Electricity Tutorial - Voltage, Current & Resistance

Ohm’s Law:

Voltage, Current and Resistance are three commonly used terminologies in electronics. Georg Ohm was the person who defined a relationship and determined that current flowing through a conductor is directly proportional to its cross sectional area and inversely proportional to the length of the conductor. This law is quite confusing on the first stance. Let us understand an analogy to current, voltage and resistance and redefine Ohm’s law it in a better way.

The best and widely used example is the water analogy (also known as hydraulic analogy). Assume that you have a Pump to push water from your tank to your garden, connected by a pipe. When you switch on, water rushes through the pipe and reach your plants. However, you need to control the flow of water to avoid damage to the plants. So, you set up a throttle (or a pressure regulator) to control the flow of water. If you increase the throttle, water rushes out rapidly with greater pressure. If you reduce and manage it, you can control the flow of water. This analogy may not be exact, but will help you understand the basic concepts.

Now let us understand the terminologies and their relation, beginning with Voltage.


As per our water analogy, Pump pushes water through the pipe with certain amount of force. This causes a pressure difference between two ends of the pipe and water is pushed towards the other end. Similarly for the electrons to move, the battery generates certain amount of force to push the electrons from one point to another. The pressure difference between these two points is called as potential difference, and the amount of energy required to move the electrons is known as Voltage (V), which measured in Volts


Current (I) is nothing but flow of electrons through a conductor in a particular direction. It has both magnitude and direction. In our water model, it is the amount of water flowing through the pipe. Most metals (conductors) have free electrons wandering within them and when they are positioned between any two charged objects, negatively charged object pushes these free electrons and the positively charged object pulls it, which results in electron movement. Since electrons carry certain amount of charge with them, the result is a flow of charge between the two objects and this flow of charge is known as electricity.
Amount of charge passing through a point at a given time is measured in Coulomb (C) / Second (S), which is called Ampere, or Amp (A).

i.e. 1 Ampere = 1 Coulomb / 1 Second, or 1(C) = 1(A) * 1(S)


The objective of electrons is to move from one end to another end of the conductor generating electricity. However, on the way they hit the atoms and lose their movement. This results in heating the conductor and also the amount of current flowing through the conductor slows down. Every conductor possesses this characteristic to resist the flow of electrons, and this property is known as resistance. Resistance(R) is measured in Ohm (O or Ω). The pipe used in our water analogy exhibits some amount of resistance to the flow of water. If we need to use a throttle in our circuits, then we use a special electronic component called resistor which does the job of resisting the flow of current.


So, why did we do all this? Push the electrons; make them wrestle with the atoms, create electric charge, etc. This is all done to make our life easy; to light a bulb; to run a motor; to heat water in the geyser, so on and so forth. We are converting energy generated from moving electrons to other forms of energy. The rate of conversion of electric energy to other forms of energy is known as Power (P), which is measured in Watt (W).

Now let us redefine Ohm’s law in simple terms. Ohm’s law can be simplified as: “Current through a conductor is directly proportional to the Voltage across its end points and inversely proportional to the Resistance between them”.

For the technically inclined, this can be written in an equation form as:

Where V = Voltage, I = Current, and R = Resistance.

Power is given by the product of Voltage and Current, which is equated as:

Where P = Power, V = Voltage, and I = Current.

This concludes our tutorial on Voltage, Current, Resistance and Power.

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