What is Alternating Current – Read our Ultimate Helpful Guide

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What is alternating current

Let’s take a deep dive and answer the question ‘What Is Alternating Current?’

We all use electricity every day, but how many of us actually know how it works? In this article, we’ll be looking at the basics of alternating current (AC).[1] This type of electrical current is ubiquitous in the world around us.

But have you ever wondered how the electricity that powers your home or office gets there? In this article, we’ll take a look at the basics of alternating current (AC). We’ll see how it differs from direct current (DC), and how it’s used to deliver electricity over long distances. We’ll also touch on some of the challenges associated with working with AC.

What is Alternating Current?

An alternating current is a current that reverses direction. This means it flows in two directions, forward and backward. This is in contrast to direct current (DC) which flows one way. Alternating current is how our electricity is delivered to commercial premises and homes.

What is Direct Current

A common DC power source is a flashlight battery. It uses direct current because it needs to be battery-powered, and batteries can only produce DC, not AC.

This is because batteries can only produce a unidirectional flow of electrons. This is in contrast to the alternating flow transmitted through the grid.

How do we use Alternating Current?

Electric utilities produce an alternating current. They transmit this to homes and businesses through the grid.

The US national grid is the world’s largest alternating current system. It has over 8,835 miles (14,200 km) of high-voltage transmission lines. It carries electricity at voltages up to 765,000 volts (765 kV).[2]

This grid delivers electricity by transforming it to extremely high voltages. This means that it can be transmitted across long distances. The power is then transformed to lower voltages near the end user.[3]

How is AC Current Produced

A device called an alternator produces an alternating current. An alternator is a machine that converts mechanical energy into electrical energy.[4] The most common type of alternator is the internal combustion engine-driven alternator. This is used in automobiles and other vehicles.

The internal combustion engine in a car or truck turns a crankshaft. In turn, the crankshaft rotates an electromagnetic field inside the alternator. This rotating electromagnetic field induces a current in the alternator’s output winding. It is this current that is AC.[5]

The national grid uses the same principle to generate electricity on a much larger scale. The most common type of power plant in the US is the coal-fired power plant. In a coal-fired plant, coal is burned in a boiler to produce steam. This steam is then used to turn a turbine, which drives an alternator to produce electricity.[6]

The electricity is transmitted at high voltages over long distances to population centers,

How it works

The basis of AC power is electromagnetic induction. When a conductor moves through a magnetic field, it develops an electromotive force (EMF), or voltage. It is proportional to the speed of the conductor through the magnetic field. The direction of the EMF will be perpendicular to both the magnetic field and the direction of motion of the conductor. This is the principle of operation for the alternator in an automobile.

The Basics of Alternating Current

An alternating current is an electric current that reverses direction. This contrasts to direct current (DC) which flows only in one direction. Electronic devices such as computers and portable electronics use DC power. The AC delivered to your home (in the US) has a frequency of 60 Hz. This means that the current changes direction 120 times per second.[7]

The Advantages of Alternating Current

Alternating current has several advantages over direct current.

First, AC can be generated at very high voltages. This is important for long-distance electricity transmission.

Second, a transformer can transform AC power into different voltages. This is important because different loads need different voltages. For example, appliances in your home operate at 120 volts. While the electric motors in an industrial factory may operate at 460 volts.

Transformers enable the use of the same current to power both your home and the factory.

Finally, AC is simple to generate using an alternator. We can locate AC power stations anywhere that there is a source of mechanical energy. These include where there is running water, a tide, or wind. A wide variety of power plants are suitable for its production. These include coal, nuclear, hydro, and renewable sources such as solar and wind.

The Disadvantages of Alternating Current

The residential sector uses alternating current for most of its needs. This is because the majority of electronic devices in the home operate on AC power. AC power is also used in the commercial sector for the same reason. But there are some disadvantages to using AC power.

First, AC power is not easy to store. Batteries are the most common means of storing DC power, but they are less efficient at storing AC power. This is because the polarity of AC flips between 50 to 60 times a second, making it impossible to store.

Second, AC power can be more difficult to control than DC power. The constant switching of poles makes it hard to tame.

