3.4 - Combining Resistances in Series and Parallel
Enroll to start learning
You’ve not yet enrolled in this course. Please enroll for free to listen to audio lessons, classroom podcasts and take practice test.
Interactive Audio Lesson
Listen to a student-teacher conversation explaining the topic in a relatable way.
Resistance in Series
🔒 Unlock Audio Lesson
Sign up and enroll to listen to this audio lesson
Today, we will explore how resistances combine in series. Can anyone tell me what happens to the total resistance when we connect resistors in series?
The total resistance increases because you just add them up!
That's correct! The total resistance R_total is simply the sum of the individual resistances: R_total = R_1 + R_2 + R_3. For example, if R_1 is 2Ω, R_2 is 3Ω, and R_3 is 5Ω, what is R_total?
It would be 10Ω.
Exactly! And remember, the current remains the same through all resistors. Can anyone explain why that is important?
It's important because if one resistor fails, the entire circuit stops working.
Right! This series configuration is crucial for applications like string lights. Let’s summarize: in series, we increase resistance, keep current constant, and it’s useful for high voltage applications.
Resistance in Parallel
🔒 Unlock Audio Lesson
Sign up and enroll to listen to this audio lesson
Now that we understand series combinations, let’s delve into parallel combinations. In a parallel circuit, how do we calculate total resistance?
We take the reciprocal of the sum of the reciprocals of the individual resistances.
Spot on! The formula is: 1/R_total = 1/R_1 + 1/R_2 + 1/R_3. Can anyone provide an example?
If we have resistors of 2Ω, 3Ω, and 6Ω in parallel, then it would be 1/R_total = 1/2 + 1/3 + 1/6.
Correct! When calculated, we find R_total is 1Ω. What happens to the voltage and current in a parallel circuit?
The voltage across all resistors remains the same, and the total current is the sum of the currents in each branch.
Exactly! This is why parallel configurations are so common in household wiring. Let’s summarize: in parallel connections, voltage is constant, current increases, and it’s useful for high current applications.
Introduction & Overview
Read summaries of the section's main ideas at different levels of detail.
Quick Overview
Standard
The section explains the principles behind combining resistances in series and parallel, including formulas for calculating total resistance. It covers important characteristics unique to each configuration, such as current and voltage behavior, and provides examples for practical understanding.
Detailed
Combining Resistances in Series and Parallel
This section explains the methods to combine resistances in electrical circuits, focusing on two predominant configurations: series and parallel. When resistors are connected in series, the total resistance is calculated as the sum of the individual resistances, expressed by the formula:
$$R_{\text{total}} = R_1 + R_2 + R_3 + \ldots$$
In this configuration, the current flowing through each resistor is constant, while the voltage drop varies across each resistor according to Ohm's Law. An example provided illustrates this: if resistors of 2Ω, 3Ω, and 5Ω are connected in series, the total resistance becomes 10Ω.
Conversely, when resistors are connected in parallel, the total resistance is calculated using the reciprocal of the sum of the reciprocals of the individual resistors:
$$\frac{1}{R_{\text{total}}} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} + \ldots$$
In parallel connections, the voltage across each resistor remains consistent, while the total current is the cumulative current through each branch. An example shows that if resistors of 2Ω, 3Ω, and 6Ω are in parallel, the total resistance is 1Ω.
This section highlights that understanding how to manipulate resistor configurations is vital for circuit design and analysis, affecting overall circuit performance such as voltage supply and current flow.
Youtube Videos
Audio Book
Dive deep into the subject with an immersive audiobook experience.
Resistance in Series
Chapter 1 of 3
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
When resistances are connected in series, the total resistance \( R_{\text{total}} \) is the sum of the individual resistances:
\[ R_{\text{total}} = R_1 + R_2 + R_3 + \ldots \]
In a series circuit, the current remains the same across all resistors, but the voltage across each resistor varies depending on its resistance.
Detailed Explanation
When resistors are arranged in a series configuration, they are connected end to end, forming a single path for current to flow. The total resistance of the circuit increases because the current must pass through each resistor consecutively. This means that the total resistance is calculated by simply adding the resistance values of each resistor. Importantly, while the total resistance increases, the current flowing through the circuit remains consistent throughout all resistors as per Ohm's Law.
