Motors and Generators

OUtline faradays discovery of the genration of an EMF by moving a magnetic

* Faraday conducted an experiment to demonstrate electromagnetic induction using 2 coils rrappe around a soft iron ring. Primary connected to DC whilst secondary connected to galvanomer * When switched for DC turned on = current increased in primary coil = produced B field wiht increasing strength around iron ring * Increase in B field strength = induced EMF or current in secondary coil (F law) indicated by value on galvanomter * When current reached max value and become constant, strength of B field constant = no EMF or current in the galvanomer * When switch to DC turned off = current in primary coil decreased = decreasing B field strength around iron ring * Decreasing B field strength induced EMF or current in S coil (F Law) in opposite direction indicated by galvanomer

Why are electromagnets used over permanent magnets

* can change the direction fo the amgnetic field and therefore change the direction of the coil * can control the strength of the magnetic field depedning on the current, therefore a stronger magnetic ield an be produced to have greater toruqe * can be turned on or off and adjusted

Describe the 3 ways in which an EMF can be indcued Describe Faraday's experiemtn

1. the relative motoin betwene a magnet and coil 2. a change in magnetic field strength * Faraday conducted an experiment to demonstrate electromagnetic induction using 2 coils rrappe around a soft iron ring. Primary connected to DC whilst secondary connected to galvanomer * When switched for DC turned on = current increased in primary coil = produced B field wiht increasing strength around iron ring * Increase in B field strength = induced EMF or current in secondary coil (F law) indicated by value on galvanomter * When current reached max value and become constant, strength of B field constant = no EMF or current in the galvanomer * When switch to DC turned off = current in primary coil decreased = decreasing B field strength around iron ring * Decreasing B field strength induced EMF or current in S coil (F Law) in opposite direction indicated by galvanomer 3. striaght conductors moving in a uniform magnetic field cuts magnetic flux lines which also induces an EMF ε = Blvsinθ

Describe how eddy currents cause a braking effect in swinging copper plates

A braing effect can be observed when a copper plate moves thorugh external magnetic field due to the producetion of eddy currents which oppose the original change in flux Therefore it will slow down quicker than normal When the copper palte enters the external magnetic field, ther will be an increase in magnetic flux and a RELATIVE MOTIN BETWEEN THE PLATE AND THE EX MF, and cause a change in magnetic flux. This will induce eddy current in the copper plate due to Faraday's law The current will be in a direction that produces a MF that opposes teh original change in magnetic flux due to Lenz's law The interaction between the magnetic fields will result in a force due to the motor effeect, and will be a braking force that opposes the motion of the copper plate. This means it will slow down When it is completely isnide the plate, there is no change in magnetic flux and therefore will not change speed When it leaves the magnetic field, there will be a decrease in flux/relative motin between the plate and field. This means it will induce the eddy currents again due to fara law, which is in a direction that produces a magnetic field that opposes the oirignal change in flux due to Lenz's law, which is the opposite direction from before. This will cause a braking effect that makes it further slow down

Describe the application of the motor effect on the galvanometer

A current which is measured, is passed through a coil from an external circuit and thus induces a magnetic field This MF interacts witht he external MF provided by the radial permanent magnets, and thus produces a force on the coil = exerts a torque which causes it to rotate around the pivot AKA THE MOTOR EFFECT this causes the needle to move along the linear scale and the spring to tigether = provides a restoring torque that opposes the torque of the coil When the restorign torque = torque on coil = needle comes to rest on linear scale thus this provides a calibrated reading that corresponds to the current being measured. The large the current, the greatehr the toruqe, and the further the torque will rotate and give a larger reading

How does Lenz's law take into considering the conservation of energy

Consider the reverse scenrario where the induced EMF was in a direction that intensified the original change in magnetic flux This will increase the change in magnetic flux and the induced EMF which creates more energy without doing more work, and thus violate the Law of Conervation of energy

How does a galvanomer work (desribe comoponents as wel)

A device which measures small currents through the mechanical motoin of an induction coil and the motor effect COILS * the coils are supplied with the current that is to be measured from an external cirucit. This will induce a magnetic field which intearcts with the external magnetic field from the radial magnets, thus produce a force and torque on the coil due to the motor effect. It only turns to a certain angle depending on the magnitude of the current which passes through it SPRING * the spring provides the restoring torque which opposes the motion of th torque from the coil, allowing the needle to come to rest and provide a calibrated reading PERMANENT RADIAL MAGNETS * provid the external amgnetic field which interacts with teh magnetic field from the coils and therefore helps to produce the toruqe and force from the motor effect * the radial magnets ensure that the plane of the coils are parallel to the direction of the magnetic field, maximising the toruqe * this also means that a linear scale can be used, as the angle of diflection of the needle is only dependent on the magnitude of the current and not the orientation of the coil i.e. the θ * this means that torque, curretna and angle of deflection are all in proportion NEEDLE * provides the reading on the linear scale of the size and deflection of current LINEAR SCALE * alllows size and direction of the current to be deterimned with the same sized division SOFT IRON CORE intensifies the strength of the external and the induced magnetic field which HOW IT WORKS * the coils are supplied with the curet form the external circuit. This induces a magntic field which inteacts with teh external magnetic field and thusproduces a force and a torque on the coil, making it move around the pivot by the motor effect * the coil starts to turn and as it turns the spring will tighten, providing teh restoring torque which opposes the torque of the coil. This makes the needle move along the linear scale * the angle fo deflection is dependent on the magnitude of the current * when the restoring torque is equal to the torque of the coil, the needle comes to rest and provides a calibrated reading of the direction and size of the current * the larger the current the greater the angle of deflection

What is a generator and what scientific principles does it use? What are its components?

A generator uses rotaional kinetic energy and converts it to electrical energy i.e. the opposite function of a motor As the rotor is being turned in the magnetic field, this creates a chagne in magnetic flux which induces an EMF and then a current in the coils due to Faraday's law. The current is in a direction so that it opposes the original change in flux due to Lenz's Law COMPONENTS 1. Stator - consists of permanent bar magnets or an electromagnet (wounds of coil wrapped around a soft iron core). It provides the magnetic field so that when the rotor is turned, it will cause a change in magnetic flux which induce an EMF and current in the plane of the coils due to Faraday's law 2. Rotor - consists of loops of coils wrapped around the armature. Teh armature is the laminated iron core mounted on an axle - torque is applied ot the axle which makes the rotor spin, experiencing a change in magnetic flux. This induces an EMf and then a current - usually more than one set of coils is used (usually 3) which are offset at 120 degrees to produce a steady output of (DC generator) or 3 phase AC output - industrially, normally the rotor is the stator and the stator is the rotor -- this is becasue as more coils are used, it becomes ineffective to apply torque to a large about of coils - a laminated iron core intensifies the strength of both the induced and external magnetic field to maximise the current induced - the heat loss is minimised by the laminations because it reduces the size of the eddy currents 3. Split ring commutator (DC) - consists of 2 semi circular metal rings which reverse the direction of the curernt every half turn sot hat the output curernt has one continous direction - for a DC generator with multiple coils, it has multi part commutator with even number of bars cnnected to the coils 4. Slip rings commutator (AC) - consists fo 2 circular metla rings which maintain the electrical contact between the ends of the coil to the external circuit. They have a continous flow of current so that the output current flips direction every half turn and thus craets an alternating current 5. Brushes - 2 graphite blocks which maintain electrical contact wbeten the commutatos and the external circuit - they wear away over time thus they requrie maintenance to allow for efficient generation of electricity 6. the external circuit -- where teh output current flows external rotational force is required as the kinetic input energy to creat a change in flux and thus generate an EMF

