How to Understand Electrical Circuitry

Experimental Objectives 

The performance of this experiment was based on the object of understanding electrical circuitry and concepts with a simple circuit constructed using a resistor, jumper cables and a battery pack. Secondly, the experiment is aimed at familiarizing with the use of a multi-meter in measuring the potential difference, current and resistance. Finally, the experiment is objected to testing the validity of Ohm’s law. 

Experimental Materials/Equipment 

The performance of this lab experiment was guaranteed a success with the input of the following materials: 3 pieces of AA battery-1.5V, 3 battery holders, a digital multi-meter, 5 jumper cables, a resistor that can provide 100Ω resistance, a pair of safety goggles, a digital camera/smartphone, a pencil/pen and a sheet of paper. 

Theory 

The electrical circuitry system is very ubiquitous in our daily lives. Ohms law is a very basic and important relationship or concept that makes us understand about electric current, potential difference and resistance across transmission materials. Therefore, the Ohms law describes the relationship between the three variables for most Ohmic conductors. Potential Difference, commonly referred to as the voltage offers an electromotive force that moves charge around a circuitry loop. Voltage is potential energy per unit charge and is quantified in Volts (V). Electrical current refers to the rate of flow of electrical charge past a given point in a circuit. Current (I) is quant5fied in Amperes (A). Resistance (R) refers to the measure of opposition to the flow of current within a circuit. It is quantified in ohms (Ω). 

The Ohms law equation is a simplified relationship that relates voltage, current, and resistance. It proceeds as ; V- voltage, I- Current, R-resistance. The equation shows that potential difference is directly proportional to current and current varies inversely with resistance. The usefulness of Ohms law comes in the moderation of any of the three variables to achieve the desired threshold. It is important in the quantification of electrical power which is the rate of energy flow per unit time; P=IV. 

The materials which obey Ohms law are known as Ohmic conductors and they display a linear relationship between current and voltage with a constant of proportionality as the resistance. Non-Ohmic conductors, on the other hand, do not obey ohms’ law and they depict a non-linear relationship. 

Figure 1: Ohmic & non-ohmic material relationships 

In summary, therefore, Ohms law states that the Voltage (V) across a circuit is directly proportional to the current (I) that flows though the circuit and resistance (R), that is V=IR. As such, an increase in voltage results in an increase in current given that resistance remains constant. 

Different symbols are conventionally accepted for circuit diagrams. Below is a table of the basic circuit diagram symbols, some of which have been used in the present experiment. 

Figure 2: Circuit Diagram Symbols 

Computing Resistor Values 

In order to obtain a resistor value based on their strip color configuration, the first strip is identified as gold/silver whose indication should be known. The second and third color strips are read from the table given below. The values of the second and the third strips are multiplied by the value of the first strips giving resistance in Ohms. The fourth strip is the tolerance value. 

Figure 3: Resistor Color Coding 

Procedure for Testing Ohms Law in A simple circuit 

The experiment involves the construction of a simple circuit and then using a digital multi-meter in order to measure the voltage and current within the circuit under different configurations of the circuit battery were Ohms law is then used to calculate circuit resistance. 

Part 1: Measuring Resistance 

The DMM was set for use as an ohmmeter with a dial range of 2KΩ whereby the resistance of all resistors was quantified and recorded. The circuit that was used had 1.5V battery, 100Ω resistor, 3-jumper cables as shown below. 

DMM (b) Simple Circuit &Real Construction (c) Measuring resistance on DMM 

Part 2: Measuring Current 

The meter is set as an ammeter with the dial range in mA. The jumper cable with the help of alligator clips was used to connect to the negative terminal of the battery. The other end of the resistor is connected to the black lead of the multimeter. The positive end of the battery was then plugged into the red lead of the meter. In order to ease the measurement of current, all connection was propagated in series while for the potential difference, the arrangement was made in parallel. All current readings from the meter were recorded in milli Amperes through different points of the circuit. 

Figure 4: Measurement of Current using the multi-meter 

Part 3: Measurement of Potential Difference 

The Multi-meter was removed from the circuit by disconnecting the alligator clips ends of the jumper cables ten the circuit is closed without the multi-meter. The multi-meter is set on a dial range of 20V. It s then connected parallel to the circuit with the red lead terminal of the meter to the positive end of the battery and the black-led to the negative end. 

Figure 5: Circuit diagram for measuring the potential difference 

Further, the multi-meter leads are reversed and the observations recorded. The voltmeter is again set between the positive battery terminal and the resistor and the terminals are again reversed. Another connection is made where the two resistor ends are reversed and observations are made. 

Figure 6: Circuit diagrams for Current and Potential difference with 2-batteries connected. 

With the same procedure, a connection of three batteries is done and the current and potential difference measured and data tabulated for circuit 3 in table 3. 

Figure 7: 3-battery configuration/Circuit 3 

All current readings were converted into Amperes (1A=1000mA) and the data tabulated. The resistance (R) for each circuit was computed using Ohms law (R=V/I). 

Results 

Table 1: Measured Resistance
Resistor: 100Ω	Measured Resistance 99.3Ω

Table 2: Current & Potential Difference of Simple Circuits
	Current(mA)	Current (A)	Potential Difference (V)	Calculated Resistance (Ω)
	200mA	15.10A	1.52V	100.67 Ω
	200mA	29.60A	3.10V	104.73 Ω
	200mA	48.15A	4.84V	100.52 Ω

Discussion 

Ohms law is best defined as the total value of the current flowing through and between a two-pint conductor in a given circuit and directly corresponds to the voltage across the circuit for a constant temperature. For instance; if for two points A and Z are the ends of a conductor, the potentials at A and Z are equal to Va and Vz. The current that ill pass from point A to Z through the conductor I; (Va-Vz)I or Va-Vz =Ri. Va-Vz =V and thus V=IR or I=V/R where R- is the conductor resistance, V-potential difference and I- current that flows through the conductor. R is a constantan it is the resistance of the ohmic conductor used in the experiment. The resistor used has a stated manufacturers tolerance of (-/+ 5%), but the measured resistance read 99.3 Ω instead of the indicated 100 Ω which signified that the actual resistance can vary within 95-105 Ω which was the reason why our results mirrored around the manufacturer’s statement of tolerance. 

The results in the table indicated the potential difference across the battery where the meter leads, jumper cables were integral for the flow within the circuit. The current that was initiated from the positive terminal flowed towards the negative end. The potential difference that was retrieved was 15.1A when the multi-meter indicated 200m A and a potential difference of 1.52V was obtained. The resistance was then obtained as follows R=V/I giving 100.67 Ω. For all the circuits, the current entering the battery was equal to the sum current leaving the junctions irrespective of how much load was there. The jumper cables offered no quantifiable resistance which could affect the results. 

Figure 8: Ohms law relationship 

Slope= Resistance 

The results in table two produced a linear relationship which indicated that the materials of the jumper cables were ohmic and that the results were in agreement with Ohms law. Employing the use of a higher resistance resistor results in a decline in the value of current but the potential difference would remain constant. 

Conclusion 

The object of this experiment was to validate Ohms law via the construction of simple circuit systems. It is true that Ohms law was verified with a linear relationship established between current and potential difference with a constant of proportionality known as the material’s resistance. The Digital Multi-meter can be used as an ammeter, voltmeter or even an ohmmeter with careful selection of scales.