# LABORATORY relationship between V, I and R is

LABORATORY MANUAL FOR ELECTRICALMEASUREMENTEEC 126 PREPAREDBY   ODUBONAISMAIL OKANLAWON  DEPARTMENTOF ELECTRICAL/ELECTRONIC ENGINEERINGYABACOLLEGE OF TECHNOLOGY.            TABLEOF CONTENTSEXPERIMENTONEOhm’slaw EXPERIMENTTWOKirchhoff’s voltage law (KVL) EXPERIMENTTHREEKirchhoff’scurrent law (KCL) EXPERIMENTFOUROscilloscope EXPERIMENTFIVEMeasurement of power EXPERIMENTSIXMeasuringcurrent and voltage EXPERIMENTSEVENAmmeterconversion EXPERIMENTEIGHTVoltmeterconversion   EXPERIMENTNO: ONETITLE:OHM’S LAWOBJECTIVEAt the end of this experimentstudent should be able to verify Implementationof the Ohm’s law. APPARATUS1.     Variabled.c power supply unit2.

DecadeResistance boxes3.     Digitalmultmeter. THEORYOhm’s law states that in a closed circuit, thevoltage across a resistor is directly proportional to the current flowing init, i.e V a ITherelationship between V, I and R is stated by the following Ohm’s Law:                                          DIAGRAM         PROCEDURE       1.     Connectthe circuit as shown in the diagram.

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Choose 1k resistor from the resistor bank.2.     Switchon the variable power supply and vary the voltage from zero to 10V in step of1V.

3.     Recordthe voltage steps and the corresponding value of current in a tabular form.4.     Repeatthe experiment for values of resistors to be 5k and 10k5.     Repeatthe experiment for a value of an unknown resistor6.     Onthe same graph sheet, plot the graphs of voltage against current for all the experiments.7.

Determinethe slop of each graph and compare with the values of the resistors.8.     Usinga digital multi-meter read the value of the unknown resistor and compares thevalue with the slop of the unknown resistor graph.RESULTWith 1k resistor Volt(V) 0 1 2 3 4 5 6 7 8 9 10 Current (mA)                        With 5k resistor Volt(V) 0 1 2 3 4 5 6 7 8 9 10 Current (mA)                           With 1k resistor Volt(V) 0 1 2 3 4 5 6 7 8 9 10 Current (mA)                       With 10k resistor Volt(V) 0 1 2 3 4 5 6 7 8 9 10 Current (mA)                        With unknown resistor Volt(V) 0 1 2 3 4 5 6 7 8 9 10 Current (mA)                        Gradient = ?V/?ICONCLUSION1.     Identifyif the graph is a straight line.2.

Statethe result of the comparison of results3.     Concludeif ohm’s law is verified.       EXPERIMENTNO: TWOTITLE:Verification of Kirchhoff’s voltage law (KVL)OBJECTIVE:At the end of this experiment, students should be able to: 1. Understand the concept of voltage division and2. Verify Kirchhoff’s voltage law (KVL)APPARATUS1                A multimeter2                Variablepower supply3                Milliameter4                Decaderesistor bank  THEORYWhen resistors are connected in series in a closedcircuit, the source voltage is divided among the resistors, while the samecurrent flows in the resistors i.e. VS = VR1 + VR2 + VR3+ ……VRN.  = IR1 +IR2 + IR3 + ……IRN                =I(R1 + R2 + R3 + ……RN)I = VS/(R1 + R2 + R3+ ……RN)V1 = VSR1/(R1+ R2 + R3 + ……RN)V2 = VSR2/(R1+ R2 + R3 + ……RN)V3 = VSR3/(R1+ R2 + R3 + ……RN)VN = VSRN/(R1+ R2 + R3 + ……RN)Kirchhoff’s voltage law states that in a closedloop, the algebraic sum of voltages equals zero.

In a simple word if the loopis an active loop, the sum of voltage drops across the loop elements is equalto the voltage of the source.VS = V1 + V2 + V3+ ……VN  DIAGRAM        PROCEDURE1.     Connectthe circuit as shown in the diagram.2.     Switchon the power supply and adjust the voltage to 12V3.

Measurethe voltages across R1, R2, and R3.4.     Measurethe current in the circuit.5.     Measurethe voltage of the source.6.     Addall the values of voltages across the resistors and confirm if equal the tosource voltage.7.

