# Basic idea of AC and DC

Alternating Current: AC means alternating current. The electric current which repeats its flowing direction periodically is called alternating current. This theme can be competent for AC voltage also. A very simple example of AC signal is sinusoidal wave. A sinusoidal wave obeys the function y = sinx in every instant of time, where x=time and y = amplitude of wave. Get idea about it from the figure given below. Amplitude: The maximum value either positive or negative of an AC signal is called amplitude. In above figure the maximum value of signal is denoted by Im and it is equal to 5V and in negative is –5V.

Frequency: The number of cycle completed in 1 second is called the frequency of AC signal. Its unit is cycle/second or Hz. If 1 cycle takes T time to complete the frequency is f = 1/T.

Period: Required time to complete 1 cycle is called period. It is denoted by T and T=1/f.

Cycle: Cycle is the travelling path of wave from a specific point to next same point on wave between two risings or falls or peaks. AC Sources: Alternator, Oscillator etc.

Symbol: Symbol of AC voltage source is drawn below. This symbol is used frequently in most electronic schematic diagram. Characteristics:

(i) AC has some amount of frequency.
(ii) Constant maximum amplitude level.
(iii) AC has different maximum value and root mean square value of amplitude.

Direct Current: DC means direct current. The unidirectional electric current which continues its flow with a certain level of amplitude with respect to time is called direct current. This theme can be competent for DC voltage also. Although the term DC stands for direct current, DC often used to refer constant polarity of current or voltage. Get idea about it from the figure given below. DC Sources: Popular DC sources are Dynamo, Battery and Regulated Power Supply etc. Dynamo can generate DC voltage and can supply DC to load. Battery is the storage medium of DC voltage and can give high current. Regulate power supply is a DC source which converts AC mains to regulated DC to operate DC loads.

Symbol: Symbols of DC voltage source is drawn below. These symbols are used frequently in most electronic schematic diagram. Characteristics:

(i) DC has constant zero frequency.
(ii) It has constant amplitude level.
(iii) Pure DC has no different root mean square value but amplitude.