What is Electricity?
Electricity is another form of energy transferred through a flow of charge by the movement of electrons. The flow of charge is called current and is measured in Amperes with symbol A. There are two types of electrical signals, the first one is called Alternating Current (AC) and the other one is called Direct Current (DC). Alternating current flows continuously in both negative and positive direction as can be seen in the image below. AC is commonly used to transfer power from power stations to residences, businesses and it is the form of electrical energy used by most appliances like a TV, Computer or a Fridge. The advantage of using AC is that it is an efficient way of transmitting power because the voltage can be stepped down/up during the transmission.
With DC, current electricity flows in one direction from the highest potential energy point to the lowest, so in other words, we need power or energy for charges to flow or to have current. The electrical potential energy required is called Voltage and is measured in Volts (V). We get electrical energy from many sources, for DC applications we usually get it from batteries or adapters that can convert AC to DC.
Understanding electrical circuits
Now that we know what electricity is, we need a way to control it to perform specific tasks like a TV, Computer, Washing machine, Lights, etc. We do this by designing something called a circuit. A circuit is simply a connection of electronic components that allow current to flow in a closed path connected using conductors. Conductors are materials that allow current to flow past them, commonly used conductors are copper electrical wires. All electrical components have a quantity called resistance, some more than others and others its insignificant. Resistance reduces the flow current, so we use resistors to limit current because not all electrical components use the same current. Materials that have the highest resistance are called insulators, it means that for all practical purposes electricity cannot flow through them. A short circuit is when there is nothing restricting the current flow and as a result, the current tries to be infinite and ends up damaging electrical components. Once again in order to have current we need a power source, so a circuit cannot work without a power source.
Ohm’s law is named after the German physicist who first discovered the relationship between Current, Voltage and Resistance. Ohm’s law basically states that for any given DC circuit the amount current that flows through a conductor is directly proportional to the voltage applied across it and inversely proportional to the resistance at a constant temperature. The relationship can also be expressed algebraically I=V/R and to make it easy to understand you can use the chart below as a mental model to remember the relationship.
To illustrate Ohms law we will use a circuit with a battery, resistor, and an LED. The LED is rated 20Amp meaning that if current above this threshold passes through to the LED, it might blow up. If we have 9V voltage, what is the minimum resistance required so that the LED will light up and not blow up? To calculate this we will use Ohms law. We have V=9V, we have I=20mA so now the only unknown variable is R, from basic algebra we know that R=V/I=9/20e-3 =450 ohms
The answer is that it will require a minimum of 450 ohms in order to safely power the LED. Watch the video above to see the actuall cirucuit being built.