DC Circuits Fundamentals of Electricity

Alternating Current (AC) vs. Direct Current (DC)

Electric current is the amount of electric charges that passes through a wire with respect to time. When battery is connected across a conductor, electrons move from negative terminal to positive terminal of battery. They move with very high velocity (more than the speed of light) and thus produce some amount of heat energy. Due to this, light bulbs glow.

Electric current is categorized into two types: Alternating Current (AC) and Direct Current (DC). The difference is that direct current flows in one direction while alternating current changes its direction rapidly. Both AC and DC have their own specific uses but AC is the more common type of current that we use today at home, offices, etc.

Nikola Tesla and Thomas Edison invented AC and DC respectively. They battled over the standardization of the current notation. After all AC won the battle when it powered France Fair and finally, it came into existence.

Alternating Current (AC)

An electric current is current that reverses its direction many times a second at regular intervals. It is typically used in power supplies. A number of times the current changes its direction in one second can be defined as the frequency of AC. 50Hz. frequency means it changes 50 times in a second. Frequency in the USA is 60Hz. while in India it is 50Hz.

AC is generated by devices called alternators. An alternator is a machine that converts mechanical energy into alternating current. It works on the principle of Faraday’s law of electromagnetic induction. Here mechanical sources of mechanical energy include steam turbines, internal combustion engines, and water turbines. Today generator provides nearly all of the power for electric power grids.

AC waveform

AC can be represented by many waveforms like a triangular wave, square wave but the most common representative is a sine wave. It is represented by amplitude and time. Amplitude is the peak value of the current.

Alternate Current AC - Sine wave

AC Waveform

Applications of AC:

AC is widely used in industries of transportation and production of electricity. Almost every house is powered by AC. AC is also used to power electric motors. DC is not used to power houses due to high risk of cost, and converting voltages.

Advantages of AC:

  • AC is easy to generate than DC.
  • It is cheaper.
  • The loss of energy during transmission is negligible.
  • AC can be easily converted to DC.
  • It is easy to transmit.
  • In AC, resistance is greater than DC.

Disadvantages of AC:

  • At high voltage it is dangerous to work with AC as the shock of AC is attractive but the shock of DC is repulsive in nature.
  • AC is not efficient and needs power factor management for efficiency.
  • Most of the gadgets do not run directly on AC.

Direct current (DC)

Direct current refers to electric charges flowing in one direction. This type of current is most commonly produced by batteries.

DC waveform

DC circuits have a unidirectional flow of current and like AC it is not changing the direction periodically.

Waveform of DC is a pure sine wave. As you can see, the voltage is constant with respect to time.

Direct Current DC waveform

DC Waveform

Applications of DC:

DC power is widespread in low voltage applications such as charging batteries, automotive applications, and aircraft applications and in almost all electronic gadgets like mobile phone, music players, etc.

Conversion of AC into DC:

We get DC from the following things:

  1. Batteries, in which chemical reactions happen and then this chemical energy is converted into electrical energy.
  2. AC to DC conversion via a rectifier. Rectifier is an electronic circuit which converts AC into DC. These rectifiers can be seen in our mobile chargers, battery eliminators, etc. Most of the gadgets are powered or charged indirectly by AC and then this AC is converted to DC.

AC and DC sources:

Alternating current and Direct current source can be denoted by these symbols.

AC and DC voltage source symbol

AC and DC voltage source symbols

The direction of current changes at a regular interval of time in AC source while in DC source change in direction is constant. You can see the difference in the figure below:

Alternating Current AC and Direct Current DC - Direction of current

Direction of Current

Advantages of DC:

  1. It is able to power most electronic gadgets.
  2. It is easy to store DC.
  3. DC is less dangerous than AC because chock of DC is repulsive.

Disadvantages of DC:

  1. It is costlier to produce.
  2. It is difficult to transport.
  3. It is difficult to generate DC as compared to AC.

Alternating Current (AC) vs. Direct Current (DC)

Thomas Edison proposed a network of power plants which produced DC power and they could power houses nearer to 1 mile from that power plant. DC is very difficult to transport from one place to another. So Tesla came up with AC power but Edison considered this type of current as extremely dangerous. Westinghouse then worked on power distribution system using Tesla’s patents. AC can be easily transported from one place to another using a transformer. This can power to houses many miles away from power houses and thus can reach to more number of people. AC finally came into existence when it powered France Fair successfully.

Difference between Alternating Current (AC) and Direct Current (DC)

The main difference between AC and DC is their directions. AC changes its direction in regular interval of time while DC is unidirectional flow. Due to many advantages of AC, it used to power our houses and offices while DC is used to power low power devices. AC is easier to transform between voltage levels, which makes high-voltage transmission more feasible. DC, on the other hand, is found in almost all electronics.


Thus, AC and DC are two types of electric current. Both have their own uses, advantages, and disadvantages. AC is more widely used to power buildings and offices while DC is more widely used to power electronic gadgets. Our lifestyle is dependent on both of them.

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