### 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.

### Application

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.

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 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**

so

**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.