What is a motor and describe the compoentns of the DC motor

A motor uses electrical energy and converts it to kinetic energy COMPONETNS STATOR Conssits of the permanent magents or electromagnets (coisl wrapped around a soft iron core) which provide the external magnetic field which interacts with the magnetic field from the rotor to thus produce a net force and torque onto the coil due to the motor effect * to maximise torque, raidal magnets are used as it ensures that the angle between the plane to the plane of the coil andt eh magnetic field is 180 degrees ROTOR * consists of loops of coil wrapped around the armature. Teh armature is a laminated iron core mounted on an axle. It is provides with teh electiricty DC and produces a magnetic field which interacts with teh external magnetic field and therefore * the laminated iron core is used to minimise heat loss by reducing the size of the eddy current * usually more than one set of coils are used to maximise the torque (3 set of coils 120 degrees offset) * soft iron core used to intensify the magnetic field strength of both the induced and the external * axle provides the axle of rotation for the rotor SPLIT RING COMMUTATOR * consists of 2 semi cirular metal rings which reverse the direction of the current every half turn, to ensure a consistent direction of torque * for a DC motor with multiple coils, a multipart commutator with an even number of bars are connected to the coils BRUSHES * the busehs are 2 graphite blocks which ensure electircal contact wtih teh external circuit and the rotor * the brushes wear away over time, thus must be replaced to maintain efficiency DC SUPPLY * provides teh DC current to teh rotorr

Describe the ways of EMF generation

A straight conductor moving in a uniform field, which will cut magnetic flux lines to induce an EMF ε =Blvsinθ OR A change in magnetic flux through: - changing the magnetic field strength - relative motion between the magnet and the coil - a change of the perpendicular area of the coil Which will induce an EMF or current in a complete circuit, which is directly proportional to the rate of change of magnetic flux through the coil. Therefore a magnet with a relatively high velocity will create a larger EMF Formula: ε=-nΔφ/Δt ε(V) = induced EMF n = number of could

Describe the purpose of transformers in electrical circuit i.e. what is it and how does it work

A transformer is used to step up or step down the voltage to step down or step up the AC current respectively, through using the principle of electromagnetic induction - the AC current is supplied to the primary coil, which generates a changing magnetic field which is amplified/intensified by the soft iron core - the changing in magnetic flux threads through to the secondary coil, and induces an EMF or current due to Faraday's Law - the AC current is in a direction so that it opposes the original change in flux i.e. it is in the opposite direction of the current in the primary coil. - the output current has the same frequency as the input current, and transformers can only be used with AC not DC

Discuss the impact of development of transformers in society

ADVANTAGES 1. Allowed for electricity to be accessed by more people over larger distances - transformers could be used to step up or step down the voltage to step down or to step up teh curent repsectively and tehrefore minimises power loss - This allowed power stations to be of service to multiple centres — allows people in remote areas to access electricity from one power station - the minimal poewr loss means more efficiency and affordabiliyt, and thus could be accessed by people in remote areas and therefore improve their quality of lfie 2. Minimal poewr loss -- meant more efficiency and cost effectivieness -- greater affordabiilty for more people 3. More applinces could be developed - because transformers can be used to change voltages, it meant that appliances which rqruied lower voltages could be used - e.g. phones, laptops, lighting, air con (many hoem appliances) requried a lower voltage. In havign the transformer these thigns coiuld be used and therefore improve quality of life 4. More aestheitlcaly pleasing because less cables requried for different voltages DISADVANTGES 1. increased automation meant loss of employment opportunities for unskilled labour 2. increased use fo fossil fuels - non renewable - the increased use of fossil fuels meant more detrimental to environment - depletes teh non renewable resource which must also be used in society eg. plastics, fertilisers - it releases CO2 whci is a greenhosue gas -- lead to rise in ocean levels, which is bad for aquatic life - releases SO2 which contributes to acid rain -- acidification of the ocean, changing pH detrimental to organisms as well - heat pollution from coollant towers can change termpatrue in oceans = less oxygen dissolved = difficult for fish to breathe 3.The increased dependence on electricity will be problematic when power supply is disrupted 4. health risk from greater chance of electrocution

Explain that in electric motors, back EMF opposes the supply EMF and the diferrent scenarios

As the coil rotates, this creates a change in magnetic flux thus there is an EMF induced called a back EMF which opposes teh supply EMF εnet = εsupply - εback Initlally the coil is stationary and the current flowing through it is at maximum i.e. the current is the supply current. HOwever this maximum current doesn't last long and the coil starts to rotate due to the motor effect. As the coil starts toe rotae this is a change in magnetic flux thus it will induce an EMF due to faradays law and it will oppose the supply current due to Lenz laws. As the coil starts to rotate due to the toruqe (torque is acceleraion as it is dependent on force) the back EMF increases therefore reducing the supply emf. this is because ε=Δφ/Δt. As the net EMF decreases this means the toruqe is making it accelerate less and less. When the Back EMF is almost equal to the supply EMF the rotation of the coil is at maximum. There is a little net EMF left because the frictional forces prevent eh back EMF ffrom equaling the supply EMF

Explain why voltage transformations are relate to the conservation of energy

Assuming that the transformer is 100 percent efficient, then the poewr input should equal to the power output due to the conservation of energy i.e. Pp = Ps IpVp = IsVs Vp/Vs = Is/Ip = Np/Ns

How can magnetic flux be changed

B FIELD CAN BE CHANGED BY: electromagnet with changing current through it or the relative motoin between the magnet and the coil AREA CAN BE CHANGED BY size, shape and angle

Describe the components of a galvanomter

COILS - where the current from an extenernal circuit is passed through (it is also measured) to induce a magnetic field - this interacts with the external MF and thus provides torque via the motor effect SOFT IRON CORE - strengths the external magnetic field and induced magnetic field to provide maximise torque - this increases the sensitivity of the galvanometer RADIAL PERMAMNENT MAGNETS - provides the external MF that interacts with induced MF to produce a force and thus a torque via he motor effect - parallel to the plane of the coil as it rotates so the linear scale can be used - the angle of deflection is proportional to the current and torque flowing through the coil SPRINGS - provides the restoring torque that opposes the turning torque of the coil to prevent rotation - allows the needle to come to rest NEEDLE - moves along linear scale to indicate the amount of deflection and size of current LINEAR SCALE - allows size and direction of the current to measured with same size division > linear sclae needed to angle turned by needle is directlyproportional to the current = turnign torque depends on the magnitude of the cucrent and independent of oriengtatino of θ of coil from radial MF

