DC Fundamentals Series Resistive Circuits Exercise 2: Current in a Series Resistive Circuit EXERCISE OBJECTIVE circuit by using a formula. You will verify your results with a multimeter. DISCUSSION Electric current is the movement of electrons between two points (A to B) in a circuit. When components are connected end-to-end to form a series circuit, electrons leave the negative In a series string, what is the relationship between circuit current and the distribution of that current through each resistor of the string? a. The current through each resistor is the same and equal to the total circuit current. b. The current through each resistor varies in direct proportion to the value of the resistor. c. The current through each resistor varies in inverse proportion to the value of the resistor. a voltage drop. How can the voltage drop of a resistor be used to determine total circuit current? a. Individual voltage drops cannot be used to determine total circuit current. b. Use I T = V R x R. c. Use I T = V R /R. FACET by Lab-Volt 131
Series Resistive Circuits DC Fundamentals PROCEDURE Locate the SERIES CIRCUIT circuit block, and connect the circuit shown. Measure the value of the voltage source. V A = Vdc (Recall Value 1) 132 FACET by Lab-Volt
DC Fundamentals Series Resistive Circuits Calculate the total resistance of your circuit. Use the nominal color code values for each resistor. R T = (Recall Value 2) Based on an applied source voltage of Vdc (Step 2, Recall Value 1) and circuit resistance of (Step 3, Recall Value 2), calculate the circuit current. NOTE: I T = V A /R T I T (or I R1 ) = ma (Recall Value 3) FACET by Lab-Volt 133
Series Resistive Circuits DC Fundamentals Use the measured voltage drop of R1 to determine circuit current (I T = V R1 /R1). NOTE: Use the nominal value of 1000 for R1. I T (or I R1 ) = ma (Recall Value 4) Your calculated total circuit current is ma (Step 4, Recall Value 3). The circuit current based on the voltage drop across R1 is ma (Step 5, Recall Value 4). Do the a. Yes. The current in a series circuit is the same throughout the circuit. b. No. The current in a series circuit need not be the same throughout the circuit. c. No. The current in a series circuit varies according to the values of the resistors in the string. ma (Step 4, Recall Value 3)? a. The circuit current increased because circuit resistance decreased. b. No change occurred in the circuit because circuit voltage did not change. c. The circuit current decreased because circuit resistance increased. CM 2 is still activated. The resistance of R2 is changed. What effect does this change have on the circuit current? a. None, since only one resistor is changed. b. The circuit current must change. c. None, until a matching voltage change is made. Make sure all CMs are cleared (turned off) before proceeding to the next section. 134 FACET by Lab-Volt
DC Fundamentals Series Resistive Circuits CONCLUSION Circuit current is determined by the voltage source and the total circuit resistance. When total resistance decreases, circuit current increases. When total resistance increases, circuit current decreases. In a series resistive circuit where the voltage is held constant, the circuit current is inversely proportional to the resistance. REVIEW QUESTIONS 1. In a series circuit, the current is a. greater in the larger resistors. b. the same in all parts of the circuit. c. greater when total resistance increases. d. inversely proportional to the voltage source. 2. When you connect an ammeter into a dc circuit, a. the ammeter is connected in series with the circuit. b. polarity is not important. c. the ammeter is connected in parallel with the circuit. d. the RED lead is connected to the most negative point in the circuit. 3. On the SERIES CIRCUIT circuit block, connect the circuit shown. Place CM switch 2 in the ON position. Which component caused the circuit current to change? a. R1 increased in value. b. R2 increased in value. c. R3 increased in value. d. The voltage source decreased in value. 4. In this circuit, if R1 changed in value to 2 k, the a. current through R1 would be 5.3 ma. b. total resistance would be 3620. c. total circuit current would be 4.3 ma. d. current through R1 would be 3.9 ma. FACET by Lab-Volt 135
Series Resistive Circuits DC Fundamentals 5. An increase in the current of a series circuit can be caused by a a. proportional increase in voltage and resistance. b. voltage decrease and resistance increase. c. resistance decrease. d. voltage decrease. NOTE: Make sure all CMs are cleared (turned off) before proceeding to the next section. 136 FACET by Lab-Volt