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DEPARTMENT OF PHYSICS

DEPARTMENT OF PHYSICS. ELECTRICAL CIRCUIT AND NETWORK SKILL COURSE CODE- PHYS205. PRESENTED BY: PROF. HEM CHAND. OBJECTIVES. To be able to identify and implement. Theory of Ohms Law. Define electrical terms.

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DEPARTMENT OF PHYSICS

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  1. DEPARTMENT OF PHYSICS ELECTRICAL CIRCUIT AND NETWORK SKILL COURSE CODE- PHYS205 PRESENTED BY: PROF. HEM CHAND

  2. OBJECTIVES To be able to identify and implement. Theory of OhmsLaw. Define electricalterms. To be able to describe the interrelationship between voltage, current and resistance in electricalcircuits. To be able to identify digital multimeter features and its capabilities. To be able to correctly use the digital multimeter and understand your findings when taking electrical measurements,in normal and fault findingsituations

  3. Basics ofelectricity • Types ofenergy- • - Electricalenergy • Heatenergy • Atomic energy • Mechanicalenergy • - One form of energy can be converted into another • OIL - Heat , Water - Steam , Turbine - Mechanical energy Generator - Electrical energy

  4. What isElectricity Matter PROTONS WITHINNUCLEUS ALL FORMS OF MATTER ARE MADE UP OFMOLECULES NEUTRONS WITHINNUCLEUS Molecule IN TURN THESE MOLECULES ARE MADEUP OF ATOMS ELECTRONS INORBIT ATOMS ARE MADE UP OFPROTONS ,NEUTRONSAND ELECTRONS. ELECTRONS MAINTAINA NEGATIVE POLARITY-ve Atom The centre of the atom is called theNucleus and contains Neutrons andprotons. PROTONS MAINTAIN A POSITIVE POLARITY+ve NEUTRONS DO NOT HAVE ANYPOLARITY (areneutral)

  5. What isElectricity Three factor determine whether or not the Atom is a good orbad CONDUCTOR (1) The number of electrons in the outerorbit. 2) The distance of the outer orbit from the Nucleus of theAtom. (3) The density of the atoms within theelement. Rules If the Atom has only one orbit,maximum number of electrons on orbit istwo. If Atom has more than one orbit maximum number of electrons on outer orbit iseight. Gold, Silver and Copper have only one electron on their outer orbit Mercury has two, Aluminium has three and remember Carbon hasfour. ELECTRONS INORBIT NUCLEUS

  6. What isElectricity COPPER ATOM ( good Conductor) 29 protons 29electrons. But only one loose electron On The outerorbit ELECTRONS INORBIT CARBON ATOM. 4 ELECTRONS ON THE OUTERORBIT (semiconductor) NUCLEUS PROTONS INNUCLEUS

  7. What isElectricity An excess of electrons creates a negative charge. The absence of electrons creates a positivecharge OPPOSITE CHARGES WILL ATTRACT EACHOTHER LIKE CHARGES REPEL EACHOTHER Normally an enormous number of Electrons flow.The basic unit of electric charge is thecoulomb. ONE COLOUMB EQUALS 6.25 X 1018 ELECTRONS,or6,250,000,000,000,000,0000 PROTONS INNUCLEUS ELECTRONS INORBIT

  8. What isElectricity Electronflow Conventionalflow load switch + - Anode\positive batterypost Cathode\negative battery

  9. Electronflow Conventionalflow load switch + - Anode\positive batterypost battery The loss of an electron by an atom makes it a positive ion, therefore it will attract an electron from a neighbouring atom,to again become balanced.

  10. Basics ofelectricity • Electricity- • There are variety of methods for producingelectricity • Through chemical reaction in abattery. • For large amount of electricity electromagnetic generators areused.

  11. Basics ofelectricity- • Current - • Flow ofelectron. • Conventional current is in oppositedirection. • High voltage to lowvoltage. • Unit of current isampere. • Current is measured by ammeter, Connected in series. • - Polarity inDC • 6

  12. Basics ofelectricity- • Potential - Ability to dowork • Voltage - Potential difference.(work done in moving a unit +ve charge from a pointof lower to higherpotential). • Unit of voltage is volt(v). • Measuredby voltmeter,connected acrosssource. • Sources can be Battery,DC generator,alternatoretc. • Can be AC orDC. • Polarity inDC • - Equivalent to two water tanks,connected by pipe water flows.