Describe the difference btween AC and DC generator

COMMUTATOR - the AC generator has slip rings commutator to maintain electrical contact between the ends of the coil andt eh external circuit whereas the DC generator has the split ring commutator to reverse the direction of the current every half turn to ensure a continous flow of current inthe output WHERE IS VARIES WITH ONE COIL - because the DC generator has one continous output, it varies between 0 and maximum - for AC generator, becasue the direction of the current reverses every half turn, it varies between minimum and maximum sinusoidally MULTIPLE COILS - for a DC generator, when it has multiple coils (3 offset coils 120 degrees) and a multipart commutator it produces an output with a relatively steady voltage - for AC generator, when it has multiple coils offset at 120 degrees, the output produces a multi-phase voltage i.e. 3 phase AC GRAPH (LOOk at notes)

HOw does a loudspeaker work

COMPONENTS Using electrical energy and converts it to sound energy through using the motor effect Voice coils * provides with the AC current which induces a amgnetic field which intearcts witht eh external magnetic field and thus produces a force onto the coils by motor effect which vibrates teh paper cone attached --> vibrates osund particles Paper cone * attached to the coils which move in and out due to the motor effect, vibrating the paper cone which thus makes it vibrate the surroudning sound particlse and produce sound enrgy AC current * the frequency and amplitude of the AC current affects the pitch and loudness of the sound Circular permanent magnets * provides teh radial magnetic field (has an outer circle ring pole and a central pole) HOW IT WORKS * AC signal is supplied to the voice coil which induces a magnetic field that interacts with the external magnetic field provided by the permanent circular magnet * This results in a force on the coil in the direction given by RH palm rule due to the motor effect, pushing coil and attached paper cone in and out. Because the force varies in size and direction depending on the current, it will vibrate in and out in different amplitudes * This vibrates surrounding air particles which produces sound energy * The pitch and volume of the sound is determined by the frequency and amplitude of the AC signal supplied respectively

What does a galvanometer do

Device used to measure a small current thr huh the mechanical movement of a coil aka motor effect

How are eddy currents produced

Eddy currents are produced in a solid, flat top conductor, wehre a change in magnetic field induces small circular currents due to faradays law, in a direciton that produces a magnetic field which opposes the original change in flux

Gather secondary information to identify how eddy currents have been utilised in electromagnetic braking

Electromagnetic braking is uses the opposing force created from the production of eddy currents in order to slow the train down HOW IT WORKS Electromagnets with alternating poles are suspended above the rails. Alternaitng so that when the eddy currents are induced they combine instead of cancel out When the train moves, it creates a Δφ which indcues eddy currents in the wheels in a direction which opposes the original change in flux (F and L law). It will interact with teh exteranl amgnetic field and produce an opposing force on the train accordin gto the motor effect. The braking force is proportional to the speed of the trian, becasue the faster the train the graeter the rate of the change of flux and therefore a greater braking force. THis is also related to the conservation of energy as the trains kinetic enery is converted into making eddy currents. The rest of the energy is lost thorugh reistive heating and magnetic hysteresis ADVANTAGES * smooth braking -- becasue the speed of the train and braking force are directly proportionate, t allows the train to come to a smooth stop as there is less force as teh train slows down even more * less maintenance because there is no direct contact ebtween rails and wheels = less wear and tear Dis * weak braking force -- because the braking force isnt as storng as the conventional brake pad systems, can't have emergency/rapid stops * rail heating -- from reisstive heating, the rails msut be able to withstand high temperatures

Discuss the energy losses that occur as energy is fed through transmission lines from the generator to the consumer and how to minimise them Write all the formulas

Energy losses occur along transmision lines through resistive heating, coronas and induction of eddy currents in nearby metal objects P=IV (only in or out) Ploss = I^2R P=E/t Pin = Pout + Ploss RESISTIVE HEATING - this occurs when the electorns in the current collide with the nuclei of the atoms in the metal lattice, releasing heat energy R = ρl/A to minimise: - use transformers to step up the votlage which steps downt eh curren and therefore less power loss as Ploss = I^2R - have wires with large cross sectional area (but this is qutie expensive) - shorter length of wire - a material with lower resistivity CORONAS - usually aluminium cables are used for transmision as they are lighter and cheaper than copper - to increase their strength they are usually wrapped around a core of galvanised steel. However if the diamater of the conductor is not big enough, then it can cause a large electrical field which could ionise the atoms in the surrounding air near the surface of the wire, therefore producing a corona. This can cause interference with the radio and TV signals, and also is another cause of power loss - to minimise this issue, bundles of conductors are used in whcih each phase wire has a bundle of 2-4 conductors seaprated by spaces. This reduces teh strength of the electrical field surorunding teh wires so reduces the corona effect. Weights are also used to reduce unwatned vibrations INDUCTION OF EDDY CURRENTS - the changing magnetic flux from the AC current can induce eddy currents in the soft iron core To minimise this issue, laminated iron cores i.e. thin layers of insulative materials in the direction parallel to the magnetic field is used to reduce the size of teh eddy current as there is less surface area - insulative material are used to suspend transmission lines away from the metal towers

Gather, process and analyse information to identify some of the energy transfers and transformation involving the conversion of electrical energy into mroe useful forms in the one and industry

Energy transfer occurs when energy moves form one object or locatino to another in the same form Home -- energy from heating element in a kettle boils water Industry -- heat of combustion form heating element melts metals Energy transformation occurs when energy is changed from one form to anotehr within .a appliance Home -- electrical energy into heat energy for a toaster, electrcal energy to light energy in a bulb, electrical energy . to EM radiation in microwaves, electrical energy to kinetic energy in blenders and fans Industriy -- electrical energy to kinetic in motors, electrical energy to x ray in imaging machinery, electrical energy to chemical energy in electrolysis

Identify the relationship between the ratio of the number of turns primary and secondary coils and the ratio of primary to secondary voltage Solve problems and analyse information about transformers using formula

Equating: Vp = -nΔφ/Δτ and Vs =-nΔφ/Δτ you get Vp/Vs = Np/Ns

What is the formula for the force of the external MF and what are the facotrs that affect the strength of the force of the MF

F = BIlsinθ strength of B field length current the size of acute angle

θ

F = BIlsinθ where θ is the angle between the straught current carrying conductor and the MF τ = Fdcosθ = nBIAcosθ where in the first quesiton, theta is the angle between the direction of the force and the perpendicular force, and in the second equation, θ is the angle between the plane of the coil and the MF

What is faradays law and identify the ways it can occur

Faraday's law states that a change in magnetic flux will induce an EMF (voltage) in a conductor or a current in a complete circuit This change in magnetic flux can occur through the relative motion of a magnet to a coil, or through a change in the strength of a magnetic field

What is the lever arm

The perpendicular distance between where the force is applied and the pivot of the rotataiton of the object

