Electricity is the flow of electric charge and voltage is the force that makes that charge flow. In this article, we will be focusing on the concept of current. It is important to note that there are two kinds of current: Alternating Current and Direct Current. The majority of this article will be focused on Direct Current.

Current

Electric current, or simply current, is the steady flow of electrons. In other words, it is the rate of flow of electric charge or amount of charge that passes a point per unit of time. Current exists when there is a potential difference or a net flow of electric charge that occurs when electrons move from a low potential (negative terminal) to a high potential (positive terminal). 

When electrons move, they carry electrical energy from one place to another. Static electricity and current electricity are like potential energy and kinetic energy. When electricity gathers or stored in one place, it has the potential to do something in the future.

Direct Current was first produced by Italian physicist Alessandro Volta, who invented the first chemical battery known as the voltaic pile in 1799. However, electric current was not understood until Andre-Marie Ampere theorized that current flowed from positive to negative, where positive indicates a surplus of charge and negative indicates a deficiency of charge. 

This theory formed the basis of what is known today as conventional current. The logic behind was that the charges from the positive terminal with a surplus of charge would travel to the negative terminal that has a deficiency of charge. Therefore, conventional current flows from the positive to the negative terminal. While conventional current was used in the standard notation for current flow, it was later explained that charges travel in the opposite direction:

Electron current flow explains how electrons flow in a circuit. Since ‘like’ charges repel and ‘unlike’ charges attract, this theory explains that electrons ‘flow away’ from the negative terminal to the positive terminal. 

Ampere

Current is measured in amperes. Named after French physicist Andre-Marie Ampere, the SI unit for current is called an Ampere (A) or Amp, for short. The Ampere is one of the 7 basic/standard units of the SI system (metric system) of measurements. It can be expressed using the equation:


where I is current in amperes, Q is the quantity of charge (electricity) in coulombs (C) and t is time in seconds.

Therefore, 1 Ampere is defined as the flow of 1 Coulomb of charge per second. 

Current in Context

As mentioned earlier, current is defined as the rate of flow of charge. In other words, it is the rate of flow of electrons. An electron has a charge of -1.602 × 10-19 C. This number is negative because electrons are negatively charged. This means 1 Coulomb of charge has 6.2415 x 1018 electrons and therefore, 1 Ampere is the flow of 6.2415 x 1018 electrons per second. 

Commercial power lines make available about 100 amps to a typical home. Typically, a 60-watt lightbulb pulls about 0.5 amp of current and a room air conditioner about 15 amps.

Once the current gets to the end of the line, most of it is used one of two ways: either to provide heat and light through electrical resistance, or mechanical motion through electrical induction. In this sense, electric current is said to do work.

Direct Current

In simple terms, direct current refers to electric current flowing in only one direction. 

A graph of direct current would look like this: 

This graph represents the output of a DC source. These sources provide a constant voltage over time as the flow of current is unidirectional (alternating current will be discussed in the following article).

Examples of DC sources of electricity include: 

  • Solar Cells
  • Batteries
  • Power Supplies

Anode Vs Cathode

Anodes and Cathodes are terms commonly used to refer to the negative terminal and positive terminal respectively. But this can be misleading. By definition, anode is the electrode through which current flows in from outside while cathode is the electrode through which current flows out (thus the pnemonic ACID, “anode current into device”). But in reality, electrons are repelled by the cathode and are attracted to the anode, which results in the current of electrons flowing from the cathode to the anode This is important to keep in mind because it means that the anode and cathode on a battery are relative to whether the battery is charging or discharging. 

At the end of the day, as long as you are able to differentiate between the positive and negative terminal of a battery, any circuit will work out just fine. However, it is important to remember that the positive terminal will always have a greater potential compared to the negative terminal in terms of a positive charge as the conventional current will always flow from a high to low potential.