12. Differentiate between direct current (DC) and alternating current (AC). Define the following terms for AC: (i) Cycle, (ii) Time period, (iii) Frequency.

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

Terms for AC:

1. Cycle:

   • A cycle is one complete oscillation of the alternating current or voltage. In other words, it refers to the process where the current or voltage goes from its positive peak to zero, then to its negative peak, and back to zero again.
   • For example, if an AC waveform reaches its peak positive value, drops back to zero, reaches the peak negative value, and then returns to zero, that completes one cycle.

2. Time Period:

   • The time period (T) is the time taken to complete one full cycle of the AC waveform. It is measured in seconds (s).
   • The time period tells you how long it takes for the current or voltage to go through one complete cycle. For a sinusoidal AC wave, if the time taken to complete a cycle is 0.01 seconds, the time period is 0.01 seconds.

3. Frequency:

   • The frequency (f) is the number of cycles of the alternating current or voltage that occur in one second. It is measured in hertz (Hz).

   • The frequency is the inverse of the time period. Mathematically:

     f=1/T ​

     Where:

     • $f$ = frequency (in Hz)
     • $T$ = time period (in seconds)

   • For example, if the time period is 0.02 seconds, the frequency will be:

     f=10.0/2=50 Hz

     This means the AC waveform completes 50 cycles per second.

Summary:

• DC (Direct Current): The current flows in one direction only (constant voltage).
• AC (Alternating Current): The current changes direction periodically, forming a sinusoidal waveform.