DC Series Circuits Explained: Voltage, Current, Resistance, and Power with a Multimeter

Overview

In this Engineering Mindset lesson, Paul explains DC series circuits focusing on voltage, current, resistance, and power. The video walks through the behavior of resistors in series, how to calculate total resistance, how current is the same through all components, how voltage divides across each resistor, and how to use a multimeter to test readings. Real-world examples with LED lights illustrate how resistance affects current and brightness, and power calculations show where energy goes as heat. The lesson ends with a knowledge-check on a 9V LED-resistor circuit.

Introduction to DC Series Circuits

The video begins by situating series circuits within the broader context of how components can be connected in electrical networks. Paul emphasizes that in a series connection there is only a single path for electrons to flow, so all components carry the same current. He uses electron flow animations to illustrate this, noting the distinction between electron flow (negative to positive) and conventional current (positive to negative).

Key Quantities: Voltage, Current, and Resistance

The tutorial then defines the core electrical quantities. Resistance, measured in ohms, opposes applied voltage. In a series circuit, total resistance is the sum of each component’s resistance, and the total resistance is denoted as R_T. Paul walks through simple examples: a single 10 ohm resistor yields R_T = 10 ohms; adding a 5 ohm resistor makes R_T = 15 ohms, and so on. He notes that wires add a small amount of resistance in real circuits, though often negligible.

Current in Series Circuits

Current is the flow of electrons and is measured in amperes or amps. In a series circuit the current is identical at all points because there is only one path for the electrons to travel. Paul explains that the position where you measure the current does not affect the reading, as long as you are measuring through the same single path.

Voltage in Series Circuits: Voltage Division

Voltage represents the pushing force on electrons. In a series circuit, the total voltage from the source is divided among the resistors according to their resistance. The video demonstrates this with a 9V source across multiple resistors. For example, across a 10 ohm resistor in a two-resistor series (10 ohms and 10 ohms) the voltage drop is 9V across the pair but only 4.5V across each resistor. The text shows how different resistor values lead to different voltage drops, while the current remains the same throughout the circuit.

Power in Series Circuits

Power consumption is discussed in terms of P = V^2 / R or P = V x I. Since resistors convert electrical energy into heat, power dissipated equals heat produced. The video provides concrete calculations for circuits with a 9V source and different total resistances, showing how power drops as resistance increases, consistent with the voltage and current relationships in series circuits.

LED Demonstrations and Practical Design

To visualize the effect of resistance on current, Paul connects an LED with a resistor to a 9V battery. He illustrates safety by comparing different resistor values (for example, 100 ohms, 450 ohms, 900 ohms) and notes the corresponding LED brightness. He also discusses using resistors to protect components by limiting current, explaining why too much current can damage an LED and how higher resistance dims the LED as current decreases.

Measuring with a Multimeter

The video covers how a multimeter can be used to read current and voltage in the circuit, highlighting that the meter itself introduces a small resistance, which is usually negligible for practical purposes. The tutorial reinforces the importance of understanding how to place meters in a circuit to measure current and voltage accurately.

Worked Examples and Knowledge Check

Several worked examples are presented: a 9V battery with a single resistor (R1 = 10 ohms) yields a current of 0.9 A and voltage drop of 9V across the resistor; adding a second resistor (R2 = 5 ohms) changes the current to 0.6 A with voltage drops of 6V and 3V across R1 and R2, respectively; adding a third resistor (R3 = 5 ohms) yields a total current of 0.45 A with voltage drops of 4.5V, 2.25V, and 2.25V. Paul emphasizes that these relationships confirm the total voltage drop equals the source voltage and the sum of individual drops equals the total current times resistance.

The LED knowledge-check question asks viewers to estimate the current in a circuit with a 9V source and LEDs constrained to 0.02 A. A link in the description provides the answer, inviting viewers to apply the concepts covered in the video.

Conclusion and Next Steps

The video wraps up by pointing viewers toward further tutorials and encouraging engagement on social media and the Engineering Mindset website for more learning resources.