This is a problem. When AC current flows through a conductor, it produces a magnetic field around the conductor.[8] This magnetic field can interfere with the operation of electronic devices. Most electronic devices operate on DC power for this reason.

And third, AC power can be more dangerous than DC power. The voltage in an AC circuit can be very high. It can cause serious injury or even death if a person comes into contact with it. DC current, while a little safer, can still be very dangerous in certain circumstances. They are similarly dangerous at the same voltage, but DC is usually at 12 Volts which is less dangerous.[9]

Whereas we use a chemical reaction, like the reaction inside a lead-acid battery, to produce DC. The advantage of this is that we can access DC power in a wide variety of locations. This includes remote and inaccessible locations where AC generation is impractical.

The Applications of Alternating Current

We use alternating current in a wide variety of applications, including

  • Air conditioning
  • Automotive systems
  • Computers
  • Electric lighting
  • Electric motors
  • Industrial machinery
  • Power distribution
  • Railroad systems
  • Telecommunications
  • Transformers

The Theory of Alternating Current

The AC power system consists of three parts. The generator, the transmission system, and the distribution system.[10] The generator is the device that converts mechanical energy into electrical energy.

The transmission system is a network of high-voltage power lines. They carry electricity from the generator to the distribution system. The distribution system is a network of lower-voltage power lines. They carry electricity from the transmission system to the end user.

The Basics of Direct Current

Direct current is an electric current that flows in one direction only. It is the form used in batteries and devices like computers and portable electronics. The DC delivered by a battery has a constant voltage. The current does not change direction.

The Advantages of Direct Current

Direct current is preferable for use in

  • Batteries
  • Computers
  • Portable electronics
  • Telecommunications

This is because DC can be easily stored in batteries and can be more easily controlled than AC. It is less likely than AC to cause interference with electronic devices. This is why our laptops and other devices have an AC adaptor. This converts the AC to DC which is more suitable for the device.

The Disadvantages of Direct Current

There are some disadvantages to using direct current.

First, DC cannot be easily generated at high voltages. This is a problem because high voltages are necessary for long-distance electricity transmission.

Second, DC cannot be easily transformed to different voltages. This is important because we need different voltages for different loads.

Transformers enable the use of the same alternating current to power your home and your factory.

DC is also more expensive than AC at scale. This is because the process of stepping up and stepping down the voltage is much more complex and thus more expensive than AC.

DC power is not as easily distributed as AC power. This is because more energy is lost with DC current than with AC during transmission.

Finally, DC power is not as easily converted to other forms of energy, such as mechanical energy or heat, as AC power.

History of Alternating Current

The first device to produce Alternating Current was invented in the early 19th century by Hippolyte Pixii, a French instrument maker. Using the ideas of Michael Faraday, he connected a spinning magnet to an induction coil. This produced a current which changed direction as the magnet rotated.

In later years,

  • Thomas Edison developed a successful direct current system
  • Nikola Tesla developed AC electricity as we know it
  • George Westinghouse improved AC transformer technology

Alternating Current became increasingly popular in the late 19th century. This is because it won the war of the currents.[11] In this battle, Thomas Edison advocated for direct current. Nikola Tesla advocated against his boss for alternating current.

Alternating current won because it could be transmitted over long distances. This is because Westinghouse developed an AC transformer. This transformed the high-voltage AC into a low-voltage AC. This made it safe for use in homes. And in the late 19th Century the first hydroelectric dam was constructed at Niagara Falls. This supplied power to Buffalo, New York using alternating current.

Conclusion – What is Alternating Current?

We’ve deep-dived into the world of alternating current and I hope you have found this illuminating. It just goes to show the incredible achievements of our civilization that we have been able to come from nothing to transform the very way we use and generate electricity.

It is truly incredible how much we have achieved but I know that there are many more incredible achievements to make and I can’t wait to see what they are. Thank you for joining us on this journey of discovery.

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Steve Brown


Steve is a gadget enthusiast who's always been intrigued by batteries. The founder and editor of Battery Chargers Info, he's assembled a group of like-minded experts to cover every facet of portable power His aim is to help you learn more about your favorite gadgets and their batteries so you can maximize both their performance and their life. Follow him on Twitter: @batterycharge1

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