Current, voltage and resistance are basically the three things we need when analyzing a circuit. An electrical circuit is basically a path that can conduct electricity, in other words, it is a path that allows free electrons to flow, just like water flows in a river. And this movement of free electrons in a circuit /medium is called “electric current” (sometimes just “current”). The conventional symbol for current is I, and its SI unit is Ampere (written as “A” in calculations). Voltage is the electrical energy per unit charge, and can be regarded as the potential “electrical” energy between two points in a circuit. The unit of voltage is V (Volt). Friction occurs in every movement, and it is something that prevent objects from moving. And the resistance in a circuit does the same thing. Electrical resistance prevents current from flowing. We need to consider resistance all the time because electrical resistance causes energy loss, just like friction causes energy loss. So power factory has to produce a little bit more electrical electrical energy before they send to us because there is energy loss during the transfer of electricity through the wire.Electrical energy loss caused by resistance is in terms of heat, and that is why wires can get very hot after long time usage, motherboards in computers will get fried up by heat if no fans are installed. We use symbol R to represent electrical resistance, and its unit is Ohm (Ω).