IVE Basic Concepts of electricity

IVE SI Units In science and engineering the International System of Units (SI units) form the basis of all units used.

IVE Six base units in SI system Quantity UnitUnit symbol Electric currentampereAElectric currentampereA MasskilogramkgMasskilogramkg LengthmetremLengthmetrem TimesecondsTimeseconds TemperaturekelvinKTemperaturekelvinK Luminous intensitycandelacdLuminous intensitycandelacd

IVE Basic Electrical Units Quantity UnitUnit symbol Potential volts VPotential volts V PowerWatt WPowerWatt W EnergyJoule/Watt hour J/WhEnergyJoule/Watt hour J/Wh ResistanceOhm ΩResistanceOhm Ω FrequencyHertz HzFrequencyHertz Hz

IVE Common Prefixes Multiplying factor Prefix nameSymbol teraT teraT 10 9 gigaG10 9 gigaG 10 6 megaM10 6 megaM 10 3 kilok10 3 kilok millim10 -3 millim micro μ10 -6 micro μ nanon10 -9 nanon picop picop

IVE Atom model Nucleus Electron

IVE Atom ProtonsProtons NeutronsNeutrons ElectronsElectrons Each atom has the same number of protons and electronsEach atom has the same number of protons and electrons

IVE Proton and Electron Protons carries positive chargeProtons carries positive charge –it is relatively large mass –does not play active part in electrical current flow Electrons carries negative charge Electrons carries negative charge –light mass –play an important role in electrical current flow

IVE Unit of Charge Unit of Charge is called Coulomb (C)Unit of Charge is called Coulomb (C) An electron and a proton have exactly same amount of chargeAn electron and a proton have exactly same amount of charge One coulomb of charge is equal to approximately 628 x electron chargeOne coulomb of charge is equal to approximately 628 x electron charge

IVE Free Electrons Applying Heat or Light

IVE Electrical Materials All material may be classified into three major classesAll material may be classified into three major classes –conductors –insulators –semiconductors

IVE Electrical Materials conductors have many free electrons which will be drifting in a random manner within the material insulators have very few free electrons semiconductors falls somewhere between these two extremes

IVE Electric current Electric current is the movement, or flow of electrons through a conductive material It is measured as the rate at which the charge is moved around a circuit, its unit is ampere (A) I=Q/t or Q=It

IVE Electromotive Force In order to cause the 'free' electrons to drift in a given direction an electromotive force must be applied The emf is the 'driving' force in an electrical circuit The symbol for emf is E and the unit of measurement is the volt (V)

IVE Electromotive Force Typical sources of emf are cells, batteries and generators The amount of current that will flow through a circuit is related to the size of the emf applied to it

IVE Potential Difference (p.d.) Whenever current flows through a circuit element in a circuit such as resistor, there will be a potential difference(p.d.) developed across it The unit of p.d. is volts(V) and is measured as the difference in voltage levels between two points in a circuit

IVE Potential Difference (p.d.) Emf (being the driving force) causes current to flow potential difference is the result of current flowing through a circuit element Thus emf is a cause and p.d. is an effect

IVE Potential Difference (p.d.) LOAD P.D.=1.4 V E.m.f.=1.5V, R int. Equivalent circuit of a battery

IVE Resistance Resistance is the 'opposition' to the current flow measured in ohms ( Ω ) Conductors have a low value of resistance Insulators have a very high resistance

IVE Resistor Substances, which offer certain amount of resistance to the flow of electrons, are called resistors The resistance of a resistor depends on the material used, the physical construction of the resistor and the temperature

IVE Resistor The resistance value can be determined by the equationThe resistance value can be determined by the equation –R is the resistance of a resistor in ohm(  ) –l is the length of the resistor in meter(m). –A is cross-sectional area of the resistor in (m 2 ). –  is the resistivity of the material in (  -m)

IVE Resistivity Material  (  -m) at 0 o C Aluminium2.7x10 -8Aluminium2.7x10 -8 Brass7.2x10 -8Brass7.2x10 -8 Copper1.59x10 -8Copper1.59x10 -8 Carbon6500.0x10 -8Carbon6500.0x10 -8 Zinc5.57x10 -8Zinc5.57x10 -8

IVE Ohm’s Law Ohm's law states that the p.d. developed between the two ends of a resistor is directly proportional to the value of current flowing through it, provided that all other factors (e.g. temperature) remain constant V  I

IVE Ohm’s Law

IVE Resistors in Series

IVE Resistors in Series By Ohm's lawBy Ohm's law V 1 = IR 1 volts; V 2 = IR 2 volts; and V 3 = IR 3 volts E = V 1 + V 2 + V 3 E = I (R 1 + R 2 + R 3 )

IVE Resistors in Series E = IR eq and R eq = R 1 + R 2 + R 3 ohm where R eq is the total circuit resistance when resistors are connected in series the total resistance is found simply by adding together the resistor valueswhen resistors are connected in series the total resistance is found simply by adding together the resistor values

IVE Resistors in Parallel

IVE Resistors in Parallel By Ohm’s Law I 1 =E/ R 1 I 2 =E/ R 2 I 3 =E/ R 3

IVE Resistors in Parallel The total current of the circuit I is the sum of I 1, I 2 and I 3, thusThe total current of the circuit I is the sum of I 1, I 2 and I 3, thus I = I 1 + I 2 +I 3

