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Electric current – definition and types

Date of publication: 20-01-2023 🕒 5 min read

AC/DC – I must have heard of it before...

If we asked random people about the abbreviation AC/DC, most of them would probably come up with the name of the legendary Australian rock band. However, the band’s name was derived from an electric device with a plate reading “AC”, which means “alternating current”. Such a short phrase would not be catchy enough for the fans, though, so the band members added the part “DC”, i.e. “direct current”. The name was meant to reflect the electrifying energy of the band’s music, and in fact it would be hard to find a more apt name for them, wouldn’t it?

Still, what’s the point of recalling a rock band’s name in a technical text? The answer is simple: the association with the iconic rock band makes it easy to remember the names of two types of electric current, which is the main subject of this text.

What is electric current? – a simple explanation

The concept of electric current is quite extensive. It requires delving into the physical phenomenon of the flow of positive and negative charges and the interaction of electromagnetic particles. Although seemingly complicated, it turns out to be very logical and easy to understand (at least to the elementary extent that applies to ordinary electricity users). What is electric charge and what does it have to do with electric current?

To make a long story short, electric charge is a physical feature of matter. There are two types of electric charges: positive and negative ones. According to the laws of physics, like (i.e. the same) charges repel each other while the opposite charges attract one another and tend to collide. Therefore, whenever positively charged matter meets something negatively charged, the encounter causes movement that attracts the two. When two positively or negatively charged bodies meet, they repel each other in a phenomenon called Coulomb’s force.

At his point, we reach the core of this problem – electric current is nothing else than the orderly movement of electric charges. How to initiate the movement and have it go in the direction of our choice? How to make the current appear in our electric socket? To understand the physics of electricity, let us clarify the mechanism of particle movement in conductors.

Please, note the keyword in the chapter above! A conductor is an object in which electric charges can move. It is a body full of negative charges awaiting a difference of electric potentials to move them from the higher to the lower potential. Metals are the best conductors that are commonly used for conducting electricity. The reference conductor is copper. Our everyday supply of electricity at home or work is always provided by the same channel, i.e. electric wires. Copper wires are insulated from direct contact, because they might pose a risk of electric shock to human body. Moreover, the insulation separates two phase wires from each other.

Physical quantities characterising the electric current

The fundamental physical quantities which describe the electric current are:

  • Voltage (U);
  • Amperage (I);
  • Resistance (R).

To let you see a clearer picture of that, let us compare the electric current to the flow of water. It will allow us to create a mental picture of the terms.

Let us imagine that water flowing in a pipe is equivalent to an electric current. Amperage, or current strength, is analogous to the flowing water’s speed. The faster the water flows, the higher the amperage is. Voltage is analogous to the water’s pressure. The last part of the puzzle is resistance. It may be considered as the resistance of the pipe walls, thus counteracting the water “attempting” to leak through them. Amperage and voltage are closely intertwined with each other. When the voltage changes, the amperage follows the change. Even if not perfectly synchronised, both quantities always follow each other’s changes. It is Ohm’s law that describes the relationship between these quantities with respect to electric current:

Knowing the basic formula, remember the respective units:

  • the unit of voltage is 1 V (one volt);
  • the unit of amperage is 1 A (one ampere);
  • and 1 Ω (one ohm) is the unit of resistance.

What is the difference between direct current and variable or alternating current?

The fundamental difference that determines the type of electric current is the direction of its flow. Direct current flows in one constant direction while the direction of variable current may change. The most commonly used, specific type of variable current is the alternating current or AC. The direction of alternating current alternates periodically in a strictly organised manner. The number of changes per unit of time is called frequency. In all the electric sockets in the EU, the alternating current has a frequency of 50 Hz. It means that the direction of the current alternates fifty times per second. However, the current described as “variable” may change in any manner and does not have to be orderly.

AC or DC – uses and main advantages

Both types of electric current have distinct features, making them useful for specific solutions. Both direct and alternating currents have some advantages. Let us list the most important features of both solutions:

  • Safety. Direct current shock may lead to burns, but it does not cause a very dangerous condition called ventricular fibrillation. A person exposed to an alternating current shock is less likely to survive than in the case of a direct current shock;
  • Direct current may be accumulated and stored, which makes it useful in batteries, rechargeable (storage) batteries, power banks or chargers, power supplies for laptops or mobile phones. What is more, direct current is also used in cars;
  • Direct current is a perfect solution for electric motors, which need their rotor speed to be regulated. By regulating the supply (input) voltage, we can adjust the rotational speed of the device;
  • A wide array of electronic devices must be powered with direct current. To power those devices, we use proper power supply units which convert alternating current to properly adjusted direct current;
  • Another advantage of direct current is a minor energy loss during long-distance electricity transfers. For electric energy connections transferring power between neighbouring countries, direct current is used;
  • Modern photovoltaic installations generate electricity in the form of DC;
  • However, alternating current has certain flexibility that direct current lacks. For example, using a simple AC transformer can adjust the voltage for any given electric system or device. Therefore, we may expect to have AC electricity of 50-60 Hz frequency (depending on the region) in our sockets;
  • Note that the higher the voltage of transferred AC, the higher energy losses may be expected. To transfer the power from a power plant to end users, the former uses transformers, which transform the high voltage to the safe level of 230 V.

AC or DC – which one is better?

Let us remind you of an interesting historical fact. Two distinguished scientists of the 19th century fought with each other to prove one type of electric current better than the other. These were Thomas Edison and Nicola Tesla. They competed so vigorously that their dispute was sometimes called “a war”. Can we, however, unequivocally decide which one is better? As explained above, both direct and alternating currents have their applications, and if we eschewed any of them, we would end up very limited and devoid of many possibilities. We may only wonder what the world would be like if the pioneers of modern electrical engineering had used their time and efforts for joint research of their concepts; maybe we would be at a completely different point of technology development today...?

Transfer Multisort Elektronik (TME) is one of the world’s largest global distributors of electronic components, electrotechnical parts, workshop equipment, and industrial automation. The catalog includes over 1,500,000 products from 1,300 leading manufacturers. TME’s modern logistics centers in Łódź and Rzgów (Poland), with a combined area of over 40,000 m², ship nearly 6,000 packages daily to customers in more than 150 countries.

TME also invests in the development of knowledge and skills of young engineers and electronics enthusiasts through the TME Education project, and supports the tech community by organizing the TechMasterEvent series, promoting innovation and experience exchange.

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