  13. FUNDAMENTALS OFELECTRICITY CURRENT VOLTAGE VOLTAGE = ELECTRICAL PRESSURE VOLTAGE Voltage provides the electrical pressure or force that enables the current or electrons toflow. Voltage is the difference in electrical pressure between two points in a circuit. Voltage is measured in units called volts . The symbol for Voltage is E and the symbol for voltis

  14. Basics ofelectricity • Resistance- • Opposes flow ofcurrent. • Unit isohms. • Measured by ohm meter connected acrossit. • Depends upon type of material, area &length. • Produces heat when current flows throughit. • Fixed and variable resistor(potentiometer). • 10

  15. FUNDAMENTALS OFELECTRICITY RESISTANCE RESISTANCE (OHMS). Resistance is a restriction to current flow. Increasing resistance will reduce flow ofcurrent. Electrical resistance is measured in units called ohms, they are abbreviated by the letter R, and the symbol is (omega). Amps electrons

  16. Basics ofelectricity • Inductor- • Coil ofwire. • Opposes change incurrent. • Used to create magnetic field forrotation. • - Unit ishenry. • - Open and shortinductor.

  17. Basics ofelectricity • Capacitor - • Two metal plates separated by a DI-electric (Max volts/mm which a medium can withstand withoutbreakdown). • Getschargedwhen voltage isapplied. • Unit of capacitance isfarad. • Capacitor in series 1/C=1/C1+1/C2 & in parallel C=C1+C2. • C = Q /V • Practical unitsMicro and Picofarad.

  18. Basics ofelectricity • Insulators and Conductors- • Conductors- • - Materials that have a low resistance to current flow are classified asconductors. • Copperandaluminium wires areconductors. • Conductors are used in electrical circuits to connect components to oneanother. • Conductors are wrapped in insulators to isolate from one another. • Insulators- • - Materials that haveahigh resistance to currentflow are classified as Insulators. • - Glass, rubber & dry air areinsulators • 13

  19. Basics ofelectricity Ohm’s law - Relation between three quantitieslearnt V= I xR I = V/ R R = V /I Where R = Resistance of circuit, inohms. V = Applied voltage, involts. I = Current, inamperes.

  20. OHMSLAW Ohms Law PieChart Resistance = Voltage overCurrent E I R E I R Current = Voltage overResistance voltage = Current timesResistance E I R E I R

  21. Basics ofelectricity- • DC power- • Power consumed in industry is almostA.C. • Power in DC circuit is P = V x I =I x R xI • Different types of load have different effect on powersource. • Unit of mechanical power ishorsepower. • 1 hp = 0.746kilowatts. • Measured bywattmeter.

  22. DCPOWER P APPLICATION OF THE POWERFORMULA. V I To find the power consumed by the resistor , the total current (I t) has to be foundfirst. It =Va\R1 It = 10 volts \ 10ohms +  R1 It = 1AMP. Va=10V - The power used by the resistor can then be found by: P = It xVt P = 1 amp x 10volts P = 10Watts

  23. DC POWER The unit of power in mechanical system isthe HORSE POWER(hp). P One horsepower isequalto 0.746 kilowatts(KW). TO CONVERT HORSE-POWER TOKILOWATTS. multiply horsepower times 0.746KW. EXAMPLE. P = Horsepower x 0.746Kw P = 50 Horsepower x 0.746Kw P = 37.3Kw Therefore a 50 Hp motor will consume 37.3 Kw ofpower

  24. Basics ofelectricity • ACPower- • Alternating quantity is one which periodically passes through a definite cycle ofchanges. • In AC RMS values are used. • AC power is consumed by different types of load such as inductive , resistive &capacitive. • AC power is given by P= V x I xCosO • Symbol for ACsource. • AC power is measured byWattmeter. • Unit of power isWatts. 18

  25. ELECTRICALTERM THE FOLLOWING TABLE SHOW SOME COMMON ELECTRICAL TERMS THEIR ABRIVIATION, UNITS OF MEASURE,SYMBOL AND MEASURINGINSTRUMENTS.

