EETQ 114 Lab 3 - Series Circuits

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Centennial College *

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EETQ114

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Electrical Engineering

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Jan 9, 2024

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Page 1 of 4 Centennial College Electrical Engineering Technician / Technology EETQ-114 Electronics 1 and Instrumentation 1 Name: Student #: Section: Date: LAB #3 Series Circuits Objectives: • Use Ohm's law to find the current and voltages in a series circuit. • Apply Kirchhoff's voltage law to a series circuit. Theory: The current in a resistor is directly proportional to the voltage across the resistor as stated by Ohm's law. Consider the simple circuit illustrated in Figure A . The source voltage is the total current multiplied by the total resistance. This can be stated in equation form as: 𝑉 ? = 𝐼 ? 𝑅 ? Figure A Figure B In a series circuit, the circuit elements are connected together with only one path for current. Figure B illustrates a series circuit with two resistors. When we join resistors in series, the total resistance is the sum of the individual resistors. The total resistance for the circuit in Figure B is: 𝑅 ? = 𝑅 1 + 𝑅 2 Substituting this equation into Ohm's law gives: 𝑉 ? = 𝐼 ? (𝑅 1 + 𝑅 2 ) Multiplying both terms by IT results in: 𝑉 ? = 𝐼 ? 𝑅 1 + 𝐼 ? 𝑅 2

Page 2 of 4 The identical current, IT, must flow through each resistor. This causes a voltage drop across each resistor, which can be expressed as: 𝑉 ? = 𝐼 ? (𝑅 1 + 𝑅 2 ) This result illustrates that the source voltage is equal to the sum of the voltage drops across the resistors. This relationship illustrates Kirchhoff's voltage law, which is more precisely stated as: “ The algebraic sum of all voltage rises and drops around any single closed path in a circuit is equal to zero . ” It is important to pay attention to the polarity of the voltages. Current from the source creates a voltage drop across the load. The voltage drop across the load will have an opposite polarity to the source voltage, as illustrated in Figure B . We may apply Kirchhoff's voltage law by using the following rules: 1. Choose an arbitrary starting point. Go either clockwise or counterclockwise from the starting point. 2. For each voltage source or load, write down the first sign you see and the magnitude of the voltage. 3. When you arrive at the starting point, equate the algebraic sum of the voltages to zero. Equipment: • Breadboard • Variable DC Power Supply (BK Precision 1672) • Alligator test leads • DMM (Keithley 2110) • Resistors: 47 Ω, 100 Ω, 270 Ω, and 330 Ω Procedure: 1. On your breadboard, build the circuit illustrated in Figure 1 . Connect the resistors in series. 2. Using the colour coded values of resistance, determine the total resistance of the circuit. Calculated Total Circuit Resistance = ___________________ Ω 3. With the power supply still OFF and disconnected from the circuit, measure the total resistance of the circuit between the input leads ( Figure 2 ). Measured Total Circuit Resistance = ___________________ Ω 5 Figure 1 Figure 2 – R T measurement 4. Using the measured total resistance value from Step 3, determine the current that would be flowing through the circuit if the supply voltage (V S ) is 10 v . Calculated Current Flow = ___________________ A 5. Complete the circuit shown in Figure 3 , making sure that the DMM is in the voltmeter setting. Turn ON the Power Supply and set the supply voltage (V S ) to 10 V .

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