# What is Resistor and How does it work?

### What is Resistor and How does it work?

Easy question, Hard answer! usually when you ask somebody what is resistor, they’ll tell you ” Resistor is an electrical component that resist against flow of electric charge (Current)”.  It’s correct answer but today I want to explain you what is a resistor in a different way.

let’s try hydraulic analogy! easy way to explain electronic fundamentals.

Imagine in below simple circuit as you can see, replace Electrons with Water, Copper wires with Pipes, Power supply with Pump &  Resistor with a Thin pipe or Sand filter or Valve. In below system water pressure represent Voltage (V).

In this hydraulic ( water ) system, when we replace a thin pipe with a thinner one, water flow will be decreased and then water pressure will be decreased more than previous state. if this is unclear don’t worry, in next lines I’ll explain more and in easier way.

Easy to realize model

Lets try with below image. in below system we have a pump as power supply, sand filter as resistor, you know pipes are here as wires and water as electrons.

What is sand filter?! sand filter is a piece of pipe filled by sand so that sands can’t move but water can pass trough the sands. volume of passed water depends on the sands sizes, we can use course and fine sands to make sand filter. when we use course sands ( bigger sizes ) since empty space between sands increases, water can flow easier then we have low resistance and if we use fine sands ( smaller sizes ) since empty space become less, water flow will be more difficult and we have high resistance in system. Ok?

Electronic resistor is like sand filter and in electronic circuits we use this component to limit current. When we use  high resistance charge flow become more difficult for the electrons.

You may ask “How much water can pass trough a sand filter?” I should say, it depends on the pressure the pump can generate. I’m sure you saw this many times in daily life, some times we open water valve to fill a bottle, if water pressure was low it takes a long time to fill other wise it takes a short time.

In Electronic Circuits we are facing a similar behavior. Imagine you have an Edison light bulb, you saw when we connect this light bulb to 110v/220v it can make light for us but when we connect it to a 1.5v battery it doesn’t have any light, it means very little amount of current pass trough the lamp.

I know you are thinking to Edison lamp now! You may ask ” Why Edison lamp shines and gets warm? ” I answer to this question below.

In above hydraulic system Imagine water pressure increases more and more, now when water pass the filter, friction between water and sand cause water and filter become warm. In Edison lamp we have same behavior. when electrons pass the resistor make heat. In Edison lamp, since electron flow, filament get very hot and shine. all of resistors make heat. the amount of produced heat depends on Current and Voltage of resistor ( P=VI ). all of resistors have specified wattage and the wattage number ( 1/8, 1/4, 1/2, 1, 2, 5, 10, 100, … ) represent maximum power the resistor can dissipate.

Ohm law: Ohm law is very important rule we can use to calculate Current, Resistor & voltage of linear components. save ohm law in your memory, it is very important. Ohm law said : V=R*I ! it’s very simple, also we can write this equation in these forms: I=V/R & R=V/I.

Now you know what is resistor and how it works.

How do resistors in parallel or series work?

Are you interested in sand filters? I want to check sand filters behavior in series and parallel. let’s start with series.

Imagine you have two same sand filter, if you put sand filters in series like below image.

as you see above, We can replace these two filter with a new filter equal to two of previous ones in height and made by same sand sizes ( What I said ? 😀 ).I mean height of new filter = height filter 1 + height filter 2. in electronic circuits when we have two series resistance,  Resistance of equal resistor= Resistor 1 Resistance + Resistor 2 resistance.

Now let’s try parallel resistor. if you have hydraulic system like below image then water pressure on two resistors is same, then water flow  increases compared with previous state we don’t have any parallel resistor. Total flow= flow 1 + flow 2 then if we want use an equal filter with same type sand , our equal filter height will be less than height of each filters. if 2 parallel filter have same height then height of new filter equal to 1/2 of one of filters height.

In Circuit boards if we have 2 equal resistors in parallel, total resistance of them equal to 1/2 resistance of one of them.

General formula for non equal resistors in parallel:

Req = ( R1 * R2 ) / ( R1 + R2 )