Understanding Electricity Understanding Electricity
Common units Back to basics Electrical energy The labels on electrical devices usually show one or more of the following The area of a rectangle is found by multiplying the length What flows in an electric circuit is electric charge. The amount of energy symbols: W, V, A and maybe Hz. But what do they mean and what by the width. The reason why is not hard to see. that the charge carries is specified by the electric potential (potential information do they provide? Manufacturers use these symbols to inform It takes a little more effort to see why multiplying the difference or voltage). One volt means ‘one joule per coulomb’. In summary, users so that they can operate appliances safely. In this lesson we will voltage by the electric current gives the power. the current (in amperes) is the rate of flow of charge (in coulombs per explore the meaning of the symbols and the quantities they represent 3 × 4 = 12 second); the voltage (in volts) specifies the amount of energy carried by and show how to interpret them correctly. Electric charge and electric current each coulomb. EirGrid is responsible for a safe, secure and reliable supply Symbol Unit Meaning Watts, volts and amperes If you rub a balloon on your clothes it may become of electricity: Now and in the future. electrically charged and be able to attract small C coulomb the unit of electric charge The labels on typical domestic appliances show values such as the following: bits of paper or hair. Similar effects occur when We develop, manage and operate the electricity transmission the unit of electric current, the rate of flow of amber is rubbed with cloth or fur – an effect A ampere grid. This brings power from where it is generated to where Hair drier 230 V, 750 W electric charge in coulombs per second. that has been a source of curiosity for thousands it is needed – throughout Ireland. We use our grid to supply Bulb 230 V, 40 W of years. The unit of electric charge is called a the unit of electric potential. The voltage tells you power to industry and businesses that use large amounts Phone charger 100 – 240 V, 200 mA, 50 – 60 Hz coulomb, named after Charles de Coulomb who, how much energy each coulomb carries. of electricity. Our grid also powers the distribution network. in the 1780s, investigated the forces of attraction V volt In Europe the voltage is 230 V; in the USA it This supplies the electricity you use everyday in your homes, Jug kettle 230 V, 2300 W and repulsion between charges. mains is 120 V. businesses, schools, hospitals, and farms. The plugs on domestic appliances are commonly marked ‘13 A’. This The diagram shows two oppositely charged conducting lesson will explain what these units mean and how they are related. the unit of power, the rate at which energy is spheres on insulating stands. As long as there is no W watt We develop new electricity infrastructure only when required. transferred, in joules per second How are the units related? conductor linking them the charges will not move. EirGrid is a state-owned company, but we answer to However, if a conductor links them then the charge the unit of frequency. In Europe the mains government and to regulators. We work for the benefit and Volts, amperes (colloquially known as ‘amps’) and watts are related as follows: can move. Hz hertz frequency is 50 Hz (or 50 cycles per second); safety of every citizen in Ireland; we abide by strict laws watts = volts × amperes The movement or flow of electric charge is called an in the USA the mains frequency is 60 Hz. and safety standards. Let’s take the example of the jug kettle listed above; the label shows ‘230 electric current. If the charge flows atone coulomb Consider a simple circuit with a 6 volt battery and a bulb marked 6 V, 2 A. V, 2300 W’. We can use these values to find the electric current per second, we say the electric current is one ampere. How much energy is lost by the bulb every second as light and heat? (in amperes). (1 A = 1 C / s ) The current is 2 amperes, i.e. two coulombs watts = volts × amperes In a similar way the rate of flow of water from a tap per second. Every second two coulombs leave 2300 = (230) (x) could be expressed in litres per second. the battery, two coulombs enter the bulb, two coulombs leave the bulb and two coulombs By re-arranging we can find x. Extending the water analogy return to the battery. The rate of flow of charge x = 2300 / 230 is the same throughout the circuit. Consider a heating system with a = 10 amperes boiler and radiator. Water is heated The battery is marked ‘6 V’. This means that This indicates that the electric current in the jug kettle is 10 amperes and pumped around the system. Radiator every coulomb leaving the battery brings 6 joules of energy with it. (10 A). So why is the plug on the kettle marked ‘13 A’? The rate of flow of water is the same 60 °C So, since 2 coulombs leave every second and each brings 6 joules of in all parts of the system. In this case → energy, the rate at which energy leaves the battery is: 55 °C Safety, fuses and 13 A water is used to move heat (energy) Boiler = 6 × 2 J/s from the boiler to the radiator. & pump = 12 J/s (or 12 watts) Electric current produces a heating effect and excessive currents can cause insulation on wires to melt. In Ireland and many other European The amount of heat that is delivered countries the maximum current that should be drawn from mains to the room by the radiator depends Origin of electrical units electrical sockets is 13 amperes. In order to prevent damage a fuse on: Prior to the SI system of units (1960) we had the MKS (metre -kilogram- is fitted in the plugs of all standard electrical appliances. The current • the rate of flow of water second, from 1901) and CGS (centimetre-gram-second from 1832) systems. In 1874 James Clerk Maxwell extended the CGS system rating of the fuse should exceed the anticipated maximum current for • the temperature drop. the appliance but must not exceed 13 amperes. If for any reason the to include electrical units. At the First International Conference of current rises above 13 A, then a thin wire in the fuse melts and cuts off In the case of water, a temperature difference of 1 °C is equivalent to an Electricians (Paris,1881) the following units were adopted: the ohm, volt, the electric current to the appliance. energy difference of over 4000 joules per litre of water (4181 J, to be ampere, coulomb and farad. The discovery of the electron in 1897 precise). Suppose the water flows at 0.1 litres per second and drops from did not change these units. Refinements of the definitions of some units What are watts? 60 °C to 55 °C at what rate is heat transferred to the room? In this case have been made on occasion but, in practice, they have not noticeably the heat energy transferred every second is approximately: changed. Since 1881 the unit of electric charge is the coulomb (symbol Domestic light bulbs are manufactured in a variety of specifications. = (0.1) × (4000) × (60 − 55) C) and the unit of electric current is the ampere (symbol A). One ampere A bulb marked ‘80 W’ would be expected to be brighter than a bulb of the (1 A) is equal to one coulomb per second (1 C/s). same kind that is marked ‘40 W’. The letter ‘W’ stands for ‘watt’ and the = (0.1) × (20,000) You can find out more about the work of EirGrid at value indicates how much energy the bulb radiates every second. = 2000 J/s Note: In metals the charge carriers are electrons. The charge on an electron www.eirgrid.com –19 The watt is the unit of power; one watt means one joule per second. = 2000 W is 1.602 × 10 C. In aqueous solutions the charge carriers are generally Lamps of different types, but with the same power, may have different positive and negative ions. In a solution of copper sulfate, with copper In this system the water is merely the carrier of energy; it goes into the , the charge is carried entirely by positive copper ions (Cu++). light outputs. For example, a 40 W fluorescent lamp generally gives out electrodes radiator and comes out again having left some energy behind. In a similar In gases the charge carriers are usually both positive and negative ions as more light than a 40 W incandescent bulb. In other words, some devices Find this and other lessons on www.sta.ie way electric charge comes into our houses on one wire and returns on well as electrons. So, electric current is sometimes a flow of electrons are more efficient than others. another but it leaves energy behind. and sometimes it is not. However, it is always a flow of electric charge. Understanding Electricity Understanding Electricity
