# Electronics Basics: Resistance

> An introduction to resistance in electronics: how it limits current, why it is measured in ohms, and how Ohm's law R = V / I ties voltage and current together.

Author: [Flavio Copes](https://flaviocopes.com/about/) | Published: 2020-12-14 | Topics: [Arduino](https://flaviocopes.com/tags/electronics/) | Canonical: https://flaviocopes.com/electronics-resistance/

If you connect the + and - poles of a battery with each other, the amount of current flowing will be too much and would damage the battery. The electrical flow is too much to handle.

We need to introduce the concept of **resistance**, a restriction to electrical flow.

Resistance limits the current flowing in a circuit. Every component in a circuit has _some_ resistance. Even the wire has some resistance, but it's very very low.

Resistance is measured in **ohms** (`Ω`).

1 ohm is defined as 1 volt divided by 1 ampere:

<p class="inline">
<code>1 Ω = 1 V / 1 A</code>
</p>

<br><br>

This is what we call **Ohm's law**: `R = V / I`, where R is the symbol for resistance, V is the symbol for voltage and I is the symbol for current.

From this we can derive that:

- `V = R * I`
- `I = V / R`

A **resistor** is a component that's created exclusively to provide a certain amount of resistance.

We have resistors of various values. Common ones you will find used in circuits are `220Ω`, `1kΩ`, `4.7kΩ`, `10kΩ`, and so on.

Given Omh's law, we can calculate the current flowing in a circuit when you know the voltage provided by the battery, and the resistance that's provided by the circuit components.

If the battery provides `5V` and the circuit provides a `1kΩ` resistance, The current flowing will be `5mA`.