Direct current refers to unidirectional current, whereas alternating current refers to current that reverses its direction periodically. Alternating currents are crucial for electricity transmission and distribution. Power supplies in homes use sinusoidal sources to provide electricity. These sources generate a voltage that varies sinusoidally with time. Mathematically, it is represented by a harmonic function, known as a sinusoid, that is defined by its amplitude, angular frequency, and phase. The variation of the function repeats every T seconds, and the duration of one complete cycle is called the period. It is related to the angular frequency. The number of cycles per second is the frequency. Consider two sinusoids with the same frequency. If a sinusoid reaches its maxima and minima earlier than another, then the first sinusoid leads the second. The two sinusoids are then said to be out of phase, and the shift between them is known as the phase difference. If the two sinusoids reach their maxima and minima simultaneously, they are in phase and so have zero phase difference.