Explain how an induction cooktop works AND PROS and cons

INDUCTION COOKTOP Induction cooktops based on electrical ranges converts the electrical energy from eddy currents into heat energy in ferromagnetic pans to heat the food HOW IT WORKS A high frequency AC current is supplied to the induction coils to produce a rapidly oscillating magnetic field from the current moving back and forth This will result in a change of magnetic flux and induce eddy currents at the base of the ferromagnetic pans from Fara Laws, which will be in a direction that opposes the original change in magnetic flux The ferromagnetic material of the pan will convert the electrical eddy current energy into heat energy through resistive heating, where Ploss = I^2R Resistive heating: When the electrons of teh eddy currents collide with the nuclei of the atoms in the metal lattice and produce heat energy to heat the food Reqiures ferromagnetic metals e.g. iron and steele to conduct magnetic flux, increasing induced eddy current quired for resistive ehating ADVANTGES > mroe energy efficient as the electrical energy is converted to heat with no energy loss to the environment or heating the stovetop > faster heating > Safer to use as there is no heat remianing on the stove top DIS > more expensive than the conventional cook top > can only work with ferromagnetic materail as it must conduct the changing magnetic flux to produce the eddy current/electrical energy into heat energy > other nearby objects may heat up espeically ferromagnetic substances

Describe the 2 ways induction occurs

INDUCTION VIA THE RELATIVE MOTION BETWEEN MAGNET AND COIL When a bar magnet is move into a conducting coil (connected to a galvanometer in series) a current was induced When it was stationary relative to the conducting coil, no current When the bar magneti moved out from the conducting coil, the current was induced in the opposite direction INDUCTION VIA THE CHANGE OF STRENGTH OF MF When the DC power supply is turned on, an increasnig current ran through the primary coil which generated a magnetic fiedl around the iron ring which strengthened/increased the MF strength This creates a change in magneitc flux and thus induced a EMF or current in the secondary coil, indicated by the value on the galvanometer When the current was maximised and was constant, this created no EMF or induced current in the galvanomer as the magnetic field was constatn When the DC power supply was turned off, this created a decreasing current in the pirimary coil, which decreased the strength of the MF strength around the ring, and this induced an EMF or current in the secondary coil in the opposite direction as indicated by the galvanometer

Gather and analyse information identify how transmission liens are insulated from supporting structures and protected from lightning strikes

INSULATION OF TRANSMISSION WIRES Transmission wires msut be insulted to prevent current leakage and sparking between transmission lines and the tower - ceramic/glass insulators are used to insulate the wires. They consist of ceramic discs joined together. These ceramic discs are curved at the top to prevent dust and grime from collecting which could create a conductive path when wet, and rippled corrugations which could increase the distance the current had to travel - these materials are relatively strong, cheap and readily avilabile. They msut be strong to hold the weight of the conductor, and must be able to withstand not only the normal voltages in which they carry, but also large voltages when lightning strikes - the design of the transmission lines. they msut be apart enough so that there is no sparking between them caused by wind or the force of attraction between parallel wires. - a common deisgn is the v string support, where teh conductors are 90 degrees from each other which prevents swinging in the crosswind and reduction to the structure's size LIGHTNING STRIKES - since transmission lines and towers are high above the ground, they are very susceptible to lightning strikes. This can cause current surges in the wire, which can lead into the transformer and therefore damage equipment 1. using shield wires -- they are located above the transmission lines and they are non current carrying wires connected to earth cables. When lightning strikes, the current is redirected into the ground to prevent the surge 2. earth cables are used to redirect the lightning to the ground from the shield wires and therefore prevent a surge 3. metal towers are well earthed to the ground which can act and earth protection against lightnign 4. distance btween towers is at least 150 metres so when lightning strikes one tower, the adjacent tower wont be affected

Discuss why some electrical appliances in the home that are connected to the mains domestic power supply use a transformer

In Australia the main domestic supply is 240V whilst the industrial supply is three phase 415V AC electricity. However most appliances at home do not requrie 240V for sfafe and efficient operation. Hence transformers are use to step up or to step down the voltage required in electrical appliances LOWER THAN 240V - most appliances in the home require a voltage lower than 240 e.g. phones and laptops i.e. appliances requiring batteries - most of these appliances also need an AC to DC convertor called a rectifier in order to charge, becasue if they need DC supply to charge otherwise it woudl charge then immediately discharge HIGHER THAN 240 - very few appliances require higher than 240V, as it is normally used to industrial purposes - old conventional TV required a voltage higher than 240 to drive the electron gun of the cathode tube

Analyse secondary information on the competition between Westinghouse and Edison to supply electricity to cities

In the 19th centruy Edison favoured DC whilst Westinghouse favoured AC, which led to competition - intially DC was favoured because technolgoy for it was well established and ti worked well over short distances - however DC was distributed at the voltages in whihc it had to be used, which meant it was not as cost effective and inefficent becasue this led to large power losses. Therefore it could be used over large distances. This led to many power stations and transmission lines which was unaesthetially appealing - AC however could be used with transformder thus overcoming these issues because there was less poewr loss. It could supply a large range of voltages and it was more costly and eneryg efficient - Tesla's invention of the AC indcution motor led to Westinghouse supporting this new method fo electricty generation - Edison owned all the power stations and inventions using DC so he sought to prove AC was dangerous by electrocuting animals and convincing authorities to use it in electirc chair. He even resorted to legal disputes to have AC banned - However in 1891 Westinghouse secured a contract to generate hydroelectricity at Niagara fall, and supplied NYC with 10 generators in 1896, ending the dispute

What is generated potential difference

The rate of change of magnetic flux through a circuit

Describe back EMF in terms of Lenz's law in motors

The relative motion between the rotation of the coils and the external magnetic field induces an EMF and current through the coils due to Faradays law The direction fo the back EMF will be so that it opposes the original change in magnetic flux aka back emf (Lenz's law)

Analyse the competition between Westinghouse and Eddison

In the late 19th century, Edison favoured the DC supply whilst Westinghous favoured AC supply which led to competition > originally DC supply was favoured becasue the technology for the application using DC was well established and it worked well > because DC supply could not be worked with transformers, it had be distributed at the voltage used in the hosueholds > however using DC supply led to large amount of power loss and thus less efficiency during transmission ebcasue transformers could not be sued and therefore limited the distance in which it could be transmitted > this also led to many power stations and large amount of wires which was less aesthetically pleasing for society > AC could be used with transformers, allowing voltages to be stepped up to reduce power loss and could be transmitted over large distances > this allowed fewer power stations and wires to be used and could supply a range of voltage requriements > Tesla's invention of the induction motor which used AC e supple led to support on Westinghouse's AC supply > Edison was the owner of power statiosn and invnetions using DC technology, thus he attempted to prove AC was dangerous by electrocuting animals in pulbic and convinced the authorities to use it in electric chairs. He also resorted to legal disputes in order to have AC abnned > however in 1891, when Westinghouse secured a contract to generate hydroelectricity at Niagara falls and supplied all of NYC with 10 generators (in 1896), AC wa adopted as the standard to supply electricity, therefore ending the dispute

Gather, analyse and present information to explain how induction is used in cooktops in electric ranges. INDUCTION COOKTOPS

