What is the difference between AC and DC?

An electric current is defined as the flow of charge (electrons).  It can flow through a conductor only when either a return path to the source or path to the earth is available. (Earth can suck all the charge from even a lightening bolt :p ). So, that was an electric current. Almost everybody knows that an electric current can be either AC (Alternating Current) or DC (Direct Current).

What’s AC and DC then?

In an alternating current, the direction of flow of charge reverses periodically. That means the polarity of AC reverses periodically. Whereas, the flow of charge is unidirectional in case of direct currents. Polarity is fixed for DC. The animations below show the directions of AC and DC current.

Alternating Current (AC)Direct Current (DC)

Moreover, waveforms of AC and DC also show the clear difference between them.

AC and DC wave

The above waveforms represent the commonly available AC and DC power supplies. We receive AC power in sinusoidal waveform as shown in the figure above. However, AC power can also be generated in different types of waveforms such as triangular, square-wave etc. for special purposes. DC is straight almost all of the times.

Few more differences between AC and DC are:

  • AC power is generated in power plants by using AC generator (alternator). DC power plants are obsolete today, though DC generators are used to generate DC power wherever required. Batteries also produce DC power due to the chemical reaction taking place into them.
  • The magnitude of AC current changes periodically, so there are different terms of measuring the current (and also AC voltage) such as peak value, average value, RMS value. On the other hand magnitude of DC is fixed, hence no complications.
  • As AC current changes it’s direction periodically, it has some frequency. The frequency of AC is, the number of times direction of flow of charge is reversed per second. While DC has no frequency parameter.
  • The term ‘Power Factor‘ is concerned with alternating current only, due to the effects of inductance and capacitance. Direct current only sees resistance and, hence, power factor is always unity.

These were only few points of differences between AC and DC.  We’ll dive more deeper in our further articles.

Where AC and DC are used?

We see both the types of supplies (AC as well as DC supply) everywhere. We receive AC power supply from an electric company to our homes and offices. The AC supply is standardized as sinusoidal AC with 50 Hz frequency in some part of the world and sinusoidal AC with 60 Hz frequency in the other part. The electric outlets we see in our homes and offices provide AC power supply. Thus, many of our home appliances, such as lights, air conditioners, heaters, etc., run on AC supply. Needless to say, there are endless applications which run on AC supply. Look around and you will find a lot.

DC also find many applications. I’m writing this article on my laptop which uses DC power. Yes! you plug in the charger of your laptop to an AC outlet, but your laptop actually consumes DC. The Chrager, converts AC power in to DC and charges the battery of your laptop. Similar in case of your mobile phone or tablet. That’s not all, DC power finds many applications in industries mostly because of the advantages of DC motors over AC motors.

 

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3 comments

  1. very helpful. thanku. now my question is , what is the parameter that we are generating in the power stations?
    A) Voltage B) Current C) Power

    • Well, all these three quantities are interlinked with each other. You need a better understanding of voltage, current and power. Voltage is generated, and current flows if a closed path is provided. Voltage and current both contribute to power.

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