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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 the amount of current flowing through the 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 a 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 the value of resistance.


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 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 a maximum 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 the value of current we get the value of resistance as 250 Ω.