Induction cooktops in electric ranges use an oscilating magneitc field to induce eddy currents in the base of a ferromagnetic pan, so that it can cause resistive heating which heats up the foot HOW IT WORKS An AC current is supplied to an induction coil which creates an oscilating magnetic field The oscilating magnetic field will create a change in flux, therefore inducing eddy currents by Faraday's law in the base of the ferromagnetic pan. The eddy currents will cause resistive heating due oto the high resistance in the pan, as the electrons collide with the nuclei of the metal lattice in the base of the pan, thus causing the electrical energy to be converted to heat i.e. resistive heating where Ploss=I^2R. ADVANTGES AND DISADVANTAGS * efficient heating becasue all the electrical anergy is converted to heat without any losses to the environment * safe because no leat is left behind * fast heating -- faster than conventional * only ferromagnetic materials can be used becasue it msut be able to conduct magnetic flux (iron and steel can be used, aluminium cannot) * expensive * nearby ferromagnetic objects may heat up which is dangerous

How to maximise torque in DC motor

Iron core int he electromagnet More coils offset at 120 degrees More loops A curved bar magnet

Assess the effects of the development of AC generators on society and the environment

Judgement statement: AC generators ahve positively affected society but negatively affected teh environemnt, and has led to widespread use fo AC electricity SOCIETY * en engines with electrical engines * More efficient therefore more cost effective. More efficient from the transformers which reduce power loss * More efficient production because of more efficient machinery in factories = cheaper to produce and therefore economically viable * Clean energy — hydroelectricity schemes and wind turbines * Provided work for many people, took pressure off government welfare and cheaper electricity * Easier access to electricity * Transformers can be used to reduce power loss (formula) * This allows AC electricity to be transmitted across large distances, increasing accessibility in remote areas * Increased automation leading more efficient, affordable and reliable products * This improves quality of life because it allows for air conditioning, refrigeration, lighting, revolutionised communication, movies, TV etc for many people * New appliaciances e.g. computer revolution, which require a reliable source of electricity impacted everybody and everything we do for leisure and work e.g. baking, buying and selling etc Disadvantages * Led to loss of unskilled labour and increase unemployment * Widespread use of AC electricity increased risk of electrocution * Increased dependence on electricity will be problematic when power supply is disrupted ENVIRONMENT Advantages: by changing from steam to electricity, it means less fuel wastes, less air pollutants and cleaner air. BY having them located away from the city it means cleaner air, because they are able to have that longer transmisison Disadvantegs * Burning fossil fuels to generator AC electricity has increased levels of air pollution, greenhouse gases, global warming and acid rain * Greenhouse gases lad to climate change = sea level rise, acidification of oceans, cylones etc * Heat pollution from coolant water at power stations go into natural streams which affects water quality and organism diversity, low oxygen levels * The development of nuclear power stations to cope with decreasing availability fo fossil fuels has led to nuclear waste detrimental to the environment * Some electricity generated from hydroelectricity and wind turbines has led to killing of birds and bats * Construction of transmission lines and generators destroyed natural habitats OVERALL The advantages of the development of AC generators on society and the environment significantly outweighs the disadvantages, leading to the widespread use of AC electricity

What is lenz's law and how dos it take into account the conservation of energy

Lenz alw states taht eh induced curernt in a loop will be in a direction so that the magnetic field it generates opposes teh original cahgne in flux CONSERVATION OF ENERGY Lenz's law takes in the conservation of energy. Consider the reverse scenario where the current would be in a direction so that the mangetic field it generated was in the same direction as the original change in flux. The kinetic energy of the movement of th magnet to coil or vice versa is transformed into electrical. If the EMF was in a direction so that it intensified the orignal change in flux, then this owul lead to a greater chagne in flux and therefore greater electrical energy wihtout doing more work and thus violating the concept of the Law of Conservatin of Energy. Hence to uphold the LCE, the curent needs to be a direction so that it opposes teh orignal change in flux

What is magnetic flux

MF field lines

Compare magnetic field strength and magnetic flux. What is the formula

Magnetic field strength = number/density of the of magnetic field lines per unit of area. Measured in TEsla Magntic flux -- number of field lines in a given area φ = BAcosθ

What is magnetic flux and what is the formula

Magnetic flux is the number of field lines passing through a given area The formula: Φ=BA(perpendicular area) = BAsinθ Where φ is the magnetic flux in Wb Β= the magnetic field strength or magnetic flux density in T A= the perpendicular area to the magnetic field lines θ= the angle between the plane of the area and magnetic field lines

How to maximise toruque

More coils offset Radial magnets Soft iron core More coil loops

What is the motor effect (outcome definition, and then the understanding definition)

OUTCOME: The force exerted on a straight current carrying conductor from the external magnetic field, also known as the motor effect UNDERSTANDING When the magnetic field created by the SCC interacts with the exerternal magnetic field, a force is exerted onto the SCC also known as the motor effect. The direction is determined by the RH palm rule aka motor effect

What will a variable resistor do

Placed in the circuit to reduce the large current which would cause burn out

What is the formula for power efficiency

Pout/Pin *100

What is accuracy, reliability and validity and how can it be improved

RELIABILITY > repeated and consistent results > there might be a possibility of random error therefore affecting how consistent the results are. Average the results and then comparing the values with the avergae can determine how reliable the results are. The results are consistent if they are close to the averaged vlaue > repeating experiment helps identify the outliers and reduces the effect of random error > collecting quantitative data rather than qualitative more consistency due to objective rather than subjective intepretation > the line of best fit -- consistent results should be close to the line of best fit > look out for: outliers, how close to line fo ebst fit, averaged results, random errors, quantitatvie data, repeated ACCURACY > how close the measured values fall to the theoretical value > the data msut fall close to the line of best fit. If ti is far from the line of best fit then there msut be uncertainties > if the line of best fit doesn't pass through the origin then there migth be systematic error VALIDITY > if it answers the aim > ensure all variables are controlled except the independent. If not all variables are controlled, then there might be other factors affecting the dependent variable other than the independent variable. This means it won't answer the making and thus make the experiment invalid > if the experiemnt is inaccurate or unreliable, then it means teh results are wrong and thus means the aim is not answered. Therefore an improvement of reliability and accuracy can make it more valid becasue then it means it is closer to the expected results and answers the aim

Describe the main features of an induction motor and how it works

STATOR -- consists of 3 pairs of electromagnets with a soft iron core mounted on a cylindrical frame. Each pair of the coils is supplied with one of teh 3 phase AC currents, producing a rotating magnetic field as it moves as the pair of electrmagnet with the maximum changes ROTOR -- consists of copper or aluminium conducting bars which are attached to end rings, forming a squirrel cage. It is encased in a laminated armature with a soft iron core to concentrate the magnetic field, lamintiosn limit the eddy currents and axle for rotation HOW IT WORKS - the stator produces a rotating magnetic field and thus a change in magnetic flux as it moves threading the rotor - the relative motoin between the rotor and the stator induces an EMF in the rotor due to Faraday's law. It will be in a direction so that the magnetic field it generates will oppose teh roriginal change in flux due to Lenz's law. When the 2 magnetic fields interact, it produces a force and thus a net torque on the rotor due to the motor effect, causing it to rotate and 'follow' the stator - as the speed of the rotor increases, the relative motin between the rotor and the stator decreases and thus a smaller EMF and magnetic field. Because of this smaller magnetic field, the rotor can never reach the speed of the stator even at maximum due to the decreasing force. This speed is known as teh slip speed. It also can never be the stator speed because the rotor usually has a load on it that causes friction which makes it slow down. - this difference in speed is needed however because it allows for that relative motion between the stator and rotor which induces the EMF and current and therefore force * If it was the same speed as the rotating B field, there would be no change in flux and no torque, which would slow down due to friction * Note: AC induction motors do not require commutators or brushes and hence have fewer moving parts. This makes them lighter, more efficient and reliable compared to DC motors