Common units Back to basics Electrical energy The labels on electrical devices usually show one or more of the following The area of a rectangle is found by multiplying the length What flows in an electric circuit is electric charge. The amount of energy symbols: W, V, A and maybe Hz. But what do they mean and what by the width. The reason why is not hard to see. that the charge carries is specified by the electric potential (potential information do they provide? Manufacturers use these symbols to inform It takes a little more effort to see why multiplying the difference or voltage). One volt means ‘one joule per coulomb’. In summary, users so that they can operate appliances safely. In this lesson we will voltage by the electric current gives the power. the current (in amperes) is the rate of flow of charge (in coulombs per explore the meaning of the symbols and the quantities they represent 3 × 4 = 12 second); the voltage (in volts) specifies the amount of energy carried by and show how to interpret them correctly. Electric charge and electric current each coulomb. EirGrid is responsible for a safe, secure and reliable supply Symbol Unit Meaning Watts, volts and amperes If you rub a balloon on your clothes it may become of electricity: Now and in the future. electrically charged and be able to attract small C coulomb the unit of electric charge The labels on typical domestic appliances show values such as the following: bits of paper or hair. Similar effects occur when We develop, manage and operate the electricity transmission the unit of electric current, the rate of flow of amber is rubbed with cloth or fur – an effect A ampere grid. This brings power from where it is generated to where Hair drier 230 V, 750 W electric charge in coulombs per second. that has been a source of curiosity for thousands it is needed – throughout Ireland. We use our grid to supply Bulb 230 V, 40 W of years. The unit of electric charge is called a the unit of electric potential. The voltage tells you power to industry and businesses that use large amounts Phone charger 100 – 240 V, 200 mA, 50 – 60 Hz coulomb, named after Charles de Coulomb who, how much energy each coulomb carries. of electricity. Our grid also powers the distribution network. in the 1780s, investigated the forces of attraction V volt In Europe the voltage is 230 V; in the USA it This supplies the electricity you use everyday in your homes, Jug kettle 230 V, 2300 W and repulsion between charges. mains is 120 V. businesses, schools, hospitals, and farms. The plugs on domestic appliances are commonly marked ‘13 A’. This The diagram shows two oppositely charged conducting lesson will explain what these units mean and how they are related. the unit of power, the rate at which energy is spheres on insulating stands. As long as there is no W watt We develop new electricity infrastructure only when required. transferred, in joules per second How are the units related? conductor linking them the charges will not move. EirGrid is a state-owned company, but we answer to However, if a conductor links them then the charge the unit of frequency. In Europe the mains government and to regulators. We work for the benefit and Volts, amperes (colloquially known as ‘amps’) and watts are related as follows: can move. Hz hertz frequency is 50 Hz (or 50 cycles per second); safety of every citizen in Ireland; we abide by strict laws watts = volts × amperes The movement or flow of electric charge is called an in the USA the mains frequency is 60 Hz. and safety standards. Let’s take the example of the jug kettle listed above; the label shows ‘230 electric current. If the charge flows atone coulomb Consider a simple circuit with a 6 volt battery and a bulb marked 6 V, 2 A. V, 2300 W’. We can use these values to find the electric current per second, we say the electric current is one ampere. How much energy is lost by the bulb every second as light and heat? (in amperes). (1 A = 1 C / s ) The current is 2 amperes, i.e. two coulombs watts = volts × amperes In a similar way the rate of flow of water from a tap per second. Every second two coulombs leave 2300 = (230) (x) could be expressed in litres per second. the battery, two coulombs enter the bulb, two coulombs leave the bulb and two coulombs By re-arranging we can find x. Extending the water analogy return to the battery. The rate of flow of charge x = 2300 / 230 is the same throughout the circuit. Consider a heating system with a = 10 amperes boiler and radiator. Water is heated The battery is marked ‘6 V’. This means that This indicates that the electric current in the jug kettle is 10 amperes and pumped around the system. Radiator every coulomb leaving the battery brings 6 joules of energy with it. (10 A). So why is the plug on the kettle marked ‘13 A’? The rate of flow of water is the same 60 °C So, since 2 coulombs leave every second and each brings 6 joules of in all parts of the system. In this case → energy, the rate at which energy leaves the battery is: 55 °C Safety, fuses and 13 A water is used to move heat (energy) Boiler = 6 × 2 J/s from the boiler to the radiator. & pump = 12 J/s (or 12 watts) Electric current produces a heating effect and excessive currents can cause insulation on wires to melt. In Ireland and many other European The amount of heat that is delivered countries the maximum current that should be drawn from mains to the room by the radiator depends Origin of electrical units electrical sockets is 13 amperes. In order to prevent damage a fuse on: Prior to the SI system of units (1960) we had the MKS (metre -kilogram- is fitted in the plugs of all standard electrical appliances. The current • the rate of flow of water second, from 1901) and CGS (centimetre-gram-second from 1832) systems. In 1874 James Clerk Maxwell extended the CGS system rating of the fuse should exceed the anticipated maximum current for • the temperature drop. the appliance but must not exceed 13 amperes. If for any reason the to include electrical units. At the First International Conference of current rises above 13 A, then a thin wire in the fuse melts and cuts off In the case of water, a temperature difference of 1 °C is equivalent to an Electricians (Paris,1881) the following units were adopted: the ohm, volt, the electric current to the appliance. energy difference of over 4000 joules per litre of water (4181 J, to be ampere, coulomb and farad. The discovery of the electron in 1897 precise). Suppose the water flows at 0.1 litres per second and drops from did not change these units. Refinements of the definitions of some units What are watts? 