# Find the Equivalent Resistance Between A and B

When it comes to analyzing electrical circuits, one common task is to determine the equivalent resistance between two points. This is particularly useful in situations where multiple resistors are connected in various configurations, such as series or parallel. By finding the equivalent resistance, we can simplify the circuit and make further calculations or analysis easier. In this article, we will explore different methods and techniques to find the equivalent resistance between points A and B, providing valuable insights and examples along the way.

## Understanding Resistance

Before diving into finding the equivalent resistance, let’s first understand what resistance is. Resistance is a fundamental property of any material that opposes the flow of electric current. It is measured in ohms (Ω) and denoted by the symbol R. The higher the resistance, the more difficult it is for current to flow through a material.

Resistance can be influenced by various factors, including the length and cross-sectional area of a conductor, as well as the material’s resistivity. Different materials have different resistivities, which determine their inherent resistance. For example, copper has a lower resistivity compared to steel, making it a better conductor of electricity.

## Series and Parallel Resistors

When resistors are connected in a circuit, they can be arranged in two common configurations: series and parallel.

### Series Resistors

In a series configuration, resistors are connected end-to-end, forming a single path for current to flow through. The total resistance in a series circuit is the sum of the individual resistances. Mathematically, we can express this as:

Req = R1 + R2 + R3 + … + Rn

For example, let’s consider a series circuit with three resistors: R1 = 10Ω, R2 = 20Ω, and R3 = 30Ω. The equivalent resistance can be calculated as:

Req = 10Ω + 20Ω + 30Ω = 60Ω

### Parallel Resistors

In a parallel configuration, resistors are connected side by side, providing multiple paths for current to flow through. The total resistance in a parallel circuit can be calculated using the following formula:

1/Req = 1/R1 + 1/R2 + 1/R3 + … + 1/Rn

Let’s consider a parallel circuit with three resistors: R1 = 10Ω, R2 = 20Ω, and R3 = 30Ω. The equivalent resistance can be calculated as:

1/Req = 1/10Ω + 1/20Ω + 1/30Ω

1/Req = 3/30Ω + 2/30Ω + 1/30Ω

1/Req = 6/30Ω

1/Req = 1/5Ω

Req = 5Ω

## Combining Series and Parallel Resistors

In real-world circuits, it is common to have a combination of series and parallel resistors. To find the equivalent resistance in such cases, we need to apply a step-by-step approach.

### Step 1: Simplify Series and Parallel Sections

The first step is to identify any series or parallel sections within the circuit and simplify them. By doing so, we can reduce the complexity of the circuit and make it easier to find the equivalent resistance.

Let’s consider a circuit with two resistors, R1 = 10Ω and R2 = 20Ω, connected in parallel. This parallel combination is then connected in series with another resistor, R3 = 30Ω. To find the equivalent resistance, we can simplify the parallel section first:

1/Req1 = 1/R1 + 1/R2

1/Req1 = 1/10Ω + 1/20Ω

1/Req1 = 3/30Ω + 2/30Ω

1/Req1 = 5/30Ω

1/Req1 = 1/6Ω

Req1 = 6Ω

Now, we have simplified the parallel section and found the equivalent resistance as 6Ω. We can represent this simplified section as a single resistor with a resistance of 6Ω.

The circuit now becomes a series combination of Req1 = 6Ω and R3 = 30Ω. To find the equivalent resistance of this series combination, we can simply add the resistances:

Req = Req1 + R3

Req = 6Ω + 30Ω

Req = 36Ω

Therefore, the equivalent resistance between points A and B in this circuit is 36Ω.

## Q&A

### Q1: Can the equivalent resistance ever be lower than the smallest resistor in a circuit?

A1: No, the equivalent resistance can never be lower than the smallest resistor in a circuit. The equivalent resistance is always greater than or equal to the smallest resistor. This is because resistors in parallel provide additional paths for current to flow, reducing the overall resistance. However, adding more paths will never decrease the resistance below the value of the smallest resistor.

### Q2: What happens if all resistors in a parallel configuration have the same resistance?

A2: If all resistors