Compare step up and step down transformers and where they are used

STEP UP - the voltage of the primary is less than the secondary - the current of the primary is more than the secondary - the number of turns in the primary is less than the secondary - Used at power stations to increase voltage and reduce current for long distance transmission, and also television sets to increase voltage to operate the picture tubeo STEP DOWN - the voltage of the primary is more than the secondary - the current of the primary is less than the secondary - the number of coil turns in the primary is more than the secondary - Used for cathode ray TVs, substations and in towns to reduce transmission line voltage for domestic and industrial use, and used in computers, radios, and CD players to reduce household electricity to very low voltages for electronic components

Compare the structure and function of a motor and a generator

STRUCTURE - they ahve the same structure i.e. stator, rotor, armature (laminated iron core, wounds of coil and axle), external circuit, brushes, commutator - back EMF in the motor is teh same as the EMF generated in a generator FUCNTION - they have reversed function i.e. the generator reqruies mechanical energy to create electrical energy, wehreas teh motor requries electrical energy to create mechanical energy - the input and the output is reversed -- the input of a motor is the external circuit and the output is teh rotating rotor, whereas the input of a genreator is the axle and teh output is the external circuit

What are the types of errors that affect accuracy and how can they be minimised

SYSTEMATIC ERROR > a consistent error that occurs even if the correct technique is used/consistent results. Cannot be improved by repeating and averaging. Makes experiment invalid > can be improved by using a calibrated machine, it reduces the zero error > well calibrated machine instead of human reaction time = increase accuracy as the human error is eliminaited RANDOM ERROR > an error that occurs even if correct technique, jsut small variable > can be improved by repeating and averagign the results. This is becasue averages are alwyas closer to the theoretical value and the line of best fit and eliminates any outliers > using an automated machine instead of human reaction time because eliminates any errors of the operator > More sig figs > correct technique TYPES > parallax error -- uncertainty of reading the scale due to position of eye relative to the machine. It is a type of random error and can be improved by repeating and averaing > zero error -- the deviation of the pointer to 0. It is a type of systematic error and can be improved by physically changing the machine so that the pointer is aligned at 0, or mathematiclaly, by noting down the amount it is deviated from the 0, and then subtracting it from all the results > the limits of the accuracy fo the machine -- someitmes teh machine is limited in how many sigfigs it can give. Improved by repeated and averaging as it is a type of random error > errors from the environment - can be systematic or random e.g. the air pressure or temperature chagne

What is a DC motor and what are the main features

The DC motor will convert electrical energy into rotational kinetic energy due to the motor effect, which allows the motor to rotate STATOR Role > provides the external MF which is able to interact with the MF from the current and thus produce a force due to the motor effect Features > consists of a permanent magnet or a electromagnetic with an iron core (coils connected to a power source to create MF). The iron core strengthens the MF and therefore the torque > Electromagnet benefits: produces a stronger MF and therefore a greater torque, the direction of the MF can be reversed by reversing the current and torque, and the strength of the MF can be adjusted/switch on or off > bar magnet: it maximises the torque by being curved to produce a radial MF that is parallel to the palne of the coil ROTOR Role: carries the current that interacts with the external MF to provide torque and thus rotation (laminated iron core, axle and coils Setup: > conssited of loops of coil wrapped around an armature, which is a laminated iron core mounted on an axle > laminated iron core intensifies the strength of external MF and induced one fro the current to maximise torque on the coil > laminations minimise heat loss by reducing size of eddy current > axle provides axis of rotation SPLIT RING COMMUTATOR Role: reverse the direciton of the current every half tyrn so the torque on the rotor is in the same direction Setup: > 2 semi circular metla rings > in DC motors, there are multiple coils, a multi part commutator has even number of bars connected to the coils BRUSHES Role: graphite blocks on the commutator which maintain electrical contact between the split ring commutator and the external circuit Wears away overtime due to freiction and requires replacement to maintain electric contact Graphite is used because: > it is a lubricant = reduces friction = more efficient motor and minimises wear and tear > can conduct electricity > can withstand high temperatures generated by friction ebtween the brushes and commutators DC SUPPLY > produce current in the coils which interact with external MF to produce torque and motor effect

Gather secondary information to discuss advantages/disadvantages of AC and DC generators and relate these to their use

The advantages and disadvantages of a DC and AC generator are dependent on: STRUCTURE, FUNCTION OF THE ROTOR AND THE STATOR, OUTPUT AND ABILITY TO BE USED WITH A TRANSFOMER AC: Advantages Structure: the slip rings commutator consists of circular metal rings which are in continous contact iwth the brushes. Because they have no gaps, they won't strike on the brushes and thus wear them away, thus making it more reliable and less costly maintenance. This also creates no possibility of electrical short circuit as there are no gaps to strike against. Therefore they are more reliable and have less costly maintenance Funciton of the rotor and the stator Industirally the current is drawn from the stator and the change in magnetic flux is from the rotor. The extra coils are usually added to the stator. This makes the generator still maintain efficiency because there is no extra load added to the rotor. It is also easier to draw a current from a fixed connection to the stator rather than the rotor. Ability to be used with a transformer * Can be used with transformers as it produces a changing magnetic flux, resulting in: * More efficient and cheaper transmission as power loss is reduced (Ploss = I^2R) * More aesthetically pleasing for society because fewer wires are used * More applications with electrical devices requiring different voltages can be used Disadvantage: output - usually consists of 6 stator magnets in pairs around a single electromagnetic rotor with a 3 phase output - a steady voltage cannot be created without a circuit rectifier e.g. a diode bridge to convert from AC to DC - also the voltage from the AC is more dangerous than from DC DC Advantage - usually consists of stator magnets and a rotor with multiple coils placed at regular angels to produce a steady voltage Disadvantage Structure: the bruhses wear away quickly due to the gaps in the 2 semi circular metal rings of the split ring commutator or multi part commutator. This means less efficiency and reliable, and thus it must have costly maintenance. Conductive objects may get lodged in the gaps which may cause electircal sparks and reducing output of the generator Function of the rotor and the stator If more coils re needed, they cannot be on the stator and must go on teh rotor unlike DC. This is becasue in order for the split ring commutator to flip the direction of the current, ithe current must be produced in the rotor. A large current in the commutator-brush connection can lead to electric arcs which can cause explosions around flammable objects. This limtis to relatively lwo voltage application Efficiency and use wtih transformers *D C generators cannot be used with transformers as no changing magnetic flux resulting in: * Higher power loss during transmission which is more expensive * Less aesthetically pleasing for society as more wires required * Electrical devices requiring diffrent voltages require different transmission lines