60 °C to 55 °C at what rate is heat transferred to the room? In this case have been made on occasion but, in practice, they have not noticeably the heat energy transferred every second is approximately: changed. Since 1881 the unit of electric charge is the coulomb (symbol Domestic light bulbs are manufactured in a variety of specifications. = (0.1) × (4000) × (60 − 55) C) and the unit of electric current is the ampere (symbol A). One ampere A bulb marked ‘80 W’ would be expected to be brighter than a bulb of the (1 A) is equal to one coulomb per second (1 C/s). same kind that is marked ‘40 W’. The letter ‘W’ stands for ‘watt’ and the = (0.1) × (20,000) You can find out more about the work of EirGrid at value indicates how much energy the bulb radiates every second. = 2000 J/s Note: In metals the charge carriers are electrons. The charge on an electron www.eirgrid.com –19 The watt is the unit of power; one watt means one joule per second. = 2000 W is 1.602 × 10 C. In aqueous solutions the charge carriers are generally Lamps of different types, but with the same power, may have different positive and negative ions. In a solution of copper sulfate, with copper In this system the water is merely the carrier of energy; it goes into the , the charge is carried entirely by positive copper ions (Cu++). light outputs. For example, a 40 W fluorescent lamp generally gives out electrodes radiator and comes out again having left some energy behind. In a similar In gases the charge carriers are usually both positive and negative ions as more light than a 40 W incandescent bulb. In other words, some devices Find this and other lessons on www.sta.ie way electric charge comes into our houses on one wire and returns on well as electrons. So, electric current is sometimes a flow of electrons are more efficient than others. another but it leaves energy behind. and sometimes it is not. However, it is always a flow of electric charge. UnderstandingUnderstanding Electricity Electricity Understanding Electricity
SyllabusSyllabus References References StudentStudent Activities Activities ExaminationExamination Questions Questions DidDid You You Know? Know? TheThe main main syllabus syllabus references references for for the the lesson lesson are: are: 1.1. Most Most electrical electrical units units are are named named after after people people • • TheThe East–West East–West Interconnector Interconnector is isa high-voltagea high-voltage direct direct current current whowho made made important important discoveries discoveries relating relating to to electricity: electricity: coulomb, coulomb, LeavingLeaving Certificate Certificate Physics Physics (OL) (OL) 2003 2003 Q. Q.8 8 cablecable between between Ireland Ireland and and Wales. Wales. It operatesIt operates at at400 400 kV kV LeavingLeaving Certificate Certificate Physics Physics 8. 8. WhatWhat is isan an electric electric current? current? (6)(6) E E NN volt,volt, ampere, ampere, watt, watt, joule, joule, ohm. ohm. a)a) What What is isan an electric electric current? current? (i.e.(i.e. –200 –200 kV kV to to+ +200 200 kV) kV) and and has has a powera power rating rating of of500 500 MW MW • • PotentialPotential difference: difference: Definition Definition of ofpotential potential difference: difference: work work done done per per (500(500 million million watts). watts). DeviseDevise a aposter, poster, or or a acomputer computer presentation, presentation, on on one one of of these these b)b) Give Give the the standard standard colour colour of of the the insulation insulation unitunit charge charge to totransfer transfer a chargea charge from from one one point point to toanother. another. (p. (p. 34) 34) units.units. Include Include a ashort short biography biography of of the the person person in inwhose whose honour honour GiveGive the the onstandard on standardthe the wires colourwires colour connected ofconnected ofthe the insulation insulation to to each eachon on theof theof thewires thewires L L • • The The interconnector interconnector uses uses direct direct current current in incontrast contrast to tothe the national national • • ElectricElectric current: current: Description Description of of electric electric current current as as flow flow of ofcha charge;rge; thethe unit unit is isnamed, named, an an explanation explanation of of the the unit unit and and what what it it connectedconnectedterminals toterminals toeach each of ofL,the L,the Nterminals Nandterminals and E L,Eon L,onN the Nand the and plugE plugonE on thein the in theplug theplug gridgrid which which uses uses alternating alternating current current (AC). (AC). There There is isless less energy energy loss loss in in –1 –1 transmissiontransmission using using DC DC (direct (direct current) current) but but conversion conversion from from AC AC to toDC DC 1 A1 A= =1 1C Cs s (p. (p. 35) 35) measuresmeasures and and how how the the unit unit relates relates to to some some other other units. units. Include Include in inthe the diagram. diagram.diagram.diagram. What What What is What isth eth ispurposee ispurposethe the purpose of purpose ofthe the wire wire of connected of theconnected the wire wire relevantrelevant graphics. graphics. is isrequired required at atthe the source source and and from from DC DC back back to toAC AC at atthe the receiving receiving • • Sources Sources of of emf emf and and electric electric current. current. Potential Potential difference difference (pd) (pd) and and to tothe the terminal terminalconnectedconnected E onE on the theto plug? to theplug? the terminal terminal E Eon on the the plug? plug?(15)(15) end.end. DC DC transmission transmission is isfeasible feasible only only for for relatively relatively long long distances distances voltagevoltage are are the the same same thing; thing; they they are are measured measured in involts. volts. (p. (p. 35) 35) 2.2. Make Make a aposter poster or or a acomputer computer presentation presentation on on fuses fuses and and MCBs MCBs c)c) Explain Explain why why a afuse fuse is isused used in ina aplug. plug. becausebecause of ofthe the extra extra expense expense involved. involved. (or(or similar similar safety safety devices). devices). Outline Outline how how the the devices devices work work and and ExplainExplain why why a fusea fuse is isused used in ina plug.a plug. (6)(6) • • DomesticDomestic circuits: circuits: Plugs, Plugs, fuses, fuses, MCBs MCBs ...... safety safety precautions. precautions. (p. (p. 37) 37) • • It links It links the the British British and and Irish Irish electricity electricity markets. markets. The The cable cable is is261 261 whywhy they they are are important. important. Include Include relevant relevant graphics. graphics. d)d) The The fuse fuse in inthe the plug plug of of an an electric electric kettle kettle TheThe fuse fuse wasin wasinthe the replacedplug replacedplug of ofan an electricwith electricwith a kettlea5 kettleA5 Afuse. was fuse. was replaced Thereplaced The kettle withkettle with a 5a A5 Afuse. fuse. The The kettle kettle has has a powera power kilometreskilometres long, long, 186 186 of ofwhich which are are under under the the sea. sea. It runsIt runs between between LeavingLeaving Certificate Certificate Technology Technology WoodlandWoodland in inMeath Meath and and Deeside Deeside in inWales. Wales. 3.3. Make Make a alist list of of ten ten electrically electrically powered powered devices devices in inthe the lab lab or or in in ratingrating of ofhas2 kWhas2 kW a when a powerwhen power connected connected rating rating to of tothe of 2the ESB2kW ESB kW mainswhen mainswhen voltage connectedvoltage connected of of230 230 V.to V.to the the electric electric mains mains • • Electricity Electricity as as a forma form of ofenergy energy distribution. distribution. Basic Basic electrical electrical concepts: concepts: youryour home. home. Examine Examine the the labels labels on on them them to to find find what what their their power power voltagevoltage of of 230 230 V. V. Calculate Calculate the the current current that that flows flows when when the the kettle kettle • • Construction Construction began began in in2007 2007 and and was was completed completed in in2012. 2012. electricelectric current, current, voltage, voltage, resistance, resistance, power power and and the the relationship relationship CalculateCalculate the the current current that that flows flows when when the the kettle kettle is isfirst first plugged plugged in. in. is isand and note note it init ina atable. table. For For each each device device estimate estimate the the length length of of is isfirst first plugged plugged in. in. This This current current will will only only flow flow for for a avery very short short time. time. TheThe project project won won the the Best Best Engineering Engineering Project Project 2014 2014 at atboth both the the betweenbetween them. them. 