# Resistor: What, How, and Why

## Resistor: What, How, and Why

Resistor is a passive electrical component that implements electrical resistance as a circuit element. It is one of the most common and essential components in any electronic circuit. In this article, we will learn about what resistor is, how it works, what types of resistor are available, where it is used, and why we need to know about it.

### What is resistor?

A resistor is a device that resists the flow of electric current in a circuit. It converts electrical energy into heat energy, which is dissipated into the surrounding environment. The amount of resistance that a resistor offers depends on its physical properties, such as its material, shape, size, and temperature. The unit of resistance is ohm (Ω), named after the German physicist Georg Ohm.

### How does resistor work?

The basic principle of resistor is based on Ohm’s law, which states that the voltage (V) across a resistor is proportional to the current (I) passing through it, where the constant of proportionality is the resistance ®. The formula of Ohm’s law is:

V = IR

This means that if we apply a certain voltage across a resistor, we can calculate the current that will flow through it by dividing the voltage by the resistance. Conversely, if we measure the current that flows through a resistor, we can calculate the voltage across it by multiplying the current by the resistance.

### What types of resistor are available?

There are many types of resistor available in the market, each with different characteristics and applications. Some of the common types are:

- Fixed resistor: A fixed resistor has a fixed value of resistance that does not change with temperature, time, or voltage. It is usually marked with color bands or numbers that indicate its value and tolerance. Fixed resistors are used to limit current, divide voltage, bias transistors, terminate transmission lines, and other purposes.
- Variable resistor: A variable resistor has a variable value of resistance that can be adjusted by a knob, slider, or screw. It is used to control current, voltage, signal level, brightness, volume, frequency, and other parameters. Some examples of variable resistors are potentiometer, rheostat, trimmer, and thermistor.
- Special resistor: A special resistor has a special function or behavior that differs from normal resistors. It is used for specific applications or situations. Some examples of special resistors are light-dependent resistor (LDR), metal oxide varistor (MOV), negative temperature coefficient (NTC) resistor, positive temperature coefficient (PTC) resistor, and fusible resistor.

### Where is resistor used?

Resistor is used in almost every electronic circuit and device. Some of the common applications are:

- LED circuit: A LED (light-emitting diode) is a semiconductor device that emits light when an electric current passes through it. However, a LED cannot withstand high currents and voltages without being damaged. Therefore, a resistor is used in series with a LED to limit the current and protect the LED from burning out.
- Voltage divider: A voltage divider is a simple circuit that divides an input voltage into two or more output voltages using resistors. It is used to reduce voltage levels, create reference voltages, measure voltages, and other purposes.
- RC filter: A RC filter is a circuit that uses a resistor and a capacitor to filter out unwanted frequencies from an input signal. It can act as a low-pass filter (LPF), which passes low frequencies and blocks high frequencies; or as a high-pass filter (HPF), which passes high frequencies and blocks low frequencies. It is used to remove noise, smooth signals, shape waveforms, and other purposes.

### Why do we need to know about resistor?

Resistor is an important component that affects the performance and functionality of electronic circuits and devices. By knowing about resistor, we can understand how circuits work, how to design circuits properly, how to troubleshoot problems, how to choose the right type and value of resistor for our needs, and how to use resistor safely and efficiently.

### Conclusion

Resistor is a passive electrical component that implements electrical resistance as a circuit element. It resists the flow of electric current in a circuit and converts electrical energy into heat energy. There are many types of resistor available with different characteristics and applications. Resistor is used in almost every electronic circuit and device for various purposes. Knowing about resistor can help us improve our skills and knowledge in electronics.