Electric current in general
1. An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is one of the 7 fundamental base SI units defined in terms of the charge on the electron and the second derived from a transition frequency of the cesium atom and is expressed as Coulombs/second, called an Ampere or amp.
2. While it is not a vector, it has a direction defined to be the direction a positive charge would flow, for example from a higher electric potential to a lower potential. [This can be confusing at first because in most circuit applications the negative charges are actually moving, but the direction of the current is considered to be in the opposite direction of the movement of negative charges.]
3. It is a key phenomenon in electricity and magnetism in that current responds to electric and magnetic fields and also generates magnetic fields.
Electric current dependence on voltage and resistance
1. When current flows within electrical conductors, typically called a circuit, an Ohmic circuit is defined as one in which the current is instantaneously given by Ohm’s law,
I = V/R, where V is the voltage difference across the circuit or circuit element and R denotes its resistance. This means that current instantaneously increases with voltage linearly and depends inversely on the resistance.[Note that this is not the case if capacitors, inductors, or semiconductors are involved.] In addition, the power dissipated by the current flowing in the circuit can be expressed in various formulas in terms of I, V and R.
2. Wires and connections in circuits are generally made of materials of low resistance, which often can be neglected in calculations of circuit characteristics. Resistors are components designed to have specific values of resistance when connected in a circuit.
3. If the voltage in a circuit is constant, the circuit is called a DC (direct current) circuit. If the voltage changes with time, often sinusoidally, the circuit is called an AC (alternating current) circuit.
4. Analysis of resistors in DC circuits is a fundamental skill needed to evaluate electrical circuits and involves calculating the equivalent resistance of sets of resistors connected in series or in parallel.
When I tried to put some graphic summaries in this answer box, it saw them as too large so I made a video just to show them. If you want I can probably just send you the graphics here via a message. My students find they read the text I use relatively little and can understand everything from the graphics I provide. The graphics here summarize this electric current information and give the key things you need to know. I also include an example problem frequently given on combining resistors in series and parallel. One very common simple mistake students and others make is forgetting to take the reciprocal after calculating the equivalent resistance of resistors in parallel. I can almost guarantee you will make that mistake unless you use an easy way to remember not to. I can help you avoid that mistake like I have helped my students over the years by giving you some ways to make sure you don't.