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(9)(9) TransitionTransition Year Year classes. classes. thethe voltage voltage that that is isused used to to power power it byit by the the current current that that flows flows throughthrough it. it.Make Make a aposter poster a acomputer computer presentation presentation to to explain explain f) f) Name Name a adevice device that that is isoften often used used nowadays nowadays in indomestic domestic electric electric BiographicalBiographical Notes Notes NameName a devicea device that that is isoften often used used nowadays nowadays in indomestic domestic electric electric circuits circuits instead instead of offuses. fuses. (5) (5) whywhy ‘power ‘power = =current current × ×voltage’. voltage’. circuitscircuits instead instead of of fuses. fuses. CharlesCharles Coulomb Coulomb (1736 (1736 – –1806) 1806) (P ( P= =VI VI) ) LearningLearning Outcomes Outcomes 5.5. UseUse the the Internet, Internet, or or other other sources sources of of information, information, to to find find what what (P(P = =VI) VI) stepssteps can can be be taken taken to to make make more more efficient efficient use use of ofenergy energy or or Charles-AugustinCharles-Augustin Coulomb Coulomb was was born born into into LeavingLeaving Certificate Certificate Physics Physics (HL) (HL) 2010 2010 Q. Q.8 8 th th reducereduce energy energy loss loss in inthe the home home or or in inschool. school. Examples Examples include: include:8. 8. A Ahair hair dryer dryer with with a plastica plastic casing casing uses uses a coileda coiled wire wire as asa heata heat source. source. anan aristocratic aristocratic family family on on 14 14 June June 1736 1736 in in OnOn completion completion of of this this lesson, lesson, students students should should be be able able to: to: A Ahair hair dryer dryer with with a aplastic plastic casing casing uses uses a acoiled coiled wire wire as as a aheat heat source. source. solarsolar heating heating panels, panels, photovoltaic photovoltaic panels, panels, wind wind power power and and WhenWhen an anelectric electric current current flows flows through through the the coiled coiled wire, wire, the the air air around around Angoulême,Angoulême, France, France, and and while while he he was was still still it heatsit heats up up andWhen andWhen a motorised a motorised an an electric electricfan fan blows blows current thecurrent the hot hot airflows air flowsout. out. through through the the coiled coiled wire, wire, the the air air around around • • Explain Explain what what is ismeant meant by by electric electric current current and and electrical electrical potential potential improvedimproved insulation. insulation. Summarise Summarise you you findings findings in in a aposter poster of of 9. 9. WhatWhat is isa magnetica magnetic field? field? (6)(6) a achild child the the family family moved moved to to Paris. Paris. In In school school it heatsit heats up up and and a amotorised motorised fan fan blows blows the the hot hot air air out. out. • • Explain Explain what what is ismeant meant by by ‘power’ ‘power’ (rate (rate of of use use of of energy) energy) computercomputer presentation. presentation. WhatWhat is anis anelectric electric current? current? hehe developed developed a aflair flair for for mathematicsmathematics and and at at TheThe earth earth has has a magnetica magnetic field. field. Give Give one one use use of ofthe the earth’s earth’s magnetic magnetic field. field. (5)(5) collegecollege he he studied studied engineering. engineering. • • Calculate Calculate power power in ina acircuit circuit given given the the current current and and voltage voltage 6.6. FindFind out out why why the the electricity electricity transmission transmission grid grid operates operates at at voltages voltages Heating Heating is oneisWhat oneWhat effect effect is of isan ofan an anelectric electric current. current.current? current? Heating Heating is isone one effect effect of of an an electric electric GiveGive twoHans two Hansother current.other current.Oersted effectsOersted effects ofGive discovered ofGiveandiscovered anelectric two electric two other current. theother current.the magneticeffects magneticeffects ofeffect of aneffect an electric of electric(12) of(12)an an electriccurrent. electriccurrent. current current in in1820 1820 while while • • Explain Explain why why the the product product of of current current and and voltage voltage gives gives the the power power ofof over over 110,000 110,000 volts: volts: 110 110 kV, kV, 220 220 kV, kV, 275 275 kV kV or or 400 400 kV. kV. 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T T F F rheostatrheostat is isadjusted adjusted (aIn)( a Inan) Whatan experiment, What experiment, is theis the initial initiala thina resistance thin resistance lig light htconductor of conductor ofthe the coil? coil? is isplaced placed between betweenfusefuse HeHe studied studied the the forces forces involved involved in intwisting twisting wires wires and and published published a a GeneralGeneral Learning Learning Points Points b)b) Electric Electric potential potential is ismeasured measured in injoules. joules. T T F F (bthe)( bthe )poles Calculate poles Calculate •of • of whena the U-shaped whena theU-shaped current currentswitch switch magnetthat magnetthat Aflows Aflowsand as and throughasshown switch throughshown switch inthe in the Bcoil the B coilarediagram. arediagram. paperpaper on on the the subject subject in in1784. 1784. He He devised devised a asensitive sensitive balance balance for for DescribeDescribewhenwhen whatthe whatclosed.the dryerclosed. happensdryer happens is turnedis turnedwhen when on. on. a current a current flows flows through through(9) the(9) the measuringmeasuring these these torsional torsional forces. forces. With With this, this, he he measured measured the the forces forces c)c) One One ampere ampere means means ‘one ‘one coulomb coulomb per per second’. second’. T T F F conductor.conductor. TheseThese are are additional additional relevant relevant points points which which are are (iii)(iii) A Alength length(ii)(ii) of The ofnichrome The nichrome maximum maximum wire wire of ofdiameter power diameter power 0.17 generated 0.17 generated mm mm is usedis used in in NSNS ofof attraction attraction and and repulsion repulsion between between electric electric charges charges and and discovered discovered d)d) The The power power of of an an electric electric appliance appliance is ismeasured measured in inwatts. watts. NameName two two devices devices that that are are based based on on the the effect effect 230230 V V MM coilcoil usedused to to extend extend knowledge knowledge and and facilitate facilitate discussion. discussion. forfor the the coil. coil.the Calculatethe Calculateheating heating the the lengcoil lengcoilth is thof is 2ofthe 2kW.the coilkW. coil of ofwire. wire. (18) (18) demonstrateddemonstrated in inthis this experiment. experiment. (12)(12) fanfan thatthat they they follow follow and and inverse-square inverse-square law. law. In In recognition recognition of of this this work work OneOne watt watt means means one one joule joule per per minute. minute. T T F F(iv)(iv) Explain Explain why why the the current current through through the the coil coil would would decrease decrease • • What What is isthe the initial initial resistance resistance of of thethe unit unit of of electric electric charge charge (the (the coulomb) coulomb) is isnamed named after after him. him. • • ElectricElectric charge charge is ismeasured measured in incoulombs coulombs (symbol: (symbol: C). C). This This unit unit was was e)e) The The power power of of an an electric electric appliance appliance can can be be found found by by if theif the fan fan developed developed a fault a fault and and stopped stopped working. working. (8) (8) –19–19 WhatWhat would would happen happen if if(i) (i) a laa rgerlarger current current flowed flowed in inthe the (A(A flow flow rate rate of ofone one coulomb coulomb per per second second is iscalled called an an ampere.) ampere.) agreedagreed in in1881. 