What's the difference between AC and DC?

What's the difference between AC and DC

You’ve probably heard the terms alternating or direct current or seen the AC and DC marking on your electronic devices. While the current itself is more or less understandable, its types may cause a wide array of questions. What’s the difference between them? Which is better? To make everything clear, let’s start with the basics.


  1. What’s current?
  2. What’s the difference between AC and DC?
  3. AC vs DC - Which is better?
  4. How to determine AC/DC

What's current?


This definition as well as the tens of its variations can be found in most textbooks, but usually, this term is not enough to understand how the electric current is generated and where it comes from. To have a better understanding of how it works, let’s take a look at the model of an electrical circuit (Picture 1). This circuit consists of a power source, a light bulb, and a copper wire that represents a conductor.

The atoms in a conducting material have free electrons that randomly move from one atom to another (Picture 2).

To produce electricity, we need to force these electrons to flow in the same direction (Picture 3). This can be implemented by connecting a power source, such as a battery, that creates voltage. To put it simply, this voltage “pushes” free electrons through a conductor right to the light bulb, producing light and heat.

What's the difference between AC and DC?

Depending on the direction the electrons flow, electric current can be either direct or alternating.

Direct Current (DC)


The electrical circuit illustrated above is a good example of how DC can be produced. The electrons in this circuit always pass in the same direction from the cathode to anode (Picture 4).

Alternating Current (AC)


In contrast to batteries, some power sources (e.g. generators), produce the current that cyclically changes directions, moving back and forth (Picture 5).

As the flowing stops before changing its direction, the power supply to a device will stop for a fraction of a second as well. It can be seen in the slow-motion video of a light bulb connected to an AC power source. In this electrical circuit, the bulb is constantly flickering, even though it is invisible for a human eye under normal conditions as the flickering is too fast for us to notice it.

AC vs DC - Which is better?

Actually, it’s hard to answer whether AC or DC is better. Each type has its pros and cons, making them perfect for specific applications. As the electrons in AC alternate around 60 times per second (the standards vary throughout the world), it is inappropriate for most of the modern devices that are extremely sensitive to power changes. Connecting them to a generator, for instance, will cause irreparable damages to the devices as well as to the whole circuit. Thus, all washing machines, printers, computers, and phones have special AC adapters that enable all the components to work properly.

Direct current can power practically all the electronic devices we use. Wouldn’t it be easier to transmit DC instead of AC and forget about all those adapters? The answer is simple - no. And there is a significant reason for that.

Cities, towns, and villages all over the country need enormous amounts of electrical power. To make this power affordable, it is distributed at very high voltages, which are far higher than those we can safely use in our homes. In other words, before we can safely use the power, we have to reduce the voltage somehow. Some electrical devices, known as transformers, are able to change the voltage of AC either up or down. Due to the direct current nature, transformers cannot change DC voltages, thus transmitting DC this way becomes impossible. Moreover, DC transmission systems are a lot more expensive and less durable as the wires should be much thicker to deliver the same amount of power, while still are more likely to wear out in a comparatively short period of time.

How to determine AC/DC

As a rule, all the devices have a special marking showing whether the outputs are AC or DC, but sometimes it happens that there is no information given. In this case, to determine AC or DC, you’ll need a multimeter or at least a DC voltmeter. Just connect it to the output and look at the readings. If there is no deflection, then the output is AC and vice versa.

Designed to measure volts, amps, and ohms, multimeters are necessary for any type of electrical work. They come in various types and form factors, including a clamp-on meter that is known to be one of the most efficient current diagnostic tools capable of measuring current without direct contact with it. At Mega Depot, you can find an extensive variety of high-quality multimeters as well as other test equipment from the most trusted brands.

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