Gather, analyse and use available evidence to discuss how difficulties of heating caused by eddy currents in transformers may be overcome

Transformers are not 100 percent efficent as energy is lost (usually heat) through Eddy curernts, magnetic hystersis and flux leakage EDDY CURRENTS - the changing magnetic flux in the transformer can through the soft iron core and induce eddy currents which leads to resistve heating loss - the heat can cause damage to the primary and secondary wires, which leads to more resistance and therefore more power loss as P=I^2R. How to minimise 1. Laminating the iron core - the iron core is laminated with thin layers of insulative material with their direction parallel to te magnetic field. This decreases teh SA in which the eddy current can form, therefore leading to less resistive heating loss 2. using a soft ferrite core - it is consisted of complex oxides of iron - they are good ocnductors of flux but bad conductors of electricity. Therefore they have high resistance but low current and therefore lowering the power loss Other methods 1. Cooling fins/heat sinks - they are located on the case of the transformer - they serve to increase the SA which can therefore allow for better dissapation of heat 2. using dark material -- can radiate internal heat rapidly 3. Well ventilated cases -- the air circulation can allow for dissapation of heat 4. Cooling oils -- absorb and dissapate the heat. They circulate from the hotter areas to the cooler areas via convection or circulation assisted by a pump. The case may have design features e.g. cooling tubes and radiator slats to dissapate the heat 5. located away from sunlight and above the ground, open and well ventilated area -- prevents the heat from the external environemtne.g. heat conduction from the ground or radiation from sunlight MAGNETIC HYSTERESIS - energy losses from trying to change the direction of the permanent magnetic field - can be be prevented by using a soft ferromagnetic iron core which has no mangetism when the magnetic field is removed FLUX LEAKAGE - occurs when not all the fliux from the primary coil threads to the secondary coil - prevented by overlapping the priamry coils with the secondary coils

Dicuss the advantages and disadvantages of AC and DC generators and relate these to their use

The advantages and disadvnatges of the AC and DC generator in terms of their strcuture, ablity to be used with transformers and funciton and output are related to their uses STRUCTURE -- AC generator -- > has slip ring commutators which have a smooth, continuous surface in contact with the brushes > there is little wearing away between the brushes and commutators therefore less costly maintenance and replacement -- DC generator -- > has split ring commutator or multi part commutator with gaps that are in contact with the brushes > the brushes will strike against the gaps and therefore wear away the commutator, which will mean more costly maintanence and replacement will be needed, because this wearing away makes the generator less efficient > conductive objects may get lodged between the gaps and therefore cause sparing and reduce the output of the generator ABILITY TO BE USED WITH TRANSFORMER -- AC generator -- > the AC generator produces a changing magnetic flux therefore it can be used with a transformer > this provides many benefits, as it means it is more efficient and cheaper transmission because the transformer can step up or step down the voltage to minimise the power loss as Ploss = I^2 * R > it is also more aestheticlaly pleasing for soceity because less wires are needed for different voltages > more applications with electrical devices requiring different voltages can be used -- DC generator -- > doesn't produce a changing magnetic flux therefore it cannot be used with a transformer > this means it is less aesthetically pleasing for soceity because more wires are requried for different voltages > more expensive and less efficient because there is more poewr loss (Ploss = I^2 * R) > more wires needed for different voltages as they need different trnasmisison lines for differnt electircal devices FUNCITON OF THE ROTOR AND STATOR -- AC generator -- > in the AC generator, it is usually used for high current applications e.g. power stations, thus the current is usually produced in the stator windings rather than the rotor, which creates the magnetic field > by having the addition of the coils on the stator, it reudces the load on the rotor and therefore makes it mroe efficient > it is easier to draw current from a fixed connection on the stator than from the rotor > AC generators which produce the current form the stator do not require slip ring commutators -- DC generator -- > has the current produced in the coils of the rotor rather than the stator in order for the split ring commutator to rotate and reverse the direciton of the current every half turn > this increases teh load on the rotor which makes it less efficient because there is more friction and weaering > drawing high currents from the commutator-brush connection increases the risk of forming electrical arcs, which decreases the fficiency and crates 'radio noise' in the output signal > therefore this meanst he DC genertaor is limited for applicaitons requriing low current OUTPUT SIGNAL -- AC generator -- > AC generators can be designed using 6 stator poles in pairs and a single electromagnetic rotor to produce a 3 phase output signal > this means that AC generators are usually only used for large scale, industrial applications e.g. power stations > the AC generators cannot produce a steady voltage without a circuit rectifier e.g. a diode bridge to conert AC to DC > AC genertaors output more dnagerous than DC which masn increased risk of electrocution -- DC generator -- > designed with multiple rotor coils placed at regular angles to produce a steady voltage > this means it is compatiple with applications requiring steady voltage

State Lenz's Law

The induced EMF or current in a closed loop will be in a direction which opposes the original change in magnetic flux through a coil

What is magnetic field strength and formula

The magnetic flux density B = φ/A

How can the braking effect be reduced

Through using slitted plates, it reduces te size of the eddy currents produced from the change in magneitc flux The adjacent loops are also in opposite directions so some loops will cancel outer = less braking effect due to smaller eddy curens

What is torque and its unit

Torque is the turning momemnt of the force applied perpendicularly to the axis of rotation Measured in Nm τ = Fd or Fcosθd

Explain the role of transformers in electricity substations

Transformers are used to step up or to step down down the voltage to reduce poewr loss, safety and so that they can be used for a variety of appliancse POWER LOSS - at the poewr stations, the transformers ar used to step up the voltage in order to step down the current and tehrefore reduce power loss as Ploss = I^2R - this makes AC electiricty more accessible, more efficient and therefore more cost effective. It also increases transmission distance - electrical resistance in the wries also causes an issue as P = I^2R SAFETY - along the transmisison lines near populated suburban areas, the transformer steps down the voltage for safety because high votlages can increase the chance of electrocution - this is also a lower cost as it reqrueis less insulation APPLIANCES - most appliancse at the home do not need the 240V supplied to the homes - hence transformers are used to step down the voltages for appliacnes such as lighting, phone, laptops etc for safe and efficient operation - this allows for one voltage to be supplied instead of a network of cables to support the votlage requirements

DECRIBE ELECTROMAGNETIC BRAKING SYSTEM + ADV AND DIS

Uses the opposing force produced by the Eddy current to slow down the train HOW IT WORKS > a series of electromagnets with alternating poles are susended above the rails > they are alternating so the eddy currents dont cancel out > As the train movese the raisl epxiernce a change in magntetic flux which induce eddy currents that produce a magnetic field which is in a direction taht opposes the original change in flux > the interaction btween the opposing magnetic field produces an opposing braking force taht slows downt he train, where the force is directly proportional to the speed of the train produced > the trains kinetic energy is converted to electrical energy in the Eddy current via electromagnetic braking which is lost through resistive heating and magnetic hysteresis ADVANTGES > low maintaence becasue there is no physical contact between the rails and brakes thus no wear and tear > smoothign breaking because the braking force is directly proprotional the pseed of the train, thus the brakign effect is reduced as the train slows = smooth stop DISADVANTEGSE > weak braking force -- it is not as strong as the conventional brake pads = cant have a rapid stop > railing heating -- the rails need to be able to withstand high temps from resitive heating