Examples & Analogies
Imagine a line of people passing a ball down the line. Each person represents a resistor, and the ball represents the electric current. The more people in line, the longer it takes for the ball to reach the end, similar to how total resistance increases with more resistors in series. However, each person can only pass the ball after receiving it - this is akin to maintaining the same current flowing through each resistor.
Resistance in Parallel
Chapter 2 of 3
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
When resistances are connected in parallel, the total resistance \( R_{\text{total}} \) is given by the reciprocal of the sum of the reciprocals of the individual resistances:
\[ \frac{1}{R_{\text{total}}} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} + \ldots \]
In a parallel circuit, the voltage across all resistors is the same, but the current is divided among the resistors depending on their individual resistances.
Detailed Explanation
In a parallel arrangement, all the resistors are connected across the same two points, providing multiple pathways for the current to flow. The key point here is that the voltage across all resistors in parallel remains the same. However, the total resistance decreases because the current has multiple routes. To find the total resistance in this case, we calculate the reciprocal of the sum of the individual resistances’ reciprocals. This effectively creates a scenario where adding more parallel resistors reduces the total resistance of the circuit, allowing more current to flow overall.
Examples & Analogies
Think of water flowing through several parallel pipes leading to the same destination. If one pipe is narrow (high resistance), water can still flow through the other wider pipes (lower resistance). Adding more pipes reduces the overall resistance to flow, allowing more water (current) to reach the destination quickly, similar to how adding resistors in parallel lowers total resistance and increases current capacity.
Example of Series and Parallel Combinations
Chapter 3 of 3
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
Series Combination:
If \( R_1 = 2 \Omega \), \( R_2 = 3 \Omega \), and \( R_3 = 5 \Omega \) are connected in series, the total resistance will be:
\[ R_{\text{total}} = 2 \Omega + 3 \Omega + 5 \Omega = 10 \Omega \]
Parallel Combination:
If \( R_1 = 2 \Omega \), \( R_2 = 3 \Omega \), and \( R_3 = 6 \Omega \) are connected in parallel, the total resistance will be:
\[ \frac{1}{R_{\text{total}}} = \frac{1}{2 \Omega} + \frac{1}{3 \Omega} + \frac{1}{6 \Omega} = 1 \Omega \]
Detailed Explanation
In the series combination example, we simply add the resistances together: 2 Ω + 3 Ω + 5 Ω equals a total of 10 Ω. This demonstrates the principle that series resistors increase the total resistance. In the parallel combination example, we need to use the reciprocal sum formula. By calculating the reciprocal of each resistance value, we find the total resistance must be calculated to provide the overall impedance to current flow, which results in a lower resistance of 1 Ω. This emphasizes that in parallel arrangements, the overall resistance decreases.
Examples & Analogies
Imagine when you’re in a room with three closed doors (series). You have to go through each one to exit. If each door has some weight making it harder to push (resistance), then you feel the total weight of three doors. In contrast, if each door leads to different exit points (parallel), you can choose one that’s easiest to push open. The overall effort it takes to get out is reduced.
Key Concepts
-
Total Resistance in Series: Total resistance is the sum of individual resistances.
-
Total Resistance in Parallel: Total resistance is calculated using the reciprocals of individual resistances.
-
Voltage and Current Behavior: Series connections have constant current, while parallel connections share the same voltage.
Examples & Applications
For three resistors of 2Ω, 3Ω, and 5Ω in series, the total resistance is 10Ω.
For three resistors of 2Ω, 3Ω, and 6Ω in parallel, the total resistance is 1Ω.
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
In series they stack, the total is clear, / Resistance sums up, there's no need for fear.
Stories
Imagine a train where each car is a resistor; they must all line up in a row to go forward, just like resistors do in series.
Memory Tools
For series think 'S' for 'Sum', for parallel think 'P' for 'Parts' where current splits.
Acronyms
SP
Series adds
Parallel divides. S for Sum
for Parts.
Flash Cards
Glossary
- Resistance
The opposition to the flow of electric current in a conductor, measured in Ohms (Ω).
- Series Connection
A configuration of resistors where the current flows through each resistor sequentially, summing their resistances.
- Parallel Connection
A configuration of resistors where the current can split across multiple paths, allowing for individual voltage across each resistor.
Reference links
Supplementary resources to enhance your learning experience.