Before we begin..
Welcome everyone! In the post today we will be laying a few ground rules for the basis of our learning, as well as going over essential terms, units of measurement, and formula’s.
Most of these posts will be in the form of me trying to explain to the reader how something works. I’m sure I will make mistakes along the way or have an incomplete picture at times, but please do feel free to enlighten me with knowledge. That, after all, is what I am here to do! And hopefully help the readers too!
Unless specifically noted, most of the learning will be related directly to DC. I will use examples of AC as well, but the examples will be specifically noted.
As for sources I am using mostly books! As well as a website here or there that will be linked when applicable. I also work with electricity as an Audio Engineer so some examples will be from the perspective of how I utilize them for production. The book I have been using the majority of the time to study with and learn from has been “Make: Electronics” 2nd edition by Charles Platt.
So how does Electricity work?
Well, think back to Physics class. Remember how inside every atom there is a nucleus, and orbiting every nucleus are electrons? Turns out those guys are pretty important. Electrons jumping from one nucleus to another along a path (e.g. wiring) to reach the next device (e.g. LEDs or resistors) on its path is what is regarded as the flow of electricity.
A common misconception is that electricity moves from positive to negative. This however is false. Electricity actually moves from negative to positive, however if you were to imagine the flow from positive to negative the rules of physics would apply the same, and so the misconception continues to occur.
The reason electricity moves from negative to positive is that it is electrons (with a negative charge) that are starting together and move toward protons (positive charge) with spaces available for the electrons to situate comfortably.
Important units of measurement
Voltage – The amount of electrical pressure in a circuit (Volt, V).
Ampere – The rate of electricity flowing in a circuit (Amps, I)
Ohms – The amount of electrical resistance (Ω, R)
These 3 variables are essential to understanding electricity, and are the basis of Ohm’s Law.
V = I x R Voltage = Current (multiplied by) Resistance
I = V / R Current = Voltage (divided by) Resistance
R = V / I Resistance = Voltage (divided by) Current
It should also be noted that typical units of measurement maybe very small or very large. An example of this would me milliamps (mA). A milliamp is 1/1000 of an amp. Say we have a current that has a value of 20 mA. To be able to plug that number into an equation we must first convert it into amps. Simply move the decimal place 3 spots to the left, so 20 mA would become 0.02 amps.
Similarly with ohms, a typical unit of measurement you will see will be kilohms. a kilohm is measured when the resistance is over 1,000 ohms and is abbreviated with a “K”. For example, 1,500 ohms would be written as 1.5K ohms.
Volts also has smaller and larger measurements. The measure of millivolts (mV) is 1/1,000 of a volt and the measure of a kilovolt (kV) is when you have more than 1,000 volts. 1,000mV = 1V = 0.001kV
Now that we have our units down, lets try using Ohm’s Law
Say we would like to power an LED with a 9V battery. A very simple circuit.
Circuit – A completed pathway for electrons to flow
LED – Light Emitting Diode, device that lights up when voltage is applied
The LED we have chosen to use is rated by the manufactured to run at 2V potential difference at 20mA.
What is potential difference you may ask? Potential difference is the amount of volts between two specific points in a circuit, like the start and end of an LED. The potential difference across ALL devices in a circuit should always be equal to the value of the supply voltage, in this case our 9V battery.
So if we try to use an LED just hooked up to a battery, we would get no light, because the LED only has a potential difference of 2 Volts. We need to add another device into the circuit to make a complete 9 Volts. For this we will use a resistor.
Resistor – device used to restrict Voltage and Current<– Resistor
Another thing that is very important to note is that the current will be the same through every point on the circuit, whether you are measuring an LED, a resistor, a potentiometer, or any other device.
So if we have a 9V supply and 2V will be used on the LED, we can determine that the device we add should have a Voltage of 7
9V – 2V = 7V
And we also know that the current will be 20mA thanks to the manufacturers rating of the LED
So with this information we can find how many ohms of resistance is needed from the resistor to complete the circuit. Lets use Ohm’s Law.
R = 2V / 0.02 amps
R = 350Ω
The resistor that we need in order to complete the circuit will need to be rated to handle 350Ω
And there we have a completed circuit, with a battery, LED, and resistor!
That’s about all we will go into for now, if you have any questions or comments, please feel free to comment or shoot me an email at firstname.lastname@example.org