Dividethe voltage across each resistor by the value of the resistor and compare ifthey are equal to the measured current.RESULTVR1 = ………VR2 = ………VR3 = ………I = …………VS = ………..VR1 + VR2 + VR3 =……… V/R1 = ……..

V/R2= ……. V/R3= ……… CONCLUSION1.     Whatis the result of your comparisons2.     Establishif Kirchhoff’s voltage law is confirmed.                EXPERIMENTNO: THREETITLE:Verification of Kirchhoff’s current law (KCL)OBJECTIVE:Students are expected to understand that resistors connected in parallel sharecurrent among themselves depending on the values of their resistance. Thisconcept establishes the Kirchhoff’s current law which states that the algebraicsum of current at a node in an active circuit equals zero, i.

e. the totalcurrent entering into a node equals the total current flowing out of the node. APPARATUS1.     A multimeter2.     Variable power supply3.     Milliameter 4.

Decade resistor bank THEORYWhenresistors are connected in parallel current is shared among them while the samevoltage appeared across themConsider node A in the figure shown,The sum of the current at the node=  I – I1– I2 = 0I = I1 + I2The source current Iis divided to I1 and I2. VR1= VR2 = V DIAGRAM     PROCEDURE1.     Connectthe circuit as shown in the diagram2.     SwitchON the power supply and set the voltage to 10V3.     Measurethe readings of the ammeters and the voltmeter.4.     Recordthe values measured and switch OFF the power supply.

RESULTMeasured valuesI = ……..I1 = ……..

I2 = ……..V = ……….I1 + I2 = ………. Compare if (I1 + I2) equals IImplement  I1+ I2 – I Calculated valuesI1 = V/R1 = ……….I2 = V/R2 = ……….I = V/R1R2/(R1 + R2)Compare (I1 + I2) to I.

Implement  I1+ I2 – I CONCLUSION1.     Provefrom the result if resistors in parallel share current.2.

Determineif KCL is verified3.     Commenton any variation in the result.EXPERIMENT FOURTITLE: OSCILLOSCOPEObjectivesAfter thecompletion of the experiment, students are expected to know how to useoscilloscope to:·       Measure voltage·       Frequency·       Study waveform THEORYThe oscilloscope, or scope forshort, is a device for drawing calibrated graphs of voltage vs time veryquickly and conveniently. Such an instrument is obviously useful for the designand repair of circuits in which voltages and currents are changing with time.A ‘scope’ samples the voltage anddisplays it on a screen that is marked with a grid in centimetres.

From thevertical gain in Volts/cm we can measure the amplitude of the signal in Volts,and from the horizontal scale in sec/cm (the ‘timebase’), we can measure thetiming of that signal. Scopes always have two or more channels so that the relativetiming or amplitude of two signals can be compared.The front panel, shown in Fig. 1,is correspondingly formidable at first glance.

Equipment:·       A dual traceoscilloscope·       Funcion generaors·       Multimeter Procedure:Step 1:       power up the oscilloscope and the signal generators.Step 2:       set the oscilloscope sweep to 2µs and the volt/div to 2VStep 3:       connect the signal generator to channel 1 of the oscilloscope.Step 4:       set the signal generator to sine wave with frequency of 1khzand the amplitude measured with multimeter to 6VStep 5:       adjust the trigger on the oscilloscope until a stable trace isachieved.RESULT1.

Draw the trace on a paper 2. Measure the amplitude of thetrace          Numberof vertical division x volts per division3. Compare the multimeter with thatof the oscilloscope4. Comment on the difference5. Measure the frequency of thewavePeriod (T) = Number of horizontaldivisions x sweep.Frequency = 1/T.6. Compare the oscilloscope readingto the setting of the signal generator.

EXPERIMENT FIVETITLE: MEASUREMENT OF POWERObjective: students are expected to know how to use a wattmeterat the end of his experiment.Theory: Watt meter is an instrument used for the measurement ofpower. It is basically composed of two coils (the current and the voltagecoil). The interaction of magnectic fields produced by the two coils isresponsible for the deflection of a pointer which moves over a calibrated scaleand the reading corresponds to the power delivered to the circuit in which thewatt meter is being connected.Apparatus:·      Watt meter·      20W 50? rheostat·      DC power supplyDiagram     ProcedureStep 1:           connect the circuit as shown in thediagramStep 2:           connect the current coil of the wattmeter marked I in series with the load and the voltage coil marked V inparallel with the load.

