What is Alternating Current (AC) And Direct Current (DC) and Its Applications

Both Alternating Current and Direct Current describes the two types of current flow in a circuit. In direct current, the electric charge or current flows in one direction. In alternating current, the electric charge changes direction periodically. The voltage in AC circuits also sometimes reverses because the current changes direction. Most of the digital electronics that you build by using DC. However, it is easy to understand some AC concepts. Most houses are wired for AC, so if your idea to connect your Tardis melody box project to an outlet, you will need to convert AC to DC. AC also has some useful properties, such as being able to convert the voltage levels with a single component like as a transformer, which is why initially we have to chosen AC means to transmit electricity over long distances.

What is Alternating Current (AC)

Alternating current means the flow of charge that changes direction periodically. As a result, the voltage level also reverses along with the current. AC is used to supply power to houses, buildings, office, etc.

Generating AC

AC can be produced by using a device is called as an alternator. This device is a special type of electrical generator designed to produce alternating current.

Generating Alternating Current
Generating AC

A loop of wire is rotated inside of a magnetic field, which induces a current along the wire. The rotation of the wire comes from different resources like a steam turbine, a wind turbine, flowing water, and so on. Because the wire turns and enters a different magnetic polarity periodically, the voltage and current alternates on the wire. Here is a small animation showing this principle:

To generate AC in a set of water pipes, we connect a mechanical characteristics of a piston that moves water in the pipes back and forth (our “alternating” current).

Waveforms

AC can come in a number of waveforms, as long as the current and voltage are alternating. If we hook up an oscilloscope to a circuit with AC and plot its voltage, over a long time we might see a number of different waveforms. The sine wave is the most common type of AC. The AC in most homes and offices has an oscillating voltage that produces a sine wave.

Sine Wave
Sine Wave

Other forms of AC include the square wave and the triangle wave. Square waves are often used in digital and switching electronics and also test their operation.

Square Wave
Square Wave

Triangle waves are useful for testing linear electronics like amplifiers.

Triangle Wave
Triangle Wave

Describing a Sine Wave

We often need to describe an AC waveform in mathematical terms. For this example, we will use the common sine wave. There are three parts of a sine wave: frequency, amplitude, and phase.

Looking at just voltage, we can describe a mathematical equation of sine wave:

V (t) = Vp sin (2πft + Ø )

V(t) is our voltage as a function of time, which means that our voltage changes as time changes.

VP is the amplitude. This describes the maximum voltage that our sine wave can reach in either direction, means that our voltage can be +VP volts, -VP volts.

The sin () function indicates that our voltage will be in the form of a periodic sine wave, which is a smooth oscillation around 0V.

2π is a constant that converts the frequency from cycles or in hertz to angular frequency (radians per second).

f indicates the frequency of the sine wave. This is given in the form of hertz or units per second.

t is our dependent variable: time (measured in seconds). As time varies, our waveform varies.

φ describes the phase of the sine wave. Phase is a measure of how shifted the waveform is with respect to time. It is often given as a number between 0 and 360 and measured in degrees. Because of the periodic nature of the sine wave, if the waveform is shifted by 360° it becomes the same waveform again, as if it was shifted by 0°. For simplicity, we sill assume that phase is 0° for the rest of this tutorial.

We can turn to our trusty outlet for a good example of how an AC waveform works. In the United States, the power provided to our homes is AC with about 170V zero-to-peak (amplitude) and 60Hz (frequency). We can plug these numbers into our formula to get the equation

V (t) = 170 sin (2π60t )

We can use our handy graphing calculator to graph this equation. If no graphing calculator is available we can use a free online graphing program like Desmos.

graphing calculator

Applications

Home and office outlets are almost always used in AC. This is because generating and transporting AC across long distances and relatively easy. At high voltages like as over 110kV, less energy is lost in electrical power transmission. Higher voltages mean lower currents, and lower currents mean less heat generated in the power line due to resistance. AC can be converted from high voltages easily using transformers.

AC is also capable of powering electric motors. Motors and generators are the exact same device, but motors convert electrical energy into mechanical energy. This is useful for many large appliances like refrigerators, dishwashers, and so on, which run on AC.

What is Direct Current (DC)

Direct current means the unidirectional flow of electric charge. It is produced from sources such as batteries, power supplies, solar cells, thermocouples or dynamos. Direct current may flow in a conductor such as a wire, but can also flow through insulators, semiconductors, or vacuum as in electron or ion beams.

Generating DC

DC can be generated in a number of ways

  • An AC generator prepared with a device called a “commutator” can produce direct current
  • An AC to DC conversion of a device called a “rectifier”
  • Batteries provide DC, which is generated from a chemical reaction inside of the battery

Using our water analogy again, DC is similar to a tank of water with a hose at the end.

Generating Direct Current (DC)
Generating DC

The tank can only push water one way: out the hose. Similar to our DC-producing battery, once the tank is empty, water no longer flows through the pipes.

Describing DC

DC is defined as the “unidirectional” flow of current; and the current flows only one direction. Voltage and current can vary over long time, so the direction of flow does not change. To simplify things, we will assume that voltage is a constant. For example, A battery provides 1.5V, which can be described in mathematical equation as:

V(t) = 1.5V

If we plot this over time, we see a constant voltage

Plot of DC
Plot of DC

The above graph means that we can count on most DC sources to provide a constant voltage over time. Actually, a battery will slowly discharge, meaning that the voltage will be drop as the battery is used. For most purposes, we can assume that the voltage is constant.

Applications

All electronics projects and parts for sale on SparkFun run on DC. Everything that runs off of a battery, plugs into the wall with an AC adapter, or uses a USB cable for power relies on DC. Examples of DC electronics include:

  • Cell phones
  • Flashlights\
  • The LilyPad-based D&D Dice Gauntlet
  • Flat-screen TVs (AC goes into the TV, which is converted to DC)
  • Hybrid and electric vehicles

Thus, this is all about what is an alternating current, direct current and its applications. We hope that you have got a better understanding of this concept. Furthermore, any doubts regarding this concept or any electrical and electronic projects, please give your valuable suggestions by commenting in the comment section below. Here is a question for you, what is the difference between an alternating current and direct current?

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