1881. The The charge charge on on an an electron electron is is1.602 1.602 × ×10 10 C. C. thethe coil? coil? –6 –6 conductorconductor multiplyingmultiplying the the electric electric current current by by the the voltage. voltage. T T F F (resistivityconductor,(resistivityconductor, of (ii) ofnichrome (ii) nichrome the the current current= 1.1= 1.1 fl× owed 10fl× owed10 Ω in Ωm inthe m) the )opposite opposite direction direction • •Calculate Calculate the the current current that that flows flows CoulombCoulomb died died in in1806 1806 after after a aten-year ten-year illness. illness. • • ElectricElectric current current is isa aflow flow of ofelectric electric charge. charge. The The rate rate of offlow flow of of f) f) The The maximum maximum current current that that should should be be drawn drawn from from a a throughthrough the the conductor? conductor? (6)(6) throughthrough the the coil coil when when the the dryer dryer is isturned turned on. on. chargecharge is isexpressed expressed in inamperes, amperes, i.e. i.e. coulombs coulombs per per second. second. domesticdomestic mains mains electric electric outlet outlet is is13 13 amperes. amperes. T T F F 9. 9. WhatWhat is thermionicis thermionic(iii)(iii) A Alengthemission? lengthemission? of of nichrome nichrome wire wire of of diameter diameter 0.17 0.17 mm mm is isused used (6)for (6)for the the • • TheThe energy energy ‘carried’ ‘carried’ by by each each coulomb coulomb is isspecified specified by bythe the voltage. voltage. g)g) In InIreland Ireland the the voltage voltage used used for for domestic domestic mains mains is is120 120 V. V. T T F F OneOne volt volt means means ‘one ‘one joule joule per per coulomb’. coulomb’. coil.coil. Calculate Calculate the the length lengthPage Pageof of 6the of 6the 12of coil12 coil of of wire. wire. h)h) Electric Electric potential potential is isalso also known known as as ‘voltage’. ‘voltage’. T T F FX-raysX-rays are are produced produced when when high-energy high-energy electrons electrons collide collide with with a target. a target. ReviseRevise The The Terms Terms • • The The product product of of the the current current and and the the voltage voltage gives gives the the power, power, (iv)(iv) Explain Explain why why the the current current through through the the coil coil would would decrease decrease if theif the fan fan i.e.i.e. the the rate rate of of use use or or transfer transfer of of energy. energy. i) i) The The heat heat transferred transferred to to a aroom room by by a aradiator radiator depends depends DrawDraw a labelled a labelled diagramdeveloped diagramdeveloped of ofan anX-ray a X-ray afault faulttube. tube. and and stopped stopped working. working. (12)(12) CanCan you you recall recall the the meaning meaning of ofthe the following following terms? terms? onon the the rate rate of of flow flow of ofwater water and and the the temperature temperature WhatWhat are are X-rays X-rays and and how (resistivity how (resistivity do do they they differ ofdiffer of nichromefrom nichromefrom light light rays? =rays? =1.1 1.1 × ×10 10–6 –6Ω Ωm m ) ) RevisingRevising terminology terminology is isa powerfula powerful aid aid to torecall recall and and retention. retention. • • The The use use of of water water in ina aheating heating system system is isanalogous analogous the the use use differencedifference between between the the inlet inlet and and outlet outlet pipes. pipes. T T F F ofof electricity electricity to to transfer transfer energy. energy. The The rate rate of of flow flow of ofwater water is is GiveGive two two uses uses of ofX-rays. X-rays. (18)(18) amber,amber, ampere, ampere, coulomb, coulomb, electric electric current, current, electric electric potential, potential, electric electric analogousanalogous to to the the rate rate of of flow flow of ofelectric electric charge. charge. The The heat heat energy energy j) j) The The heat heat transferred transferred to to a aroom room by by an an electric electric heater heater LeavingLeaving Certificate Certificate Technology Technology (HL) (HL) 2010 2010 Q. Q.2 (c)2 (c) charge,charge, electrode, electrode, electron, electron, energy, energy, farad, farad, fluorescent, fluorescent, frequency, frequency, transferredtransferred by by the the water water is isanalogous analogous to to the the voltage voltage in inan an electric electric dependsdepends on on the the rate rate of of flow flow of ofcharge charge and and the the potential potential WhenWhen electrons electronsA ADC hitDC hit motorthe motorthe target target consumes consumesin inan anX-ra X-ray 2tube,y 2wattstube, watts only only of a of smallpowera smallpower percentage percentageand and delivers deliversof oftheir their 1.6 1.6 watts watts of of incandescent,incandescent, insulation, insulation, ion, ion, joule, joule, ohm, ohm, power, power, quantity, quantity, SI SI units, units, differencedifference between between the the inlet inlet and and outlet outlet conductors. conductors. T T F Fenergyenergy is convertedis converted into into X-rays. X-rays. What What happens happens to tothe the rest rest of oftheir their energy energy and and how how symbol,symbol, volt, volt, voltage, voltage, watt. watt. circuit.circuit. The The voltage voltage specifies specifies how how muchmuch energy energy (in (in joules) joules) that that doesdoes this this influence powerinfluencepower the at the typeat the type the of output oftarget output target used? shaft.used? shaft. Calculate Calculate the the efficiency efficiency of ofthe the motor(9)motor(9) and and eacheach coulomb coulomb caries. caries. explainexplain why why this this efficiency efficiency is isnot not 100%. 100%. CheckCheck your your answers answers to to these these questions questions on on www.sta.ie www.sta.ie A potentialA potential difference difference (voltage) (voltage) of of40 40 kV kV is appliedis applied across across an anX-ray X-ray tube. tube. CheckCheck the the Glossary Glossary of of terms terms for for this this lesson lesson on on www.sta.ie www.sta.ie • • watts watts = =amperes amperes × ×volts volts Calculate:Calculate: (i) (i) the the maximum maximum energy energy of ofan anelectron electron as asit hitsit hits the the target target (ii)(ii) the the frequency frequency of ofthe the most most energetic energetic X-ray X-ray produced. produced. (11)(11)
(Plank(Plank constant constant = 6.6= 6.6 × 10× 10–34–34 J s J ; scharge ; charge on on electron electron = 1.6= 1.6 × 10× 10–19–19 C) C)
pagepage 7 of 7 12of 12
UnderstandingUnderstanding Electricity Electricity Understanding Electricity
