Electronics Basics

Ohm’s Law

Ohm’s Law deals with the relationship between voltage and current in an ideal conductor. This relationship states that: The potential difference (voltage) across an ideal conductor is proportional to the current through it. The constant of proportionality is called the “resistance”, R.

I (Current) = V (voltage) / R (resistance)

For Example, if we are given voltage through a Component and resistor of that component, we can find Current through it.


We can calculate amount of current flowing through resistor, likewise in this case.

Applying Ohm’s Law:

I = V / R

On, Putting Values:

I = 9 / 9 = 1 Ampere

Hence we get value of Current 1 Ampere

Selecting Resistance

When you will be building circuit to Blink an Led using Arduino, or Glowing Led you will need this concept.

In this image you can see voltage below resistance is given to be 3 V. We can calculate value of resistance. As I=V/R:

I = 3 / 20

As max current req by Led is 20 mA.

I = 0.15 * 1000

As current is in milliAmps.

Kirchhoff’s Voltage Law

Do you wonder How were those values 2 V and 3 V were written. That was possible with the help of Kirchhoff’s Voltage Law. What does that state?

It states that the total voltage around a closed loop must be zero.

How to apply Kirchhoff’s Voltage Law.

There is a sign convention (if we go from lower potential to higher potential then it takes + ve sign).

Now again coming back to question that how do i get that 2 V and 3 V potential values.

First of all that 2 V is the value required by LED (LED can get max of 2 V across it), we get that 3 V by applying Kirchhoff’s Voltage Law:

5 – I * R (voltage across resistance) – 2 = 0


I * R = 3

As the current required by LED is 20 mA.

After Putting Value of Current we get value of resistance as 250 Ω.

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Sergei Ermilov

I create web projects, come up with ideas, develop, optimize and promote websites. The first steps in this direction were taken in 2008. If you have any ideas or want to suggest something, then write to me and my team.

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