Current Electricity 1

7/30/2019 Current Electricity 1

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Current Electricity 1

Copyright M air e Duffy, Clonkeen College

For non-commercial purposes only Enjoy!

Please leave feedback on the Physics H omepage Forum


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Electricity> Did you know?7 percent of power generated at large central

stations is lost during transmission to the userover high-voltage lines!1 lightening bolt has enough power to service200 000 homes!!An electric eel can produce a voltage of up to

650 Volts!!20 mA of current running through your bodycan stop your heart!!


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Potential Difference (V)Potential difference is the work done per unit charge to transfer acharge from one point to another(also Voltage)

i.e V = WQ

Unit Volt V or J C-1 Volt is the p.d. between two pointsif one joule of work is done bringing

one coulomb from one point to theotherPotential at a point is the p.d.between a point and the Earth,where the Earth is at zero potential


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Capacitance (C)Capacitance is the ratio of the charge on a conductor

to its p.d.i.e. C = Q V

Unit Farad F or C V -1

Parallel Plate CapacitorC = A

d A = area of overlap of platesd = distance between plates

= permittivity of dielectric (insulator between plates)

Capacitor stores charge


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CapacitorsCapacitor uses

Allow a.c. to flow but block d.c.Tune in radio stations(variable capacitor)

Smooth out variations ind.c.Camera flashFiltering: allow certainfrequencies of analternating signal to passbut block others
http://images.google.ie/imgres?imgurl=http://www.mainlinegroup.co.uk/jacksonbrothers/5250big.jpg&imgrefurl=http://www.mainlinegroup.co.uk/jacksonbrothers/5250.htm&h=595&w=664&sz=43&tbnid=HrhLTqBcRJOyOM:&tbnh=121&tbnw=136&hl=en&start=84&prev=/images%3Fq%3Dcapacitors%26start%3D80%26svnum%3D10%26hl%3Den%26lr%3D%26sa%3DN


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Energy Stored in a Charged Capacitor To charge a capacitor one plate is

connected to + terminal and the otherto terminal and the power supply isturned on

An equal charge builds up on oneplate and a + charge on the otherThis charge remains even whendisconnected from the power supplyIt can be discharged by connecting it

to a conductorW = CV 2

http://lectureonline.cl.msu.edu/~mmp/kap23/RC/app.htm
http://lectureonline.cl.msu.edu/~mmp/kap23/RC/app.htmhttp://lectureonline.cl.msu.edu/~mmp/kap23/RC/app.htmhttp://lectureonline.cl.msu.edu/~mmp/kap23/RC/app.htmhttp://lectureonline.cl.msu.edu/~mmp/kap23/RC/app.htm


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Electric Current (I)This is the flow of electriccharge{In a metal conductor it isthe flow of electrons}Size of current in a conductoris the amount of chargepassing any point of thatconductor per secondQ = It

Unit Amp A or C s -1


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Electric Current SummaryElectrons flow from to +

+ _

e-

e-

d.c. direct current flows in one direction in aclosed circuit, it is caused by a power supplya.c. alternating current is when the currentconstantly reverses direction e.g. mains currentalternates 100 times per second

Conventional current flows from + to i.e. flow of positive charge


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Current is the same at every point in a series closed circuit cct

Sum of current flowing into a junction equals sum of currentflowing out of junction

Ammeter is used to measure current and is always connectedin series in the cct

Electric Current Summary

Galvanometer is a sensitive ammeter/microammeter


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Potential Difference (V)This can also be said to be the energy lost by 1coulomb as it moves between 2 points in a circuit

i.e. V = W

Q

Note: W = VQ Divide both sides by t (time)W = VQ

t t P = VI (P = W and I = Q ) t t


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Voltage (V) Voltages in seriesV = V 1 + V 2 + V 3

Voltages in parallelV 1 = V 2 = V 3

Voltmeter is used to measure voltage and is alwaysconnected in parallel with the part of the cct to bemeasured


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Voltages in Series and Parallel


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Electromotive Force (e.m.f.)e.m.f. (E) is a voltage

applied to a cct.Unit Volt

http://video.google.com/videoplay?docid=-6226504780579469841

Electric cell is a device thatconverts chemical energy into

electrical energy and is asource of e.m.f.Sources

Simple CellPrimary CellSecondary CellThermocoupleMains
http://video.google.com/videoplay?docid=-6226504780579469841http://video.google.com/videoplay?docid=-6226504780579469841http://video.google.com/videoplay?docid=-6226504780579469841http://video.google.com/videoplay?docid=-6226504780579469841


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Simple Cell Copper and zinc plates areelectrodesDilute sulphuric acid andcopper sulphate is theelectrolyte

Plates chemically react with theacid leaving the plates chargedCopper electrode is a positiveCathodeZinc electrode is a negativeanodeThis simple cell cant berecharged as the chemicals areused up as a current flows

e.m.f. generated is 1V

Zn

-Cu

+

Anode Cathode

e-e-

Cu

Zn 2+

Zn

Cu 2+


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Primary Cell

This type of cell cant be recharged. Also known as dry cells as the electrolyte tends tobe a chemical paste.