SyllabusSyllabus References References StudentStudent Activities Activities ExaminationExamination Questions Questions DidDid You You Know? Know? TheThe main main syllabus syllabus references references for for the the lesson lesson are: are: 1.1. Most Most electrical electrical units units are are named named after after people people • • TheThe East–West East–West Interconnector Interconnector is isa ahigh-voltage high-voltage direct direct current current whowho made made important important discoveries discoveries relating relating to to electricity: electricity: coulomb, coulomb, LeavingLeaving Certificate Certificate Physics Physics (OL) (OL) 2003 2003 Q. Q.8 8 cablecable between between Ireland Ireland and and Wales. Wales. It Itoperates operates at at 400 400 kV kV LeavingLeaving Certificate Certificate Physics Physics 8. 8. WhatWhat is isan an electric electric current? current? (6)(6) E E NN volt,volt, ampere, ampere, watt, watt, joule, joule, ohm. ohm. a)a) What What is isan an electric electric current? current? (i.e.(i.e. –200 –200 kV kV to to + +200 200 kV) kV) and and has has a apower power rating rating of of 500 500 MW MW • • PotentialPotential difference: difference: Definition Definition of ofpotential potential difference: difference: work work done done per per (500(500 million million watts). watts). DeviseDevise a aposter, poster, or or a acomputer computer presentation, presentation, on on one one of of these these b)b) Give Give the the standard standard colour colour of of the the insulation insulation unitunit charge charge to to transfer transfer a acharge charge from from one one point point to to another. another. (p. (p. 34) 34) units.units. Include Include a ashort short biography biography of of the the person person in in whose whose honour honour GiveGive the the onstandard on standardthe the wires colourwires colour connected ofconnected ofthe the insulation insulation to to each eachon on theof theof thewires thewires L L • • The The interconnector interconnector uses uses direct direct current current in incontrast contrast to to the the national national • • ElectricElectric current: current: Description Description of of electric electric current current as as flow flow of ofcha charge;rge; thethe unit unit is isnamed, named, an an explanation explanation of of the the unit unit and and what what it it connectedconnectedterminals toterminals toeach each of ofL,the L,the Nterminals Nterminalsand and E EL,on L,onN the Nand the and plugE plugEon on thein thein theplug theplug gridgrid which which uses uses alternating alternating current current (AC). (AC). There There is isless less energy energy loss loss in in –1 –1 transmissiontransmission using using DC DC (direct (direct current) current) but but conversion conversion from from AC AC to to DC DC 1 1A A= =1 1C Cs s (p. (p. 35) 35) measuresmeasures and and how how the the unit unit relates relates to to some some other other units. units. Include Include in inthe the diagram. diagram.diagram.diagram. What What What isWhat isth eth ispurposee ispurposethe the purpose of purpose ofthe the wire wire of connectedof theconnected the wire wire relevantrelevant graphics. graphics. is isrequired required at at the the source source and and from from DC DC back back to to AC AC at at the the receiving receiving • • Sources Sources of of emf emf and and electric electric current. current. Potential Potential difference difference (pd) (pd) and and to tothe the terminal terminalconnectedconnected E onE on the theto plug? to plug?the the terminal terminal E Eon on the the plug? plug?(15)(15) end.end. DC DC transmission transmission is isfeasible feasible only only for for relatively relatively long long distances distances voltagevoltage are are the the same same thing; thing; they they are are measured measured in in volts. volts. (p. (p. 35) 35) 2.2. Make Make a aposter poster or or a acomputer computer presentation presentation on on fuses fuses and and MCBs MCBs c)c) Explain Explain why why a afuse fuse is isused used in in a aplug. plug. becausebecause of of the the extra extra expense expense involved. involved. (or(or similar similar safety safety devices). devices). Outline Outline how how the the devices devices work work and and ExplainExplain why why a fusea fuse is isused used in ina plug.a plug. (6)(6) • • DomesticDomestic circuits: circuits: Plugs, Plugs, fuses, fuses, MCBs MCBs ...... safety safety precautions. precautions. (p. (p. 37) 37) • • It Itlinks links the the British British and and Irish Irish electricity electricity markets. markets. The The cable cable is is261 261 whywhy they they are are important. important. Include Include relevant relevant graphics. graphics. d)d) The The fuse fuse in in the the plug plug of of an an electric electric kettle kettle TheThe fuse fuse wasin wasinthe the replacedplug replacedplug of ofan an electricwith electricwith a kettlea5 kettle5A Afuse. was fuse. was replaced Thereplaced The kettle withkettle with a 5a A5 Afuse. fuse. The The kettle kettle has has a powera power kilometreskilometres long, long, 186 186 of of which which are are under under the the sea. sea. It Itruns runs between between LeavingLeaving Certificate Certificate Technology Technology WoodlandWoodland in inMeath Meath and and Deeside Deeside in inWales. Wales. 3.3. Make Make a alist list of of ten ten electrically electrically powered powered devices devices in in the the lab lab or or in in ratingrating of ofhas2 kWhas2 kW a when a powerwhen power connected connected rating rating to of tothe of 2the ESB2kW ESB kW mainswhen mainswhen voltage connectedvoltage connected of of230 230 V.to V.to the the electric electric mains mains • • Electricity Electricity as as a aform form of of energy energy distribution. distribution. Basic Basic electrical electrical concepts: concepts: youryour home. home. Examine Examine the the labels labels on on them them to to find find what what their their power power voltagevoltage of of 230 230 V. V. Calculate Calculate the the current current that that flows flows when when the the kettle kettle • • Construction Construction began began in in2007 2007 and and was was completed completed in in2012. 2012. electricelectric current, current, voltage, voltage, resistance, resistance, power power and and the the relationship relationship CalculateCalculate the the current current that that flows flows when when the the kettle kettle is isfirst first plugged plugged in. in. is isand and note note it itin in a atable. table. For For each each device device estimate estimate the the length length of of is isfirst first plugged plugged in. in. This This current current will will only only flow flow for for a avery very short short time. time. TheThe project project won won the the Best Best Engineering Engineering Project Project 2014 2014 at at both both the the betweenbetween them. them. The The units units in inwhich which electric electric current, current, voltage, voltage, ThisThis current current will will only only flow flow for for a vea very ryshort short time. time. Explain Explain why. why. (15)(15) timetime it itis isused used in in a ayear year and and calculate calculate the the total total energy energy use use in in ExplainExplain why. why. EngineersEngineers Ireland Ireland Excellence Excellence Awards Awards and and the the Irish Irish Building Building resistance,resistance, power power and and frequency frequency are are measured measured (p. (p. 22) 22) kilowatt-hours.kilowatt-hours. andand Design Design Awards. Awards. e)e) Bonding Bonding is isa asafety safety precaution precaution used used in in domestic domestic electric electric circuits. circuits. ScienceScience and and Technology Technology in in Action Action is isalso also widely widely used used by by 4.4. The The power power of of an an electrical electrical device device can can be be found found by by multiplying multiplying BondingBonding is isa safetya safety precaution precaution used used in indomestic domestic electric electric circuits. circuits. How How does does bonding bonding improve improve safetysafety in inHowthe Howthe home? home?does does bonding bonding improve improve safety safety in in the the home? home? (9)(9) TransitionTransition Year Year classes. classes. thethe voltage voltage that that is isused used to to power power it itby by the the current current that that flows flows throughthrough it. it. Make Make a aposter poster a acomputer computer presentation presentation to to explain explain f) f) Name Name a adevice device that that is isoften often used used nowadays nowadays in in domestic domestic electric electric BiographicalBiographical Notes Notes NameName a devicea device that that is isoften often used used nowadays nowadays in indomestic domestic electric electric circuits circuits instead instead of offuses. fuses. (5) (5) whywhy ‘power ‘power = =current current × ×voltage’. voltage’. circuitscircuits instead instead of of fuses. fuses. CharlesCharles Coulomb Coulomb (1736 (1736 – –1806) 1806) (P ( P= =VI VI) ) LearningLearning Outcomes Outcomes 5.5. UseUse the the Internet, Internet, or or other other sources sources of of information, information, to to find find what what (P(P = =VI) VI) stepssteps can can be be taken taken to to make make more more efficient efficient use use of ofenergy energy or or Charles-AugustinCharles-Augustin Coulomb Coulomb was was born born into into LeavingLeaving Certificate Certificate Physics Physics (HL) (HL) 2010 2010 Q. Q.8 8 th th reducereduce energy energy loss loss in in the the home home or or in in school. school. Examples Examples include: include:8. 