IVE Resistors in Parallel The total resistance or the equivalent resistance(R eq ) of the circuit is defined to beThe total resistance or the equivalent resistance(R eq ) of the circuit is defined to be R eq = E/I

IVE Resistors in Parallel By substituting the above expression for the currents, we have E/R eq =I=E(1/R 1 +1/R 2 + 1/R 3 ) Thus we found 1/R eq =(1/R 1 +1/R 2 + 1/R 3 )

IVE Power in a resistive circuit Power is equal to the current multiplied by the voltage and the unit of power is watt (W)Power is equal to the current multiplied by the voltage and the unit of power is watt (W) P = IE

IVE Power in a resistive circuit By Ohm's law E=IR, the above equation can be modify to beBy Ohm's law E=IR, the above equation can be modify to be P = I 2 R Power is equal to the current squared, multiplied by the resistance.

IVE Power in a resistive circuit Use Ohm's law again, where I =E/R, we have P=E 2 /R Power is equal to the voltage squared, divided by the resistance.

IVE Example 1

IVE Example 1 –V AB + V BC + V CD is exactly equal to the emf=10V –The total resistance of the circuit is 2+5+3=10  –By Ohm's law V=IR, the current I should be equal to 1A

IVE Example 1 –V AB = IR AB =1 x 2 = 2V. –V BC = I R BC =1 x 5 = 5V. –V CD = IR CD =1 x 3 = 3V. –Power dissipation in R AB = I 2 R AB = 1 2 x 2 = 2W. –Power dissipation in R BC = I 2 R BC = 1 2 x 5 = 5W. –Power dissipation in R CD = I 2 R CD = 1 2 x 3 = 3W. –Total power dissipated = =10W

IVE Example 2

IVE Example 2 –the potential difference across each of the three resistors is equal to the battery emf 6V –Apply Ohm's Law –E=I 1 R 1 ; I 1 =E/R 1 = 6/2 = 3A –E=I 2 R 2 ; I 2 =E/R 2 = 6/3 = 2A –E=I 3 R 3 ; I 3 =E/R 3 = 6/6 = 1A

IVE Example 2 –The total current I is equal to the sum of currents I 1 +I 2 +I 3 = =6A. –Power dissipation in R 1 = I 1 2 R 1 = 3 2 x 2 = 18W. –Power dissipation in R 2 = I 2 2 R 2 = 2 2 x 3 = 12W. –Power dissipation in R 3 = I 3 2 R 3 = 1 2 x 6= 6W. –Total power dissipated = =36W

IVE Capacitance

Capacitance The property of a capacitor to store an electric charge when its plates are at different potentials is referred to as its capacitance(C). The unit of capacitance is farad(F)

IVE Capacitance The total charges stored in the capacitor (Q) is equal to the capacitance of the capacitor (C) multiplied by the potential across the capacitor(V).The total charges stored in the capacitor (Q) is equal to the capacitance of the capacitor (C) multiplied by the potential across the capacitor(V). Q = CV coulomb it is more usual to express capacitance values in microfarads (µF), nanofarads (nF), or picofarads (pF).it is more usual to express capacitance values in microfarads (µF), nanofarads (nF), or picofarads (pF).

IVE Charging of a RC circuit Switch S R C E VCVC I + -

IVE Charging of a RC circuit E Time, second Voltage across the capacitor, V C Charging current, I

IVE Discharging of a RC circuit Switch Discharge Current R C + - VCVC

IVE Discharging of a RC circuit Initial discharge current V c /R I Time, seconds Discharge current

IVE Energy Stored in Capacitance P.D (volt) V Charge (C) Q Area

IVE Energy Stored in Capacitance The area under the graph =QV/2The area under the graph =QV/2 But Q =CVcoulombBut Q =CVcoulomb so energy stored, W = CV 2 /2 joule so energy stored, W = CV 2 /2 joule.

IVE Capacitors connected in series D C D B A V3V3 V2V2 V1V1 C EQ A C1C1 C2C2 C3C3 VsVs VsVs +Q+Q +Q+Q+Q+Q +Q+Q

IVE Capacitors connected in parallel As Q, total charges stored on a capacitor = C 1 V 1 = C 2 V 2 = C 3 V 3 = V S C EQ or V 1 =Q/C 1, V 2 =Q/C 2, V 3 =Q/C 3 and V S =Q/C EQ and V S =V 1 +V 2 +V 3 = Q ( 1/C 1 +1/C 2 + 1/C 3 ) = Q/C EQ so, 1/C EQ = ( 1/C 1 +1/C 2 + 1/C 3 ) where C EQ is the equivalent capacitance of the capacitors in series.

IVE Capacitors connected in parallel +Q1+Q2+Q3 +(Q1+Q2+Q3) C1C1 C2C2 C3C3 C EQ VsVs VsVs

IVE Capacitors connected in parallel The voltage across the three capacitors = V S The charges stored on capacitor, C 1,Q 1 = V S C 1 The charges stored on capacitor, C 2,Q 2 = V S C 2 The charges stored on capacitor, C 3,Q 3 = V S C 3 Therefore, the total amount of charges stored = Q 1 +Q 2 +Q 3 = V S (C 1 +C 2 +C 3 )= V S C EQ ThereforeC EQ = (C 1 +C 2 +C 3 ) where C EQ is the equivalent capacitance of the capacitors in parallel

IVE Basic Concepts of electricity End