators to produce electricity.

3. The energy changes: chemical energy to heatenergy to kinetic energy to electric energy

1. The burning of natural gas produces highpressure steam that is used to drive turbines.

2. The energy changes: chemical energy to heatenergy to kinetic energy to electric energy


30/36

Hydro-electricpowerstation

Nuclearpowerstation

Biomass

Solar

Windgenerator

1. A huge dam is built across rivers to containwater.

2. When the water in the dam is allowed to flowdown to a lower level, the kinetic energy of the

moving water is used to drive water turbines,which in turn drive the generators to produceelectricity.

3. The energy changes: potential energy to kineticenergy to electric energy

1. Energy from nuclear fission (splitting ofuranium 235 atoms) is used to produce highpressure steam to drive turbines

2. The energy changes: nuclear energy to heatenergy to kinetic energy to electric energy

1. Biomass includes rotting plants and agriculturalwastes such as oil palm kernels and householdsewage that are used to produce methane gasand alcohol.

2. Heat energy from the burning of biomass isused to generate electricity

1. Solar energy originates from the sun2. Solar cells use sun energy to generate small

electrical energy to power calculators.3. Solar panels use sun energy to generate heat

energy to heat water at home.

1. High speed wind can be used to turn the bladesof large windmills which will in turn drivegenerators to produce electricity.

90


31/36

Describe thetransmission

of electricity

Electrical energy is transmitted from power stationto the consumer using long transmission cables or

power lines. Electrical energy is transmitted at a high voltage and

use alternating current.

A step-up transformer which increases the voltageto as high as 110,000 or 132, 000 V.

Step-down transformers are used to decrease thevoltage before being delivered to the consumers.

The long tick cables used as transmission lines aremade of copper or aluminium

Describe theenergy lossin electricitytransmissioncablesdeduce theadvantage ofhigh voltagetransmission

The heating effect due to the resistance of the cablescauses loss of electrical energy as heat energy.

When a current flows in a cable, the power loss, Pthrough heating is P = I

2R where R is the

resistance of the cable.

The power loss can be reduced by(a) reducing the resistance of the cables(b) reducing the current in the cables

In order to reduce resistance of the cables, a thickcable is used eg copper or aluminium. But thickcables are very expensive to install and will be tooheavy to be supported securely.

The loss of power in the transmissions of electricity isreduced by reducing the current in the cables.

The power to be transmitted by the cables isP = VI where I= current in the cables,

V = voltage of the cables.

The current in the cables: V

PI =

This means that the current in the cables is inversely

proportional to the voltage of the cables for a certainvalue of power transmission.

When power is transmitted at lower voltage, thecurrent in the cables is large.

The greater the current in the cables, the greater thepower loss.

91


32/36

92

Activity 1: Solve problems involving electricity transmission

1. Find the power loss in atransmission cable when20 kW is transmitted

through a cable of 1.5

(i) at a voltage of 200 V(ii) at a voltage of 10 kV.

What is the effect of theenergy losses in case (i)and (ii)?

2. Electric power istransmitted from a powerstation to a town by atransmission cables with atotal resistance of 50 . Ifthe power stationgenerates 8 MW of power,calculate the power loss inthe cables if power is

transmitted(a) at 80 kV(b) at 400 kV

What is theNationalGridNetwork

National Grid Network is a network system of highvoltages cables which connects all the power stationsin the country to the consumers.

Electricity is generated at 25 kV at the power station. Itis then stepped up in a transformer to 132 kV before itis sent to the grid network.

The purpose of increasing the voltage to 132 kV is tolower the current flowing through the grid, and thisreducing power loss during transmission.

The high voltage in the grid is subsequently reduced bysub station transformers for distribution to local users.

Heavy industries will be supplied with power at 33 kV.Light industries will be supplied with power at 11 kV.


33/36

State theimportance

of theNationalGridNetwork

Offices will be supplied with power at 415 V whiledomestic users will be supplied with power at 240 V.

Cost of generation of electricity is reduced becausehigh voltage transmission reduces the current flowingthrough the cables and hence reduces power loss in

the cables. Power stations in areas where the demand is low can

supply electricity to areas where the demand is high.

