current electricity 1 copyright © maire duffy, clonkeen college for non-commercial purposes only...
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Current Current Electricity 1Electricity 1
Copyright © Maire Duffy, Clonkeen College
For non-commercial purposes only Enjoy!
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ElectricityElectricity> Did you know?> Did you know?
7 percent of power generated at large central stations is lost during transmission to the user over high-voltage lines!
1 lightening bolt has enough power to service 200 000 homes!! An electric eel can produce a voltage of up to 650 Volts!! 20 mA of current running through your body can stop your heart!!
Potential Difference (V)Potential Difference (V) Potential difference is the
work done per unit charge to transfer a charge from one point to another (also Voltage)
i.e V = W Q
Unit Volt V or J C-1
Volt is the p.d. between two points if one joule of work is done bringing one coulomb from one point to the other
Potential at a point is the p.d. between a point and the Earth, where the Earth is at zero potential
Capacitance (C)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 Capacitor C = A
dA = area of overlap of platesd = distance between plates = permittivity of dielectric (insulator between
plates)
Capacitor stores charge
CapacitorsCapacitorsCapacitor uses
Allow a.c. to flow but block d.c.
Tune in radio stations (variable capacitor)
Smooth out variations in d.c.
Camera flash Filtering: allow certain
frequencies of an alternating signal to pass but block others
EnergyEnergy Stored in a Charged Stored in a Charged CapacitorCapacitor
To charge a capacitor one plate is connected to + terminal and the other to – terminal and the power supply is turned on
An equal – charge builds up on one plate and a + charge on the other
This charge remains even when disconnected from the power supply
It can be discharged by connecting it to a conductor
W = ½ CV 2
http://lectureonline.cl.msu.edu/~mmp/kap23/RC/app.htm
Electric Current Electric Current (I)(I)
This is the flow of electric charge
{In a metal conductor it is the flow of electrons}
Size of current in a conductor is the amount of charge passing any point of that conductor per second
Q = It Unit Amp A or C s-1
Electric Current Electric Current SummarySummary
Electrons flow from – to +
+_
e-
e-
d.c. direct current flows in one direction in a closed circuit, it is caused by a power supplya.c. alternating current is when the current constantly reverses direction e.g. mains current alternates 100 times per second
Conventional current flows from + to – i.e. flow of positive charge
Current is the same at every point in a series closed circuit cct
Sum of current flowing into a junction equals sum of current flowing out of junction
Ammeter is used to measure current and is always connected in series in the cct
Electric Current SummaryElectric Current Summary
Galvanometer is a sensitive ammeter/microammeter
Potential Difference Potential Difference (V)(V)
This can also be said to be the energy lost by 1 coulomb as it moves between 2 points in a circuit
i.e. V = W Q
Note:Note: W = VQ Divide both sides by t (time)
W = VQ t tP = VI (P = W and I = Q )
t t
Voltage (V)Voltage (V) Voltages in seriesV = V1 + V2 + V3
Voltages in parallel V1 = V2 = V3
Voltmeter is used to measure voltage and is always connected in parallel with the part of the cct to be measured
Electromotive ForceElectromotive Force (e.m.f.)(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 that converts chemical energy into electrical energy and is a source of e.m.f.Sources
Simple CellPrimary CellSecondary CellThermocoupleMains
Simple CellSimple Cell Copper and zinc plates are
electrodes Dilute sulphuric acid and copper
sulphate is the electrolyte Plates chemically react with the
acid leaving the plates charged Copper electrode is a positive
Cathode Zinc electrode is a negative
anode This simple cell can’t be
recharged as the chemicals are used up as a current flows
e.m.f. generated is 1V
Zn
-
Cu
+
Anode Cathode
e-e-
Cu
Zn2+
Zn
Cu2+
Primary CellPrimary Cell
This type of cell can’t be recharged. Also known as dry cells as the electrolyte
tends to be a chemical paste.
Secondary CellSecondary Cell
This is a cell that can be recharged Also known as an accumulator e.g. car battery is a lead-acid
accumulator
CreditsCredits Slide 2: Slide 2: Lightning Bolt Image
http://www.msha.gov/Accident_Prevention/Tips/lightning.htmElectric eel image ~ Amy Lebeau
www.nfpa.org/riskwatch/teach_eslp_pkk_04.html Slide 3:Slide 3: Animation ~ Irina Nelson and Johnny Erickson
www.slcc.edu/schools/hum_sci/physics/tutor/2220/e_potential Slide 4:Slide 4: None Slide 5:Slide 5: First capacitor image
www.mainlinegroup.co.uk/jacksonbrothers/5250.htm Slide 6:Slide 6: Capacitor image ~ Christopher Borg
http://qarnita.tripod.com/comp.htm Slide 7: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 Gallery
www.bbc.co.uk/science/robots/techlab/v_rollerbots.shtml Slide 8:Slide 8: None Slide Slide 9: 9: None Slide 10:Slide 10:None Slide 11:Slide 11: Voltages in series image ~ Andrew Turner Primary School Science
www.primaryschoolscience.com/about/about_assessment.php Slide 12:Slide 12: Voltages in series and parallel image ~ Graham Knot
http://ourworld.compuserve.com/homepages/g_knott/elect27.htm Slide 13:Slide 13: Lemon battery image and video link ~ Carol and Wayne Campbell
www.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:Slide 14: None Slide 15:Slide 15: Battery image ~ EDF Energy
www.edfenergy.com/powerup/keystage3/in/page2.html Slide 16:Slide 16: Lead-acid battery image ~ EUROBAT The Association of European Storage Battery Manufacturers.
www.mpoweruk.com/cell_construction.htm