In the case of direct current:

Direct Current:

• Direct current (DC) is an electric current that is unidirectional, so the flow of charge is always in the same direction.

• In the direct current (DC), the direction and magnitude of the current do not change. It remains constant with time.
• The positive and negative terminals of a battery are always, respectively, positive and negative.
• Current always flows in the same direction between the terminals. 
• It is used in many household electronics and in all devices that use batteries.
• Examples: Batteries, Fuel cells, solar cells

Direct Current is shown in the figure:

Alternating Current:

• The current that changes its magnitude and polarity at regular intervals of time is called an alternating current.
• The major advantage of using the alternating current instead of direct current is that the alternating current is easily transformed from a higher voltage level to a lower voltage level.
• AC is the most commonly used and most preferred electric power for household equipment, office, and buildings, etc.
• For Alternating current both magnitude and direction change. The frequency of alternating current in Indian power supply is 50 Hz. The time period is 1/50 = 20 m sec.

Alternating Current is shown in the figure

Sinusoidal Current:

• An alternating current that constitutes a sinusoidal function of time in the form I = Im sin (ωt + ϕ)
• The use of sinusoidal currents in technology simplifies electrical devices and circuits, as well as design calculation.