How to use Ohm's Law: Instructions for beginners with examples

I do not usually use a lot of math, when engaged in electronics. But Ohm's law - a rare exception :)

The law was put Georg Ohm, and is based on the relationship of voltage, current and resistance:

Fig. 1. Illustration connection resistance (Ohm), the current (Amp) and voltage (Volt)

Look at the picture above and see whether it makes sense for you:

If you increase the voltage in the circuit, with constant resistance, you get more current.
If you increase the resistance in the circuit, while the voltage remains the same, you get less current.

Ohm's law - a way to describe the relationship between the voltage, current and resistance with the use of mathematics: V = R * I, where

V - voltage;
I - current;
R - is the symbol of resistance.

You receive and modify the formula R = V / I or I = V / R. As long as you have two variables, you can calculate the latest.

Ohm's Law triangle

You can use this triangle to remember Ohm's law:

How to use it:

Use your hand to cover the variable that you want to find. If the remaining letters are arranged one above the other, which means to divide the top from the bottom. If they are next to each other, which means to multiply one by the other.

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Example: you have to find the voltage

Closing V in the triangle, then we look at R and I. I R and next to one another (on the same horizontal line), so you need them to multiply. This means that you will get:

V = I * R

It's simple!

Example: We need to find resistance

Put your hand on R. Then you will see that V over I. This means that you have to share on the V I:

R = V / I

Example: you have to find the amperage

Place your hand over I. Then you will see V over R, which means the division of V with R:

I = V / R

Practical examples of the use of Ohm's law

EXAMPLE 1

The best way to learn to use it by example.

Below is a very simple circuit with a battery and a resistor. The battery is a voltage source of 12 volts and resistor 600 ohms. How much current flows through the circuit?

To find the current value, you can use the triangle to the above formula for the current: I = V / R. Now you can calculate the current by using the voltage and resistance:

I = 12 V / 600 ohm
I = 0,02 A = 20 mA (milliamps)

Thus, the current in the circuit is 20 mA.

EXAMPLE 2

Let's try another example.

Below we have a circuit with a resistor and battery again. But this time, we do not know the battery voltage. Instead, we imagine that we have measured the current in the circuit and found that it is 3 mA (milliamps).