If a particular station breaks down or is shut down formaintenance work, the other stations can supplyelectrical energy to the affected area.

The grid network also enables less efficient stations tobe shut down at off-peak period, thereby reducing theoverall cost of generation and transmission.

Power stations can be located outside city limits sothat air and environmental pollution can be reduced.

Transmission issues

Alternatingcurrent, a.c

An alternating current is used in thetransmission of electrical energy at a highvoltage because its voltage can be easilyincreased or decreased with transformers.

A transformer cannot function with a directcurrent.

High voltage orlow voltage?

Electrical power is transmitted at a high voltageso that

The current in the cables is smaller The loss of power due to heating of the cables

is minimized.

93


34/36

94

Overhead orunderground?

High voltage cables are the cheapest way ofsending power over long distances.

However, to prevent sparking, the only effectiveway of insulating the cables is to keep huge air

spaces around them The cable have to be suspended from pylons.

Cost of cables Copper cables have low resistance but are ofhigh cost

Aluminium cables are usually used as they arelight, have low resistance and cost less.

Charge leakagebetween thecables and theearth

To prevent charge leakage, the aluminiumcables are supported by high metal pylons.

The metal support of the pylon is earthed sothat it is safe to workers and the public whocome into contact with them.

Danger of beingstruck bylightning

The pylons carry lightning conductors that areproperly fixed into the ground

The cables are properly fixed with porcelainsupport so that the cables do not touch thepylons.

Danger of beingstruck by lightaircraft

Lights and special markers must be attached tothe pylons.

Theft Stricter laws should be enforced to deterthieves from stealing the aluminium cables.

Explain theimportanceofrenewableenergy

Non-renewable sources of energy such as crude oil,coal and natural gases are fast depleting. Alternativesmust be found to replace such sources to ensurecontinuous supply of power in the future.

Renewable energy sources are those which originatefrom the sun or the earth and will last as long as theSolar System itself.

From the sun: solar panels, solar cells, biomass, windand wave energy, hydroelectric power

From the earth: geothermal energy, energy from thetides.

Renewable sources of energy do not pollute theenvironment.


35/36

95

For renewable sources of energy to be widely used,many hurdles must be overcomed, especially thoserelated to the economical production and distributionof power generated from such sources.

Explain the effects on the environment caused by the use of varioussources to generate electricity.

Energyresource

Advantages Disadvantages

Hydro Renewable energy Water is freely available

in large quantities

Clean and does notpollute the environment

Water stored in damscan be used to irrigatefarms

Dams can be used tocontrol floods

Dams can be promotedas recreational centre

Building of dams canupset the balance of the

ecosystem

Not suitable in areaswhere natural disasterssuch as earthquakesmay occur

Not suitable in flat anddry regions.

Oil andnaturalgas

At present it is stillavailable in largequantities

Can be transported tothe location where it isto be used

Non-renewable energy Discharges harmful

gases that can pollutethe environment

High costSolar Renewable energy

Freely available Clean and no pollution

Requires very largespace to collect

sufficient energy Lower efficiency in the

generation of electricity

Intensity of sunlight isdependent of seasonalchanges, climate andlatitude of the region.

High cost


36/36

96

Coal Plenty of resourcesavailable for up to 200years

Can be transported tothe location where it isto be used

Non-renewable energy Discharges harmful

gases that can pollutethe environment

Nuclear A small amount uraniumcan release a largequantity of energy

Minimum discharge ofcarbon dioxide

Reactor in nuclearpower stations can beused to produce usefulradioisotopes to beused in industry,medicine andagriculture

High cost of building Waste in the form of

used fuel rods which arevery hot and highlyradioactive

Hot water dischargedcauses thermalpollution to theenvironment

Risk of accidents whichmay lead to the leakageof large amounts ofradioactive substancesto the environment.

Biomass Renewable energy Reduces problem of

disposal of organic

waste

Requires large storagespace far from humanpopulation if the

biomass is animal dungor sewage.

Wind Renewable energy Clean and does not

pollute environment

Requires manywindmills which cover alarger area

Generates high level ofnoise

1026899 Nota Padat Fizik F5 Electromagnet

Documents

Transcript of 1026899 Nota Padat Fizik F5 Electromagnet