What are the similarities and differences between direct current and alternating current?

Answer 1

Both alternating current (AC) and direct current (DC) describe the nature of the current in terms of its direction. DC describes when the flow of electric charge goes in a constant direction whereas AC describes when the flow of electric charge constantly reverses; in other words, the electrodes of the power source constantly switch between positive and negative.

Answer 2

They are both descriptions of the movement of electrons in a conductor.

The differences between ac and dc currents are more interesting to describe!

For more information please see the answer to the Related Question shown below.

Answer 3

In metal conductors, both d.c. and a.c. current consist of rapid, chaotic, movement of free electrons. In a d.c. current, there is a tendency for individual electrons to move towards one end of the conductor (probably in millimetres per hour). In an a.c. current, there is a tendency for individual electrons to match the direction of the alternating voltage applied to the conductor.

Although, in both cases, the effect of the current is more-or-less instant along the entire conductor, the actual movement of individual electrons in either direction is very, very, slow, in comparison to their chaotic and random motion.