Resistor

What is a resistor?

A resistor is a small component used in electrical circuits to limit or control the flow of electric current. It doesn't store energy, it just resists current.

Unit of measurement Ohms (Ω)

Resistance is measured in ohms, written with the symbol Ω.

Sometimes you'll see:
- kΩ for kilo-ohms = 1,000 ohms.
MΩ for mega-ohms = 1,000,000 ohms.

Why use a resistor?

- To protect components like LEDs from too much current. It'll slow down the flow of current so only a safe amount reaches the LED.
- To control how much current flows through a part of a circuit, because different parts may need different amounts of current.
- To divide voltage in a circuit. If you connect two resistors in series and measure the voltage between them, you'll get a fraction of the total supply voltage.
- To set timing in circuits. Resistors are often used with capacitors to create delays or timing functions (how long something stays on or how fast it blinks).

How a resistor works

Resistors work by resisting the flow of current. How much they resist depends on their resistance value (in ohms).

This relationship is described as Ohm's Law:

Where:
- I = Current in amperes (A)
- V = Voltage in volts (V)
- R = Resistance in ohms (Ω).

What this means:
- If voltage stays the same, and you increase resistance, the current goes down.
- If you decrease resistance, more current flows.
- If you know any two values (voltage, current or resistance, you can calculate the third).

Example:

Let's say you have a 5V power supply and connect it to a 1,000 Ω (1kΩ) resistor:

This means 5 milliamps of current will flow through the resistor.

If you use a 2,000 Ω resistor instead:

That's less current, because the resistance is higher.

I made this lil calculator to save you working it out yourself: