Ohmic resistors are fundamental components in electrical engineering. They are present in every circuit, so the calculation of resistances is of elemental importance. Here, you will learn all the formulas and also find a practical online tool for easy and quick calculations.
Calculating Electrical Resistance
The relationship between voltage, current, and resistance is crucial for calculating resistance. Electrical resistance is directly proportional to the applied voltage and inversely proportional to the current flowing through the conductor.
Resistance Calculation Formula
The calculation of electrical resistance is done using Ohm’s law:
$$ R = \frac{U}{I} $$
In this formula, $R$ is electrical resistance, $U$ is the applied voltage, and $I$ is the current. The unit of electrical resistance is Ohm (Ω).
If you need to calculate the voltage drop across a resistance, you can rearrange the formula as follows:
$$ U = R \cdot I $$
To calculate the current through a resistance, you can rearrange the formula as follows:
$$ I = \frac{U}{R} $$
Resistance Online Calculator
You can quickly calculate Ohmic resistance with the following online tool. Simply enter two known values from voltage, current, and resistance to calculate the missing value.
Example Calculation
Suppose a voltage of 24 V drops across a resistance, and a current of 0.8 A flows through the resistance. Using Ohm’s law, you can calculate the resistance as follows:
$$ R = \frac{U}{I} = \frac{24V}{0.8A} $$
$$ R = \frac{24V}{0.8A} = 30 \Omega $$
In this example, the Ohmic resistance is 30 Ω.
Further Information
The Ohm Triangle
The Ohm triangle is a helpful tool to better visualize and understand the relationship between voltage (U), current (I), and resistance (R).
Imagine a triangle where each corner represents one of the three quantities. This allows us to derive all the formulas for resistance calculations at any time:
- Voltage Formula: $U = R \cdot I$
- Current Formula: $I = \frac{U}{R}$
- Resistance Formula: $R = \frac{U}{I}$
The Ohm triangle is easy to remember, so you can have the necessary formulas for manual calculations on hand, even without a resistance calculator (for example, during an exam).
Resistance Unit
Electrical resistance is measured in Ohms, represented by the symbol Ω (Omega). Voltage is measured in Volts (V), and current is measured in Amperes (A). The relationship between these units gives the resistance unit:
$$ \Omega = \frac{V}{A} $$
Other Types of Circuits
This article focuses on the calculation of an individual resistance. Often, resistors are also connected in series or parallel.
In a series circuit, resistors are arranged one after the other in the circuit. The current passes through each resistor in succession, and the total voltage is the sum of the individual voltages across each resistor. You can find all the information on calculating a series connection of resistors here.
In a parallel circuit, resistors are arranged in parallel in the circuit. In this circuit, the current flow divides among the different resistors, and the voltage across each individual resistor is equal to the total voltage. You can find all the information on calculating a parallel connection of resistors here.
