Electronics Fundamentals

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.


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 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 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
Please note this is the current of the whole system. Please Note the current going through each resistor. Because each resistor is 100R, the current will split through evenly through the branches. So 50mA each
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