What are the features of a loudspeaker

VOICE COILS > The AC current is passed through the coils from external circuit to induce MF = interacts with ext MF from the cricular permamnent magnets and thus produces a force onto the paper cones i.e. the motor effect, with the direction from RH palm rule CIRCULAR PERMANENT MAGNET > consist of an outer circular ring pole and centrl produce which produce a radial external MF around the coil PAPER CONE > attached to the coil which moves in and out due to the motor effect, causing surrounding air particles to vibrate and produce sound energy AC SIGNAL > frequency and amplitude of the AC signal supplied to the coils determines and pitch and loudness of the sound produced HOW IT WORK An AC signal is passed through the voice coils --> induce MF which interacs with ext MF from circular magnets and thus produces a force due to the motor effect on the paper cone attached to coil Its direction of mvt given by RH palm rule, pushing it in and out This will vibrate the surrounding air particles which will thus produce sound energy Pitch and volume of the sound is affected by the frequency and amplitude of the AC signal supplied

What happens to the motor when: * the motor has no load * the motor has a lod * the motor is stationary or the load is too big What is used to prevent the current surges

WHEN IT HAS NO LOAD * the speed will increase until the supply EMF is almost equal the back EMF WHEN IT HAS A LOAD * usually a motor is operated with a load, which means it will slow it down as the load opposes the motion of coil i.e. the speed will never reach maximum * therefore the back EMF is alwasy less tahn the supply EMF * the larger the load the more it is slowed down WHEN THE MOTOR IS STATION * when the motor is stationary, there is a large current surge from the supply EMF, and there is no back EMF yet because it hasn't turned * to preven the large current surges, variable resistors are placed to prevent burn out. This maximum current will only flow fo ra hsort while * if the load is too big it stops the rotation of the coil and the back EMF will drop to zero, leading to a large current surge from the supply EMF. If the motor exceeds its load, the supply current will continue to flow indefinitely and cause the motoro to burn out

Explain the produciton of eddy currents in terms of lenz's law with the copper plate. How can these effects be minimised?

When a copper plate siwngs like a pendulum in an external magnetic field, it experiences a braking force from the production of the eddy currents. Relates to the motor effect, Faraday;s law and Lenz's law When the copper plate enters the magnetic field, it will create a change in flux due to the relative motin between the plate and the magnetic field. This will induce an eddy current due to Faraday's law, in a direction so that it opposes the original change in flux from Lenz's law. This will create a magnetic field that interacts with the external magnetic field to produce an opposing force onto the plate due to the motor effect, making it experince a braking force that opposes its motion/slows it down i.e. a repulsive force As it exits the magnetic field, this will create a change in flux an thus induce an eddy curernt will be induce in the copper plate due to Faradya's law. It will be in a direction which opposes teh oroginal chagne in flux by Lenz's law. It will produce a amgnetic field which interacts with the external magnetic field so taht the force it produce on the plate is attractive from the motor effect. To minimise: slits can be cut on the plate so that the size of the eddy current is reduced and therefore reducing hte braking effect

What happens when a current carrying loop is placed in a ex MF

When a current carrying loop is placed in an external magnetic field, it will experience a force due to the motor effect, creating a torque on the loop that makes it rotate

What happens when a load is palced on the motor

When a load is placed on the motor, it slows the rotation down, which menas less back EMF Thus there will be more net EMF and current f flowing through the coils to exert torque to the load If too much load is placed, then there will be excess current and EMF flowing through the coil which would cause burn out on the motor

Describe what happens when a magnet moves into a through a conducting loop

When a magnet moves in through a conducting loop, it increaes the magnetic flux thorugh the loop This change in magnetic flux through an increased magnetic field density induces an EMF or current through the conducting loop due to Faraday's law The current will be in a direction that opposes the original change in manetic flux due to Lenz's law Thus a magnetic field that points upwards is required to fulfil this law and oppose the original change in magnetic flux --> creates an EMF that is clockwise direction

Describe the forces when the rectangular current carrying loop is placed in an external magnetic field

When it is placed in an external magnetic field, the MF from the loop will interact with it and produce a force on 2 sides due to the motor effect and create a net torque on the loop The net torque will cause it to rotate clockwise or anti clockwise given by t=nBIAcosθ When the plane of the loop is perpendicular to the MF, the net torque will be 0 but angular momentum allows it to continue to rotate beyond the vertical position When the plane of the loop is beyond the vertical position, the torque will reverse and roster it back to vertical position perpendicular to MF

Describe the net torque on a current carrying loop

When the plane of the coil is parallel to the B field, it will produce a magnetic field which will interact with the external magnetic field and thus produce a force on the 2 sides taht are perpendicular to the B field as F=BILsinθ The net force will produce a torque on the loop as t=nBIAcosθ. This torque will make the coil turn As the plane ofthe coil is at 90 degrees, there is a force but it is unable to make it turn, and the torque is 0 as it is 90 degrees. Angular momentum will allow for it to continue trotating beyond the vertical position However once ti si on the other side, the current is 'reversed' thus making it turn the opposite direction from the torque back into the orignal position. Thus it will rock back and forth from anti to clockwise. Maximum torque when 180s

Explain back EMF in electrical motors (using formula as well)

iThe relative motion between the rotation of the coils and the external magnetic field induces an EMF and current through the coils due to Faradays law The direction fo the back EMF will be so that it opposes the original change in magnetic flux aka back emf (Lenz's law) The back EMF opposes the supply EMF from the external circuit. The εnet (voltage) that rotates across the coil is given by: εnet = εsupply - εback = IR 1. The coil in originally station where εnet = εsupply 2. As the current is supplied from the external circuit, it begins to rotate 3. As it begins to rotate, the relative motion between the rotating coils and the external magnetic field causes a change in magnetic flux and induce back EMF. It will be in a direction such that it opposes the original change in magnetic flux due to Lenz's law, and thus oppose the net current 4. As it begins to rotate faster (due to torque, as torque is just acceleration) = greater change in magnetic flux (the rate of change of magneitc flux is directly proportional to the amount of induced EMF) = more back EMF opposing the supply EMF 5. Thus the net EMF begins to decrease as the back EMF continues to increase until it is almost equal to the supply EMF (it will never equal the supply EMF as there will be alwasy frictional forces). This small amount of net EMF is required to overcome the frictional forces and continue rotating. Thus is will be rotating at a maximum constant speed when this occurs

Why does torque vary on a DC motor

varies because when it rotates to diffeernet positions, there is a different angle to the MF, which therefore affects the toqrque > the variation in torque thus varies teh speed in the motor however DC motors need constant rotational speed