Ohm’s Law-Voltage, Current and Resistance

Ohm’s Law-Voltage, Current and Resistance

It is important to understand the basics of voltage, current and resistance when starting as a beginner in the world of electricity and electronics. Knowledge and understanding of Voltage, current and resistance are very essential in understanding and utilizing of electricity. These concepts is very easy to understand, though it cannot be seen with the naked eye. It can only be visualize by the use of measurement tools like millimeters, oscilloscopes and spectrum analyzers.

Ohm's Law

Ohm’s Law Better Explained


In this post ,you will learn:

  • What voltage ,current and resistance are
  • How it relates to electrical charge.
  • What Ohm’s law is 
  • Applications of ohm’s law

Electricity is the flow of electrons, without the flow of electric electrons there wouldn’t be power


Voltage is the difference in charge between two points. It can also be defined as  the quantity potential energy between two points in a circuit. Voltage is measured in volts,named after Alessandro Volta the Italian physicist who discovered that chemical reactions can produce electricity.


Current is the rate at which charge is flowing. The unit of current is ampere or amps It is named after Andre Marie Ampere, a French physicist (1775-1836). One ampere of current is defined as the current that flows with electric charge of one Coulomb per second I.e I=q/t where I is current, q is quantity of electric charge measured in coulomb and t is time measured in seconds.


Resistance is the opposition to the flow of electric current). The unit of resistance is Ohm, named after a German physicist called  Georg Simon Ohm. The unit is usually represented with the Greek letter “Ω” which is called omega and pronounced “ohm”.

Ohm’s law

George Simon Ohm (1787-1854) Bavarian scientist who studied electricity. He was the first to show the relationship between current, resistance, and voltage. As a result he devised a law which shows the inter-relationship between the three basic electrical elements (resistance, voltage and current) in 1827.

Ohm’s law states that the amount of electric current flowing through a metallic conductor in a circuit is directly proportional to the applied voltage and inversely proportional to the resistance of the conductor at constant temperature. Mathematically, ohm’s law can be expressed as I=V/R where I is the current flowing through the conductor, V is the potential difference applied (voltage) and R is the resistance of the conductor.

Why is ohm’s law so very important?

Ohm’s Law is the a bedrock of electronics and electricity. Without an intensive  understanding of “Ohm’s law” you will not go very far either in design or in troubleshooting of electronic or electrical circuits. Ohm’s law is used to find out the desired amount of resistance, voltage or current levels to ensure that electronic or electrical  circuits are well designed and in proper choosing of parts. It  is commonly used to know the appropriate resistor value within a circuit in a case where voltage or emf value is known. For example if you want to power a led with a specific voltage, let’s say 9V. Leds usually have a maximum current rating which is often listed on the packaging or datasheets. This is often around 20 to 30 mA. What this means is that you have to limit the current value  coming from the voltage source ,so that it wouldn’t exceed 30mA. Now, this is how we use ohm’s law to get the value of the required resistor.

  • Write out the voltage value which is 9V
  • Write out maximum current value which is 30mA(0.3A)
  • Now, from Ohm’s law formulae which is  V=I*R; input the known values
  • We have R=9/0.3; so R= 30 Ω which is the required resistor for the led.

Practically, it safer to use the average maximum value of the led to be sure you don’t burn out the led.

Let’s take another example, calculate the current and resistance of an electric kettle rate 1000w,240V.

  • Two values were given; 1000w and 240V which are the power and voltage.
  • Take note the formula for power is P=I*V
  • In order to get I (current) Insert the given values, we get I=1000/240; therefore the current is 4.17A.
  • Since current is now known, to the value of the resistance is now made easy.
  • We use the formula V=I*R; R=240/4.17. The value of the resistance is 57.55Ω.

That was easy, isn’t it.

That’s all you need for ohm’s law – remember just two formulas:

  • for voltage V=I * R and;
  • for power P = I*V



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