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AC vs DC (Alternating Current vs. Direct Current)

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AC vs DC (Alternating Current vs. Direct Current)

Electricity is a type of energy generated by the flow of electrons. The flow of electrons within a closed circuit is called an electric current. This movement of electrons can be inside a conductor such as a wire. The direction of the movement of these electrons decides the type of electric current. Electric current is divided into two – Alternating current and Direct current.

Alternating current (AC) the electric current that changes direction at frequent time intervals and does not follow a steady path. This is why the voltage in AC is reversed periodically as its direction alters. But in Direct Current, the electrons flow in one direction only.
The article below will discuss the details of these two types of currents.

What is Alternating Current?

Scientist Nikola Tesla introduced alternating current to the world. In alternating current, the electrons keep shifting their directions periodically. As a result, the voltage is also reversed along with the current. Also, the magnitude and polarity change with time.

To identify it using a waveform, a sine wave is used and it can be considered as a curved line. The curved lines depict electric cycles that are measured per second. This measurement is read in Hertz.

Using a transformer, AC can be converted from high value to a lower value and vice versa. That is why alternating current is mostly used to power houses, offices, and buildings. Moreover, transporting the current over long distances is relatively easy.

Generation of AC

AC is generated using a device called an alternator. Here, a loop of wire is spun inside a magnetic field. This induces the flow of current along the wire of the device. The rotation of the wire can be caused by flowing water, a wind turbine or a steam turbine. So, the wire spins and periodically enters a different magnetic polarity. As a result, the voltage and current fluctuate inside the wire.

The generated current can be of different waveforms such as sine, triangle, and square. But the sine wave is usually preferred over the other waves as it is easier to generate. The other waves need a separate device to convert them into the required waveform. In some cases, the shape of the equipment has to be changed to generate usable alternating current.

Applications of AC

  • Most of the offices and households use alternating current.
  • Used for powering electric motors. Generators and motors work by using AC to convert the electric energy into mechanical energy.
  • Refrigerators, air conditioners, dishwashers, television sets, and washing machines use AC.
  • Signal transmission for mobile phones, microwaves, and radios.

What is Direct Current?

In direct current, the electricity moves in a single direction with a steady voltage. The frequency of the current is zero and the magnitude remains constant. The intensity of the current can alter with time but the directional movement remains the same. Also, the polarity of the voltage never gets reversed.
The electrons move from the negative pole to the positive pole.

Generation of DC

Direct current is produced by photovoltaic, electrochemical cells and batteries. But as alternating current is the most preferred form of current in the world, it is converted into direct current. DC is generated by a number of ways:

  • A direct current is produced with the help of a device called commutator that is part of an AC generator
  • A device called rectifier converts the alternating current into a direct current
  • Direct current is also developed inside batteries that are due to the result of the chemical reactions inside it

A device called filter is used to remove the current pulsations of the output generated by the rectifier.

Applications of DC

All computers, laptops and electronic devices require direct current to function properly. Solid-state equipment, that is a part of transistors and LED TVs, need 1.5 to 13.5 volts.

Devices that make use of vacuum tubes such as a CRT display, television, a high power radio or a broadcast transmitter require 150 to thousands of volts of direct current.

A power amplifier for radio communications may need more than 100 AMP of direct current. But the range can be almost zero for an electronic watch.

Other devices that use DC include mobile phones, flashlights, electric vehicles and flat-screen TVs where the AC goes into it and is converted into direct current.

Alternating Current (AC) vs Direct Current (DC)

Now let’s take a look at the key differences that separate the two types of currents from each other.


The electrons in a circuit reverse and change their direction in alternating current. In the case of direct current, they flow only in a single direction.

Cause of Electron flow

In AC, current flows by rotating a coil in a magnetic field. It is also possible by rotating a magnetic field inside a stationary coil.

In DC, the electrons flow due to the steady magnetism alongside the wire.


The frequency of a direct current is zero whereas the frequency of the alternating current is 50 or 60 Hz that depends on the standards of the country or region.

Power factor

For alternating current, the power factor is between 0 to 1. The factor remains the one at all times for direct current.

Types of current

The different types of alternating current are sinusoidal, square, triangular and trapezoidal. Pulsating and pure are the two types of direct current.

Current load

The direct current load is always resistive whereas the load for alternating current is inductive, resistive or capacitive in nature.

Distance covered

Alternating current can be transmitted over long distances with a little loss. Transmission of signals over long distances in the case of direct current could entail significant losses.

Generation of current

AC is generated by a device called alternator. A DC is developed by batteries, cells, and generators.


AC is represented by using graphs through square waves, triangular waves, a periodic wave, sine wave and a sawtooth wave. DC can be represented through graphs in the form of a straight line.

Number of substations

The transmission and generation of alternating current need a fewer number of substations. For direct current, a large number of substations are required.


In AC, the magnitude varies with time, but in DC the magnitude remains constant.


Due to its steadiness, if a person is shocked by alternating current, the current will enter and leave the body at regular intervals. Although alternating current will injure the person, if direct current shocks him, the extent of the injury will be more severe. This is because the magnitude in direct current remains the same.

Advantages of AC over DC

The advantages of AC over DC are as follows:

  • Alternating current can be easily transmitted over long distances using a step transformer but direct current cannot be transferred through this method.
  • Generation of alternating current is cheaper than generating direct current. This can be done using an alternator without a split-ring commutator. The device has lower maintenance costs due to high rotation speed.
  • While transmission, the loss of energy is less in AC as compared to DC.
  • A conductor can be used to reduce the magnitude of alternating current without much loss in energy which is not possible in direct current.
  • AC generators are more efficient as compared to direct current generators


We have discussed earlier that in terms of usage, AC is far better than DC as most households use AC. Transmitting alternating current over long distances is convenient and fewer substations are required as compared to direct current.