8. A Ahair hair dryer dryer with with a plastica plastic casing casing uses uses a coileda coiled wire wire as asa heata heat source. source. anan aristocratic aristocratic family family on on 14 14 June June 1736 1736 in in OnOn completion completion of of this this lesson, lesson, students students should should be be able able to: to: A Ahair hair dryer dryer with with a aplastic plastic casing casing uses uses a acoiled coiled wire wire as as a aheat heat source. source. solarsolar heating heating panels, panels, photovoltaic photovoltaic panels, panels, wind wind power power and and WhenWhen an an electric electric current current flows flows through through the the coiled coiled wire, wire, the the air air around around Angoulême,Angoulême, France, France, and and while while he he was was still still it heatsit heats up up andWhen andWhen a motoriseda motorised an an electric electricfan fan blows blows current currentthe the hot hot airflows air flowsout. out. through through the the coiled coiled wire, wire, the the air air around around • • Explain Explain what what is ismeant meant by by electric electric current current and and electrical electrical potential potential improvedimproved insulation. insulation. Summarise Summarise you you findings findings in in a aposter poster of of 9. 9. WhatWhat is isa magnetica magnetic field? field? (6)(6) a achild child the the family family moved moved to to Paris. Paris. In In school school it itheats heats up up and and a amotorised motorised fan fan blows blows the the hot hot air air out. out. • • Explain Explain what what is ismeant meant by by ‘power’ ‘power’ (rate (rate of of use use of of energy) energy) computercomputer presentation. presentation. WhatWhat is anis an electric electric current? current? hehe developed developed a aflair flair for for mathematicsmathematics and and at at TheThe earth earth has has a magnetica magnetic field. field. Give Give one one use use of ofthe the earth’s earth’s magnetic magnetic field. field. (5)(5) collegecollege he he studied studied engineering. engineering. • • Calculate Calculate power power in in a acircuit circuit given given the the current current and and voltage voltage 6.6. FindFind out out why why the the electricity electricity transmission transmission grid grid operates operates at at voltages voltages Heating Heating is oneisWhat oneWhat effect effect is of isan ofan an anelectric electric current. current.current? current? Heating Heating is isone one effect effect of of an an electric electric GiveGive twoHans two Hansother current.other current.Oersted effectsOersted effects ofGive discovered ofGiveandiscovered an electric two electric two other current. theother current.the magneticeffects magneticeffects ofeffect of aneffect an electric of electric(12) of(12)an an electriccurrent. electriccurrent. current current in in1820 1820 while while • • Explain Explain why why the the product product of of current current and and voltage voltage gives gives the the power power ofof over over 110,000 110,000 volts: volts: 110 110 kV, kV, 220 220 kV, kV, 275 275 kV kV or or 400 400 kV. kV. FromFrom 1861 1861 he he worked worked for for about about twelve twelve years years demonstratingdemonstrating electricity electricity to tohis his students. students. Describe Describe how how you you would would demonstrate demonstrate the the magnetic magnetic TheThe diagram diagramThe showsThe shows diagram adiagram basica basic electrical showselectrical shows circuit acircuit abasic basicfor for a hairelectricala hairelectrical dryer. dryer. onon structural structural engineering engineering projects projects in in different different • • ShowShow how how the the flow flow of ofwater water in in a aheating heating system system is is analogous analogous to to effecteffect of ofan an electric electric current. current. (18)(18) countries,countries, including including the the West West Indies. Indies. In In 1773, 1773, (i)(i) DescribeDescribecircuitcircuit what what forhappens: forhappens: a ahair hair dryer. dryer. thethe flow flow of ofcharge charge in in an an electric electric circuit circuit followingfollowing an an illness, illness, he he returned returned to to France. France. (a)( a) when when switch switch A Ais closedis closed and and the the rheostat rheostat is adjustedis adjusted A A • • Use Use electrical electrical units units correctly. correctly. DrawDraw(i) a(i) sketcha Describe sketch Describe of ofthe the whatmagnetic whatmagnetic happens: happens: field field around around a straa straightight wire wire carrying carrying a current.a current. Your Your diagram diagram HeHe began began to to publish publish academic academic papers papers on on mathematical mathematical and and True/FalseTrue/False Questions Questions (bshould)( bshould) when whenshow show switch switch the the Adirection Adirectionand and switch switch of ofthe B the areB current are currentclosed. closed. and and the the directi directi(9)on(9) on of ofthe the magnetic magnetic field. field. (9)(9) • • when when switch switch A Ais isclosed closed and and the the engineeringengineering problems problems for for which which he he won won awards. awards. (ii)(ii) TheThe maximum maximum power power generated generated in inthe the heating heating coil coil is 2is kW.2 kW. B B a)a) Electric Electric charge charge is ismeasured measured in in coulombs. coulombs. T T F F rheostatrheostat is isadjusted adjusted (aIn)( a Inan) Whatan experiment, What experiment, is theis the initial initiala thina resistance thin resistance lig light htconductor of conductor ofthe the coil? coil? is isplaced placed between betweenfusefuse HeHe studied studied the the forces forces involved involved in in twisting twisting wires wires and and published published a a GeneralGeneral Learning Learning Points Points b)b) Electric Electric potential potential is ismeasured measured in in joules. joules. T T F F (bthe)( bthe )poles Calculate poles Calculate •of • of whena theU-shaped whena theU-shaped current currentswitch switch magnetthat magnetthat Aflows Aflowsand as and asthroughshown switchthroughshown switch inthe inthe the Bcoil the B coilarediagram. arediagram. paperpaper on on the the subject subject in in 1784. 