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Voltage divider rule

Voltage divides in series circuit only. In parallel circuit voltage remains same. All of the loads are connected parallelly across voltage source so that loads have two common points with source positive and negative terminals.

same voltage in parallel connection

Considering above circuit three resistors are connected parallelly with source of 220V. Question is what the drop voltage is across three resistors 10, 20 and 30 ohms? The answer is 220V of course. Because three resistor’s positive terminals are connected with the source positive terminal and negative terminals are connected with source negative terminal so voltage remains same at parallel circuit.

In our household the total circuit is connected parallelly so all the electronic devices get same voltage and they can use their full power. If we connect some same power bulbs in series, one bulb will give shining light, second bulb will give less light and third one will less more light because here voltage divides. TV, fridge, bulb, fan etc all are connected in parallel and they take current according to their requirement. Series connection means voltage division and parallel connection means current division.


rule of voltage division


If we connect the same resistors in series then voltage will not same it will divide according to resistor value. We know current flows positive terminal to negative terminal. It is the concept of electrical engineering. Science concept is current flows from negative to positive terminal. Actually positive charge has more mass than electron so it does not move; electron moves and comes to positive charge to neutral it. So we can say 30ohm resistance has more voltage than other two resistors, then 20ohms voltage and 10ohm resistor gets less voltage than other two resistors.

Voltage divider formula


voltage divider formula


Voltage divider rule is that rule if a series circuit has more than one resistor; the voltage across of each resistor is the ratio of resistor value multiplied with voltage source to total resistance value.

Let us consider above circuit there is three resistances. We have to find out each resistance voltage. Using voltage divider rule,


potential divider rule

It is also know as voltage formula.

Example of voltage divider rule: Example of Voltage divider rule

For example of voltage divider rule now we will solve the simple circuit has 6V source and 200 ohm, 100 ohm resistance. We will find voltage drop across each resistance.

Applying formula,

Voltage across 100Ω resistance V1 = (100*6)/(200+100) = 2V

Voltage across 200Ω resistance V2 = (200*6)/(200+100) = 4V


Current divider rule

Series circuit same current, parallel circuit current division. Current remains same in series circuit. It only divides in parallel circuit.


same current at series connection


Considering above circuit there are three resistance R1 , R2 , R3 connected in series having same current I. They are experiencing same current although voltage is different.

We know current is flow of charge per unit time through conductor. Equation of current is I = Q/t .

Let us consider the conductor of this circuit carries 100 C charges per second. Here first resistance prevents flow of charge rate then second resistance gets less charge than first one and third one gets more less than first two resistances. If we remove first resistance, second resistance will get same flow rate which first one experienced, if we remove first and second resistance third one will experience same flow of charge which first one observed. In a word we can say flow of charge remains constant either any of resistance is added or removed. So flow of current remains same for series circuit. Current divides parallelly.


current divider formula


We see here in figure I current are coming and divided into I1 and I2 via two resistance.

The formula of current divider rule is


formula of current divider


The current of each resistor is the ratio of multiplication of total current and opposite resistor value with total resistance.

In our household current divider rule is applied. We use different types of electronic devices. Some of them need small current some of them need huge current. When they are connected in parallel there is no clash between them. No one effects others power taking system. They take current as required. If they are in series then they will not independent. As parallel connection all are independent and takes current as need. Current divider rule is only applicable for two resistors when many resistors are connected in parallel some other methods will be applied to find each current value.

Example of current divider rule:


example of current divider


A circuit caring I current and divides across two resistors viz. 10Ω and 15Ω .

According to current divider rule,

Current for 10Ω resistance, I1 = (15*I)/(10+15) = 15I/25 = 0.6I

Current for 15Ω resistance, I2 = (10*I)/(10+15) = 10I/25 = 0.4I

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Md Ebrahim Shah

Electrical Engineer, teacher, professional article writer and founder of His passion is to describe electrical technology at easy way as people can get clear conception and upgrade the technology for the better human life.

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