Ohm’s Law – Ohm’s Law is a law that states the ratio between voltage, current and resistance. Ohm’s law is say:

“**The amount of electric current is directly proportional to the voltage and inversely proportional to the resistance**“

That is, the current passing through the circuit will be large if the given voltage is large and the resistance in the circuit is small. Conversely, the current passing through a circuit will be small, if the electrical voltage is small and resistance is large.

This ohm law is also expressed by the triangle formula. Look at the following picture below:

To get the voltage value (V), the formula is:

**V = I x R** or **V (voltage) = I (current) multiplied by R (resistance)**

To get the current value (I), the formula is:

**I = V / R** or **I (current) = V (voltage) divided by R (resistance)**

To get a resistance value, the formula is:

**R = V / I** or **R (resistance) = V (voltage) divided by I (current)**

The formula above is the most basic formula for understanding an electric state. Almost all electronic circuits use this formula. For example, the basic use of calculations using this formula is to calculate a resistance used to turn on an LED light. Look at the following picture below:

in the picture above, figure (a) is a schematic and (b) is an example of a real objectc. We cannot connect the LED directly to the 9V battery because it can cause the LED to burn. The LED has a drop voltage, which is the working voltage for turning on the LED.

Generally this LED working at voltage or drop voltage is 2 Volt and the current needed is 20mA. If a voltage of 9V is given, the current that flows will be large which can cause the semiconductor filament LED to burn. To overcome this, a resistor is used which will resist the flow of electricity current. Because we want to find the resistance value, we will use the formula:

**R = V / I** or **R (resistance) = V (voltage) divided by I (current)**

= (Vsource – Vdrop) / I

= (9V – 2V) / 20mA

= 7V / 20mA

= 7V / 0.02A = 350 Ohm

So, a good resistance to use on these LEDs is a resistor with a 350 Ohm resistance value. But in the market I have never found this resistance value, so it can be replaced with a 330 Ohm resistance value. Note in figure (a), the resistor consists of several colored bracelets. If you want to learn about this color code, please read the Resistor Color Code Resistance Value.