Difference between Alternating Current and Direct Current

Differences AC & DC Supply Electronics & Electrical

The directed flow of electrons or charge in an electric circuit is known as electric current. Based on the nature of flow of electrons (or electric current), the electric current is classified into two types: AC (Alternating Current) and DC (Direct Current). Go through this article to find out more about AC and DC and how they are different from each other.

What is Alternating Current?

AC stands for Alternating Current. The type of electric current whose magnitude changes continuously and direction changes periodically is known as alternating current or AC. In practice, the alternating current is produced by alternating voltage source such as alternator or AC generator, etc.

The waveform of alternating current (AC) is shown in Figure-1. In case of AC, the total amount of time taken by a waveform of alternating current to itself is known as time period of the AC waveform. The rate at which the waveform repeats itself, i.e. the number of cycle complete in one second, is known as frequency of the AC waveform. The relation between frequency and time period of an AC waveform is given by the following expression.

$$f=\frac{1}{T}$$

There are different types of AC waveforms like sinusoidal AC, square wave, triangular wave, etc. The AC is widely used in our day to day life such as to run fan, bulb, AC, washing machine, etc.

What is Direct Current?

DC stands for Direct Current. The type of electric current whose magnitude does not change with the time and flows only in one direction (i.e. has unidirectional flow) is known as direct current or DC. Therefore, DC has a constant magnitude and direction. Consequently, the frequency of DC is zero.

The waveform of the DC is shown in Figure-2. The DC is widely used in electronic device such as computers, mobiles, laptops, toys, etc. The DC is obtained from battery, cell, DC generators and rectifiers (by converting AC into DC).

Difference between AC and DC

The following table highlights the key differences between alternating current and direct current −

Parameter	Alternating Current (AC)	Direct Current (DC)
Definition	The type of electric current in whose magnitude changes continuously and direction changes periodically is known as alternating current (AC).	The types of electric current whose magnitude and direction does not change with time is known as direct current (DC).
Direction of flow of charge (electrons)	In case of alternating current, the flow of electrons is bidirectional, i.e. electrons flow in both forward and backward direction.	In case of direct current, flow of electrons takes place in only forward direction. Thus, the flow of electrons is unidirectional.
Types	Alternating current may be of various types based on the waveform such as sinusoidal, triangular, square, trapezoidal, etc.	Generally, the direct current is of two types: constant DC and pulsating DC.
Frequency	AC has a specific frequency. In practice, the frequency of AC is 50 Hz or 60 Hz.	The frequency of DC is zero.
Magnitude	The magnitude of alternating current changes continuously.	The direct current has a constant magnitude, i.e. it does not change with time.
Direct of current & polarity	The alternating current flows in both directions (forward and reverse), thus polarity cannot be mentioned in the circuit.	The direct current always flows from positive to negative. Hence, polarity marking is possible in case of DC.
Types of loads	For alternating current, there are three types of loads, i.e. resistive load, inductive load and capacitive load.	DC load includes only resistive load.
Opposition to current flow	The opposition to flow of alternating current offered by the circuit is called impedance.	For DC, the opposition offered by the circuit is termed as resistance.
Source	AC is obtained from AC generators or alternators.	The sources of DC are DC generators, battery, solar cell, etc.
Transmission	AC can be transmitted over long distances with a few losses.	The transmission of DC is more efficient than AC and it can be transmitted over long distances with negligible losses.
Use of Transformer	With AC, a transformer can be used for increasing and decreasing the voltage levels.	With DC, transformer does not work.
Power factor	Power factor of a circuit with AC lies between 0 and 1.	The power factor of circuit with DC always remains unity, i.e. 1.
Applications	AC is used to operate domestic & commercial appliances like fan, light, fridge, etc. and industrial loads like induction motors, etc.	DC is used in laptops, mobiles, electronics devices, toys, industrial processes like electrolysis, etc.

Conclusion

There are various differences between alternating current and direct current as described in the above table. These differences provide the information about the technical parameters of AC and DC. Both these types of electric currents are used in different applications.