1784. He He devised devised a asensitive sensitive balance balance for for DescribeDescribewhenwhen whatthe whatclosed.the dryerclosed. happensdryer happens is turnedis turnedwhen when on. on. a currenta current flows flows through through(9) the(9) the measuringmeasuring these these torsional torsional forces. forces. With With this, this, he he measured measured the the forces forces c)c) One One ampere ampere means means ‘one ‘one coulomb coulomb per per second’. second’. T T F F conductor.conductor. TheseThese are are additional additional relevant relevant points points which which are are (iii)(iii) A Alength length(ii)(ii) of The ofnichrome The nichrome maximum maximum wire wire of ofdiameter power diameter power 0.17 generated 0.17 generated mm mm is usedis used in in NSNS ofof attraction attraction and and repulsion repulsion between between electric electric charges charges and and discovered discovered d)d) The The power power of of an an electric electric appliance appliance is ismeasured measured in in watts. watts. NameName twotwo devicesdevices thatthat areare basedbased onon thethe effecteffect 230230 V V MM coilcoil usedused to to extend extend knowledge knowledge and and facilitate facilitate discussion. discussion. forfor the the coil. coil.the Calculatethe Calculate heating heating the the lengcoil lengcoilth is thof is 2ofthe 2kW.the coilkW. coil of ofwire. wire. (18) (18) demonstrateddemonstrated in inthis this experiment. experiment. (12)(12) fanfan thatthat they they follow follow and and inverse-square inverse-square law. law. In In recognition recognition of of this this work work OneOne watt watt means means one one joule joule per per minute. minute. T T F F(iv)(iv) Explain Explain why why the the current current through through the the coil coil would would decrease decrease • • What What is isthe the initial initial resistance resistance of of thethe unit unit of of electric electric charge charge (the (the coulomb) coulomb) is isnamed named after after him. him. • • ElectricElectric charge charge is ismeasured measured in incoulombs coulombs (symbol: (symbol: C). C). This This unit unit was was e)e) The The power power of of an an electric electric appliance appliance can can be be found found by by if theif the fan fan developed developed a faulta fault and and stopped stopped working. working. (8) (8) –19–19 WhatWhat would would happen happen if if(i) (i) a laa rgerlarger current current flowed flowed in inthe the (A(A flow flow rate rate of ofone one coulomb coulomb per per second second is is called called an an ampere.) ampere.) agreedagreed in in1881. 1881. The The charge charge on on an an electron electron is is1.602 1.602 × ×10 10 C. C. thethe coil? coil? –6 –6 conductorconductor multiplyingmultiplying the the electric electric current current by by the the voltage. voltage. T T F F (resistivityconductor,(resistivityconductor, of (ii) ofnichrome (ii) nichrome the the current current= 1.1= 1.1 fl× owed 10fl× owed10 Ω in Ωm inthe m) the )opposite opposite direction direction • •Calculate Calculate the the current current that that flows flows CoulombCoulomb died died in in 1806 1806 after after a aten-year ten-year illness. illness. • • ElectricElectric current current is isa aflow flow of ofelectric electric charge. charge. The The rate rate of offlow flow of of f) f) The The maximum maximum current current that that should should be be drawn drawn from from a a throughthrough the the conductor? conductor? (6)(6) throughthrough the the coil coil when when the the dryer dryer is isturned turned on. on. chargecharge is isexpressed expressed in in amperes, amperes, i.e. i.e. coulombs coulombs per per second. second. domesticdomestic mains mains electric electric outlet outlet is is13 13 amperes. amperes. T T F F 9. 9. WhatWhat is thermionicis thermionic(iii)(iii) A Alengthemission? lengthemission? of of nichrome nichrome wire wire of of diameter diameter 0.17 0.17 mm mm is isused used (6)for (6)for the the • • TheThe energy energy ‘carried’ ‘carried’ by by each each coulomb coulomb is isspecified specified by by the the voltage. voltage. g)g) In InIreland Ireland the the voltage voltage used used for for domestic domestic mains mains is is120 120 V. V. T T F F OneOne volt volt means means ‘one ‘one joule joule per per coulomb’. coulomb’. coil.coil. Calculate Calculate the the length lengthPage Pageof of 6the of 6the 12of coil12 coil of of wire. wire. h)h) Electric Electric potential potential is isalso also known known as as ‘voltage’. ‘voltage’. T T F FX-raysX-rays are are produced produced when when high-energy high-energy electrons electrons collide collide with with a target.a target. ReviseRevise The The Terms Terms • • The The product product of of the the current current and and the the voltage voltage gives gives the the power, power, (iv)(iv) Explain Explain why why the the current current through through the the coil coil would would decrease decrease if ifthe the fan fan i.e.i.e. the the rate rate of of use use or or transfer transfer of of energy. energy. i) i) The The heat heat transferred transferred to to a aroom room by by a aradiator radiator depends depends DrawDraw a labelleda labelled diagramdeveloped diagramdeveloped of ofan an X-ray a X-ray afault fault tube. tube. and and stopped stopped working. working. (12)(12) CanCan you you recall recall the the meaning meaning of of the the following following terms? terms? onon the the rate rate of of flow flow of ofwater water and and the the temperature temperature WhatWhat are are X-rays X-rays and and how (resistivity how (resistivity do do they they differ differof of nichromefrom nichromefrom light light rays? rays?= =1.1 1.1 × ×10 10–6 –6Ω Ωm m ) ) RevisingRevising terminology terminology is isa apowerful powerful aid aid to to recall recall and and retention. retention. • • The The use use of of water water in in a aheating heating system system is isanalogous analogous the the use use differencedifference between between the the inlet inlet and and outlet outlet pipes. pipes. T T F F ofof electricity electricity to to transfer transfer energy. energy. The The rate rate of of flow flow of ofwater water is is GiveGive two two uses uses of ofX-rays. X-rays. (18)(18) amber,amber, ampere, ampere, coulomb, coulomb, electric electric current, current, electric electric potential, potential, electric electric analogousanalogous to to the the rate rate of of flow flow of ofelectric electric charge. charge. The The heat heat energy energy j) j) The The heat heat transferred transferred to to a aroom room by by an an electric electric heater heater LeavingLeaving Certificate Certificate Technology Technology (HL) (HL) 2010 2010 Q. Q.2 (c)2 (c) charge,charge, electrode, electrode, electron, electron, energy, energy, farad, farad, fluorescent, fluorescent, frequency, frequency, transferredtransferred by by the the water water is isanalogous analogous to to the the voltage voltage in in an an electric electric dependsdepends on on the the rate rate of of flow flow of ofcharge charge and and the the potential potential WhenWhen electrons electronsA ADC DChit hit motorthe motorthe target target consumes consumesin inan an X-ra X-ray 2tube,y 2wattstube, watts only only of a of smallapower smallpower percentage percentage and and delivers deliversof oftheir their 1.6 1.6 watts watts of of incandescent,incandescent, insulation, insulation, ion, ion, joule, joule, ohm, ohm, power, power, quantity, quantity, SI SI units, units, differencedifference between between the the inlet inlet and and outlet outlet conductors. conductors. T T F Fenergyenergy is convertedis converted into into X-rays. X-rays. What What happens happens to tothe the rest rest of oftheir their energy energy and and how how symbol,symbol, volt, volt, voltage, voltage, watt. watt. circuit.circuit. The The voltage voltage specifies specifies how how muchmuch energy energy (in (in joules) joules) that that doesdoes this this influence powerinfluencepower the at the typeat the type the of output oftarget output target used? shaft.used? shaft. Calculate Calculate the the efficiency efficiency of ofthe the motor(9)motor(9) and and eacheach coulomb coulomb caries. caries. explainexplain why why this this efficiency efficiency is is not not 100%. 100%. CheckCheck your your answers answers to to these these questions questions on on www.sta.ie www.sta.ie A Apotential potential difference difference (voltage) (voltage) of of40 40 kV kV is appliedis applied across across an an X-ray X-ray tube. tube. CheckCheck the the Glossary Glossary of of terms terms for for this this lesson lesson on on www.sta.ie www.sta.ie • • watts watts = =amperes amperes × ×volts volts Calculate:Calculate: (i)(i) the the maximum maximum energy energy of ofan an electron electron as asit hitsit hits the the target target (ii)(ii) the the frequency frequency of ofthe the most most energetic energetic X-ray X-ray produced. produced. (11)(11)
(Plank(Plank constant constant = 6.6= 6.6 × 10× 10–34–34 J s J ; scharge ; charge on on electron electron = 1.6= 1.6 × 10× 10–19–19 C) C)
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