What is a Resistor, Why is it used and How does it work?

What is a Resistor?

A Resistor is a two-terminal electronic component which provides resistance to the flow of current. You can think of current as electrons flowing between two terminals of any power source, and resistance as some kind of obstruction to the flow of current.

By placing a resistor between the flow of current, the amount of current that flows between its two terminals can be reduced (controlled). You may visualise resistor as a speed breaker to the flow of current.

One common analogy can be made by considering current as flow of water through a pipe and resistor as some kind of fixed valve/constriction fitted in between the pipe. If the constriction is very narrow, the flow of water reduces and vice versa. Similarly if the resistance of a resistor is high, the flow of current reduces and vice versa.

Barring Superconductors, every other material has some resistance and can be used as a resistor. If the resistance any material is very less, it is categorised as a conductor. Otherwise it is categorised as an insulator.

Why is a Resistor Used?

A question that might pop up in your mind is: why do we need to reduce the current flow? Isn’t it counter intuitive to waste the potential of flowing current by using a resistor?

Well, there are many reasons for doing it. One simple example is what we do while powering an LED. LED’s are very sensitive to the amount of current flowing through. If more current flows through the LED, it burns out and stops working. A resistor can help us here to reduce the current that flows through the LED.

Apart from the above use case i.e., they can be used to reduce current flow, they can also be used to achieve the following use cases:

  • Adjust signal levels / Divide voltages: If there is some data coming from a sensor at a higher voltage and we need to pass it to a micro-controller operating at a smaller voltage, a resistor can be used to reduce the signal level from the sensor.
  • Generate heat: Resistors reduce the flow of current by emitting some of the energy in the form of heat. Hence can be used in places where reliable and controllable source of heat is required.
  • Pull-Up & Pull-Down voltages: In digital circuits even tiny electrostatic charges can trigger a response, which is not expected. Resistors can help prevent false triggers by pulling up/down voltage at any point in the circuit.

How does a Resistor Work?

Any material (except superconductors) will resist the flow of current. If it is a conductor, the resistance to the flow of current is less and vice versa for an insulator. A Resistor works by using this natural property of resistivity/conductivity of any material. It absorbs energy from the flow of electrons (electric energy) and dissipates in the form of heat (thermal energy).

[TODO] An article on different types resistors and how they are constructed will be added soon.