## Ohms Law

##### The most important principle you need to know in electronics is a principle called ohms(Ω) law. Ohms law is a calculation you can do to calculate the three important terms that there is in Electronics, namely:

##### Voltage

##### Current

##### Resistance

##### Ohm is also the symbol to represent a resistance 🙂

##### The formula is known as V = I * R. So a voltage of the circuit is equal to current times the resistance.

##### In most cases we will always have a voltage like a battery or a power supply, at the beginning you will find yourself either working out the current of the system, or the resistor needed to give a specific calculated current.

## Example

##### So lets go through an example knowing the famous law V = I * R. If you look at the circuit below you will see a basic LED circuit. LED normally runs at max about 20mA. So if we have a 5V battery, what resistor should we chose to make sure the LED does not blow up.

##### If we take Ohms Law. V=I*R and change the subject of the formula. We can get R = V divided by I.

##### This means that the resistance we need to make sure the LED does not go armageddon on us is R = 5 divided by 20mA.

##### (Side note. mA is = to 0.001 so 20mA is equal to 0,020A. you can take the number and multiply by 10 to the power of -3. It is the same as we go from a meter to a millimeter(mm), exactly the same :))

##### Knowing that we can get R = 5 divided by 20mA will give us 250 ohms. So we now know that we need to put a 250 ohm resistor to make sure our LED does not break.

##### Easy ey!! 🙂

## Resistance Series vs Parallel

##### When we build a circuit, there will be times where we will have more than one resistor in a circuit.

##### So how does having more than one resistor affect our total resistance of the circuit?

##### Well, resistors can be placed in a circuit in two different ways:

- Series
- Parallel

**Series**

##### Series configuration can be seen below. When two resistors are connected one after another, we call it in series. So in the configuration below. The total resistors will be R = R1 + R2. This gives us 200ohm.

##### So to calculate the current through this circuit. We can use the same Ohms law as we discussed on the top.

- V = IxR
- 5V = I/(100+100)
- I = 5V/200
- I = 25mA

**Parallel**

##### Parallel resistor configuration is a bit more tricky, but do not fear, nothing we can not handle, together 🙂

##### You will see a parallel configuration below.

##### The total resistors will be 1/R= 1/R1 + 1/R2.

##### So R = reciprocal of (1/R1 + 1/R2) if you want to learn more about reciprocal click here

##### So to calculate the current through this circuit. We can use the same Ohms law as we discussed on the top.

- V = IxR
- 5V = I/(Recipical of (1/R1 + 1/R2)
- I = 5V/(Rec(1/100+1/100)
- I = 5V/(Rec(2/100)
- I = 5/50
- I = 100mA