Industrial Electronics

# Electric current explained

04 November 2022
Figure 1: Electric current has become the heart of many technologies today. Source: BillionPhotos/Adobe Stock

In 1820, Michael Faraday discovered that electric current could be produced by passing a magnet through a copper wire. And since then, electricity (and electric current) has become the heart of many technologies, where it is being used to energize equipment.

But what exactly is an electric current, how does it work and what is its effect on electrical systems? This article answers all of these questions and more. It will serve as a guide for those looking to understand the basics of electric current (and electricity).

## What is electric current?

Electric current is the flow of electric charge in a circuit. For charges to flow in an electric circuit, two conditions must be met.

1. There must be an energy source (for example, a battery) to create an electric potential difference.

2. The charges must move in a closed conduction loop.

To better understand electric current, consider a simple household water distribution system that features a water pump, a reservoir (storage tank) and connecting pipes.

The flow of water through the pipes is a lot like how charges move in a circuit. For example, the connecting pipes act like wires (or conductors) in an electric circuit, and the water pump acts similar to the battery by releasing energy. The pressure differential generated by the pump as it drives water through pipes is similar to the potential difference generated by the battery (or power source) to move charges in an electric circuit. Finally, the water flow rate in the pipe is similar to the rate at which electric charges move in an electric circuit (which is the electric current).

As such, electric current, I, is defined as:

Where:

I = electric current (Amperes or Coulomb (C) per second)

Q = quantity of charge passing through an electric circuit or a conductor (C).

t = time at which the charge passes through the conductor (sec).

## Electron flow versus conventional current flow

Electrons are negatively charged. Thus, according to Coulomb’s law, they tend to be attracted to positive charges.

In an electric circuit, electrons flow from the negative terminal through the circuit to the positive terminal of the source (for example, battery). But by convention, electric current is assumed to flow in the direction a positive charge will flow (which means from the positive to the negative terminal of the source, as shown in Figure 1 below).

Figure 1: Electron flow versus conventional current flow in a circuit. Source: Aernous8817/CC SA 4.0

## Types of electric current

Electric current is divided into two types based on the flow of charge: direct current (DC) and alternating current (AC).

Figure 2: AC versus DC. Source: Circuit Basics

### 1. DC

As its name implies, this is a type of current in which the electric charge moves in one direction. DC sources include batteries and cells used to power rechargeable devices like laptops and cell phones.

### 2. AC

This is a type of current whose magnitude changes continuously, and direction reverses periodically throughout time, as shown in Figure 3. The frequency of an AC (which is the number of times the electric current changes its direction in one second) is typically either 50 Hz (in Europe) or 60 Hz (in the U.S.).

Figure 3: Typical AC waveform. Source: Temitayo Oketola

AC is used in transmitting electricity over long distances primarily because AC can easily be converted to high or low voltage (with little power losses) using transformers. AC sources play an essential role in powering domestic kitchen appliances, fans and televisions. They are also used for industrial devices like electric motors.

However, AC can be converted to DC using a rectifier, while DC can be converted to AC using an inverter.

## Effects of electric current

When an electric current flows through wires or electrical conductors, some effects are produced due to this current flow.

### 1. Heating effect

Most wires (or electrical conductors) have some level of resistance (which means they resist the flow of electric current). As a result, heat is produced by these wires when electric current flows through them. The amount of heat produced depends on the magnitude of electric current, the resistance of the wire, and the time for which the current flows, according to the equation below:

Where:

H = Heat energy (Joule)

I = amount of current (Amperes)

T = time for which the current flows (seconds)

From the equation above, it can be observed that conductors with higher resistance produce more heat. Likewise, increasing the amount of current flowing through the conductor causes the heating effect to increase.

This principle applies to electric heating appliances like boiling rings, light bulbs and immersion heaters. For instance, consider an immersion heater used to heat water. Suppose the heating element has a resistance of 25 Ω, and 10 A of electric current is allowed to flow through it for two hours. In that case, the amount of electrical energy converted to heat energy can be estimated using:

### Magnetic effect

When current passes through a conducting wire, a magnetic field is produced around it perpendicular to the flow of current. This is the magnetic effect of current, and it causes the wire to behave like a magnet.

This magnetic effect of electric current is useful in electromagnets found in electric motors, generators and electric bells.

## Conclusion

Understanding what electric current entails is important before designing and developing electrical systems that work as expected. While this article presents helpful information about electric current, there is more to electric system design than meets the eye. For example, technicians also need to understand the different types of AC sources and power requirements.