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Secondary Cell

This is a cell that can be recharged Also known as an accumulatore.g. car battery is a lead-acid accumulator


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CreditsSlide 2: Lightning Bolt Image

http://www.msha.gov/Accident_Prevention/Tips/lightning.htm Electric eel image ~ Amy Lebeau

www.nfpa.org/riskwatch/teach_eslp_pkk_04.html

Slide 3: Animation ~ Irina Nelson and Johnny Ericksonwww.slcc.edu/schools/hum_sci/physics/tutor/2220/e_potential

Slide 4: NoneSlide 5: First capacitor image

www.mainlinegroup.co.uk/jacksonbrothers/5250.htm Slide 6: Capacitor image ~ Christopher Borg

http://qarnita.tripod.com/comp.htm Slide 7: Bulb and battery animation ~ David Chase Edventures.com

http://discover.edventures.com/functions/termlib.php?action=&termid=153&alpha=c&searchstring =

Electric Motor animation ~ UK Motion Gallerywww.bbc.co.uk/science/robots/techlab/v_rollerbots.shtml

Slide 8: None Slide 9: None Slide 10: None Slide 11: Voltages in series image ~ Andrew Turner Primary School Science

www.primaryschoolscience.com/about/about_assessment.php Slide 12: Voltages in series and parallel image ~ Graham Knot

http://ourworld.compuserve.com/homepages/g_knott/elect27.htm

Slide 13: Lemon battery image and video link ~ Carol and Wayne Campbellwww.hilaroad.com/camp/projects/lemon/lemon_battery.html Note : google video player needs to be downloaded from the web page to play video clip

Slide 14: None Slide 15: Battery image ~ EDF Energy

www.edfenergy.com/powerup/keystage3/in/page2.html Slide 16: Lead-acid battery image ~ EUROBAT The Association of European Storage Battery Manufacturers.

www.mpoweruk.com/cell_construction.htm
http://www.msha.gov/Accident_Prevention/Tips/lightning.htmhttp://www.nfpa.org/riskwatch/teach_eslp_pkk_04.htmlhttp://www.slcc.edu/schools/hum_sci/physics/tutor/2220/e_potentialhttp://www.mainlinegroup.co.uk/jacksonbrothers/5250.htmhttp://qarnita.tripod.com/comp.htmhttp://discover.edventures.com/functions/termlib.php?action=&termid=153&alpha=c&searchstringhttp://www.bbc.co.uk/science/robots/techlab/v_rollerbots.shtmlhttp://www.primaryschoolscience.com/about/about_assessment.phphttp://ourworld.compuserve.com/homepages/g_knott/elect27.htmhttp://www.hilaroad.com/camp/projects/lemon/lemon_battery.htmlhttp://www.edfenergy.com/powerup/keystage3/in/page2.htmlhttp://www.mpoweruk.com/cell_construction.htmhttp://www.mpoweruk.com/cell_construction.htmhttp://www.edfenergy.com/powerup/keystage3/in/page2.htmlhttp://www.hilaroad.com/camp/projects/lemon/lemon_battery.htmlhttp://ourworld.compuserve.com/homepages/g_knott/elect27.htmhttp://www.primaryschoolscience.com/about/about_assessment.phphttp://www.bbc.co.uk/science/robots/techlab/v_rollerbots.shtmlhttp://discover.edventures.com/functions/termlib.php?action=&termid=153&alpha=c&searchstringhttp://qarnita.tripod.com/comp.htmhttp://www.mainlinegroup.co.uk/jacksonbrothers/5250.htmhttp://www.slcc.edu/schools/hum_sci/physics/tutor/2220/e_potentialhttp://www.nfpa.org/riskwatch/teach_eslp_pkk_04.htmlhttp://www.msha.gov/Accident_Prevention/Tips/lightning.htm

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Current Electricity 1