DC circuits

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Northeastern University *

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1146

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Electrical Engineering

Date

Apr 3, 2024

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docx

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Uploaded by mr.ikeepitreel

Report for Experiment #17 DC circuits Introduction: In this lab simple electric circuits are studied and examined closely. Electric circuits work as they have a flow of current moving through them, current can be described as the flow rate of charge past a certain point per unit of time. The following equation describes this relationship:

I = ΔQ / Δt (17.1) Apart from these circuits are varying amounts of resistance (resistance to charge flow) and voltage potential (electrical tension due to varying amount of charge). To create an electric circuit a close wire loop must be attached to opposing sides of a current source/battery as charge flow is a result of opposing voltage values due to the opposite terminal of charges in the battery source. A battery that is not however in a closed loop maintains an electromotive force (emf) due to the voltage difference between two terminals, this value is constant in this case. This value of emf describes the amount of work done to charge in moving charges from one terminal to another, the following equation shows this relationship: ε = ΔW / Δq (17.1) Resistance to the flow of charge as mentioned briefly is properly known as resistance (R), and it can be described as the ratio between the change in voltage and current. This ratio is known as ohm's law where volts/amp is measured in ohms (Ω). Lastly the amount of energy/ time or work per unit time a circuit does is known as the power of the circuit, using ohm's law it can be further simplified to obtain new relationships. The following equations describe these relationships: P = ΔW / Δt = I 2 R (17.4) There are rules that govern the currents and voltages that run a circuit, and they are Kirchhoff's rules. The first one, the loop rule, dictates that the sum of all voltage differences in a closed circuit is zero. The second rule, the junction rule, dictates that the sum of all currents flowing into a junction must be zero, in other words what goes in must come out. The goal of this lab along with understanding the elements of a circuit is to measure currents, and voltages using digital multimeters and apply kirchhoff's rules of circuits to analyze and test different circuits. In investigation 1 the voltage across batteries in parallel and in series and alone are measured to understand voltage differences due to the combinations. In investigation 2 ohmic resistance is thoroughly analyzed and ohm's law is applied to calculate resistance and internal resistance is found. In investigation 3 two resistors in series and in parallel are studied as kirchoff's rule are applied and the current and power for both circuits are experimentally found. Studying these fundamental rules is crucial to understanding circuits, this is important as all electronics function in some shape or form due to circuits. Investigation 1: Electromotive force of Battery combinations To begin this investigation first the DMMs device was inspected thoroughly, next the voltage across a single battery was measured using the device. The DMM was connected as a voltmeter across the battery and cables were used to attach the positive battery end to the terminal and the negative end to the other negative terminal. The proceeding voltage measurement was then recorded on excel, next two batteries were attached to each other in series and the voltage once again measured and recorded separately. Lastly the batteries were connected in parallel using more cables, and the voltage across this circuit was measured and recorded.

Data table for investigation 1: V one battery voltage 1.324 one battery voltage 1.554 two battery voltage series 2.887 two battery voltage Parallel 1.437 Investigation 2: Ohmic resistance To begin this investigation the DMM was set to an ohmmeter to measure and record resistance. Using a circuit element box for resistors the 100 ohm resistor was measured using the ohmmeter, the actual value for resistance for this resistor was recorded on excel and the value was within tolerance. Next the emf of one of the batteries was measured, this battery was used for the rest of the investigation. A circuit was then made to measure the current through the 100 ohm resistor connected in series with the battery. To do so one of the DMMs was set up to be an ammeter, and the current was measured and recorded. Next the second DMM was added to the circuit and set as a voltmeter to measure the voltage across the resistor. From the values of current and voltage that were measured using ohm's law the experimental value for resistance was calculated. Next the voltmeter was disconnected and re attached to measure the voltage across current meter to get the value for burden on voltage. Lastly the results from this investigation was used along with equation ΔV source = ε − I ∗ r (17.13) to find the internal resistance, r, of the battery. These values were recorded in excel. Data table for investigation 2: emf V 1.34 resistance 100.29 I (mA) 13.303 V( with R) 1.325 Calc R value 99.60159363 V without R 14.5

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