Step 3:           adjust the DC power supply to 12V andswitch ONStep 4:           record the watt meter reading RESULTCalculate power P = V2/RCompare the reading of thewatt meter and the calculated value to the wattage marked wattage on therheostat.Comment on the results                   EXPERIMENT SIXTITLE: MEASURING CURRENT AND VOLTAGE Objective: At the end of this experiment, students are expectedto know how to:·      Connect ammeter to measure current·      Connect voltmeter to measure voltageTheory: ammeters are constructed using Galvanometers of very lowinternal resistance so that the meter will have negligible voltage drop whichmay affect the overall drop across the load. However, volt meters areconstructed to have high internal resistance so that the meter resistance willhave negligible effect on the overall resistance.Apparatus:·      Ammeter 0 – 10A·      Voltmeter 0 – 50V·      DC power supply.·      20W 50? rheostatDiagram:1.      2.

Procedure:Step 1:       connect the ammeter in series with theRheostat and to the DC power supply as shown in the fig. 1 aboveStep 2:       set the DC power supply to 12V and switchON the powerStep 3:       measure and record the current on theammeterRESULTUsing I = V/R calculate thecurrent           V = 12V and R = 50?Compare the measured currentwith the calculated currentComment on the result. Step 4:       connect the voltmeter in parallel withthe rheostat and to the DC power supply as shown in fig.

2Step 5:       with DC power supply at 12V switch ONStep 6:       measure and record the voltage across therheostatStep 7:       remove the rheostat and measure thevoltage across the DC power supplyRESULTCompare the measured voltagewith rheostat to measured voltage without rheostat.                    EXPERIMENT SEVENTITLE: AMMETER CONVERSIONObjective: At the end of this experiment students are expected toknow how to convert ammeters to measure higher current than the rated current. Theory: Ammeterscan be used to measure higher current by connecting shunt resistor across it.Apparatus:·      10mA ammeter·       1? rheostat·      20? rheostat·      Variable DC power supply 0 – 30V, 5ADiagram      ProcedureStep 1:           connect the circuit as shown with theshunt switch openStep 2:           switch ON the power supply and adjustthe voltage until full scale deflection is reached. Record the voltage value (VO)and the full scale current (IO)  Step 3:          closethe shunt resistor switch and gradually reduce the resistance until the currenton the ammeter reduce to 1mA.Step 4:           now increase the voltage of the powersupply until full scale deflection is reached.

Also take the voltage reading (VS)  RESULTCalculate (r + R) = VO/IO………..(1)Where r = meter resistance            R = Rheostat resistanceFind rCalculate Vr = IOr…………….(2)Calculate (r//rS)+ R = VS/1A …………….(3)            rS = Vr/(1 – 0.1)rS = value ofshunt resistorCalculate (r//rS)+ R and compare result with (3)              EXPERIMENT EIGHTTITLE: VOLTMETER CONVERSIONObjective: At the end of this experiment students are expected toknow how to convert voltmeters to measure higher current than the ratedcurrent.

Theory: Voltmeterscan be used to measure higher voltage by connecting resistor in series with it.Apparatus:·      Voltmeter 0 – 10V·       100K? pot.·      20? rheostat·      Variable DC power supply 0 – 30V, 5ADiagram           ProcedureStep 1:           connect the circuit as shown with theswitch closedStep 2:           switch ON the power supply and adjustthe voltage until full scale deflection is reached. Record the full scale voltagevalue (VO)  Step 3:          openthe switch and gradually increase the resistance until the voltage reduce tohalf full scale defection (5V).

Step 4:           now increase the voltage of the powersupply until full scale deflection is reached. Step 5:           disconnect the circuit and measurethe resistance of the pot that was connected to the circuit, RP  RESULT         RP   Before the connection of RP (i.e.

switch closed)all 10V is across the meter (Rm) and by opening the switch andadjusting RP for deflect to reduce to 5V, RP at thatpoint equals Rm.i.e. RP = Rm.= Rand VRP = VRm= Vwhere V is the voltmeterreading.Therefore the supply voltageequal 2VThe measured resistancetherefore multiplies the meter reading by two (x2)Repeat the experiment with step3 reducing to 3.3V and determine the multiplying value.