  26. Basics ofelectricity • Series circuit- • One path for current flow. • Can have more than one load (e.g.resistance). • Total load is sum of individualloads. • Some voltage loss takes place across each load and is called as voltagedrop. • Sum of voltage drops across each load is equal to appliedvoltage. • Current through each load issame. • Open andshort. • Example - Chain of smallbulbs. • 20

  27. OPEN AND SHORTCIRCUIT SHORT CIRCUITS occur when current does not go through its intended path.This usually happens in circuits that have improper wiring or defective electricalcomponents. In the diagram we have a series circuit in which R2&R3 are“shorted out” to the source voltage. R2 and R3look like a wire and the total resistance of thecircuit limited to R1. More nt will flow because the total resistance isless. current flows through the short. nocurrent flows through R2 orR3 current takes path of least resistance. R2 R3

  28. OPEN AND SHORTCIRCUITS If a short occurs in a parallel circuit , most of the source current will flow throughtheshort because the current takes thepath of leastresistance + R1 R2 R3 Most current will flows through short . no current will flow through R2 orR3

  29. FUNDAMENTALS OFELECTRICITY AMPERES SEVEREBURNS 6 AMPSTO SOLENOID 1.0 DEATH DIFFICULT BREATHING 0.2 200 mA OUCH! 0.01 100mA ITTINGLES 0.001 1mA CAN JUST FEELIT

  30. DIGITAL MULTIMETERDESCRIPTION. Measures ElectricalCharacteristics. Measures Multiple Types Of Electrical Characteristics with a single device. Functions as a Ohmmeter,Ammeter and Voltmeter. Includes an AC, as well as DC Voltagerange. Provides a Display “ Screen “. Includesoption for an analogformat. The accuracy of the fluke meter is specifiedas of the reading + ( number of least significant digits.) EG. Voltagedc

  31. D IGITAL MULTIMETER DESCRIPTION ROTARYSWITCH. To turn the meter on , turn the rotary switch from the OFF position . The meter performs a selftest , then starts takingreadings.

  32. DIGITAL MULTIMETERDESCRIPTION VOLTAGEMEASUREMENT Measure in parallelacross item to bemeasured Ranges 0 to1000 Volts dc 0 to 750 Voltsac

  33. DIGITAL MULTIMETERDESCRIPTION RESISTANCEMEASUREMENT Measure in parallel across item to bemeasured Ranges 320.0ohms thro 32.00Mohms.

  34. CURRENTMEASUREMENT Measure in serieswith item to bemeasured Ranges AC. 320 mAmps& 10Amps DC. 320 mAmps& 10Amps.

  35. DIGITAL MULTIMETERDESCRIPTION DIODETEST Measure in parallel across item to bemeasured Range 2 Volts dc. Continuitytest. Bleep while resistance isbelow 150ohms

  36. The ElectricalCircuit An electrical circuit can be compared to a simple hydrauliccircuit. Voltage drop(volts) Battery Ammeter Motor Amperes So urce ofpressure Flowrate Resistance toflow Pressure drop(bar) Liters /Min Pump Pump Flowmeter

  37. Basics ofelectricity- • Types of loads - (Resistor,inductor&capacitor) • Resistive load- • In DC circuit (fig) the voltage and current waveforms are straight lines because voltage isconstant. • In AC circuit with pure resistance,voltage and current are always in phase. • Power consumed in DC circuit is constantas voltage and current areconstant. • An AC ckt. thathas only resistance producesa positive power curve. 35

  38. Basics ofelectricity- • Types of loads - (Resistor,inductor&capacitor) • Resistive load- • In DC circuit (fig) the voltage and current waveforms are straight lines because voltage isconstant. • In AC circuit with pure resistance,voltage and current are always inphase. • Power consumed in DC circuit is constantas voltage and current areconstant. • An AC ckt. thathasonly resistance producesa positive power curve.

  39. Basics ofelectricity • Inductive load- • An inductor is a coil of wire. A commoninductive load is an electricmotor. • Current lag behind voltage by 900 since voltage is max at 900 while current iszero. • Produce both positive and negative power. These powers are equal in amplitude so their sum will equal tozero. • The inductor does not use real power stillgenerator supply it with voltage and current. • So efficiency islowered. 37

  40. Basics ofelectricity • Capacitiveload- • A capacitor opposes change involtage. • Current lead voltage by 900 since voltage across it is zero and the current is maximum. • Produce both positive and negative power. These powers are equal in amplitude so their sum will equal tozero. • Thecapacitor does not use real power stillgenerator supply it with voltage and current. - So efficiency islowered. 39

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