What is Electricity? What is meant by DC and AC Current ?

Electricity:

Electricity is the flow of electrons from one atom to another in a conductor. If there are excess electrons at one end of the conductor, these will be attracted towards the protons of the atoms present in a conductor. This will create a push force for the electrons towards the protons. This push force is dependent upon the number of electrons that are attracted to the protons. This force is called Electromotive Force (EMF).

EMF is defined as a force that expels the electron out of its orbit and towards the excess protons. The removal of electron from the atom will cause him acquire a positive charge because the number of protons will increase, this atom will in return attract the electrons of the neighboring atoms. Thus a chain reaction will be started as one atom gains an electron and other releases an electron. There will be a flow of free electrons that is known as electricity.

Direct Current (DC):

In Direct Current the flow of electricity is in a same direction. Direct Current is produced by batteries and solar cells and some commutator-type electric generators. Direct Current is applicable to low voltage applications that are powered by batteries or solar power systems.
Battery is an example of direct current source. It can be seen that batteries have positive (+) and negative (-) terminals. When some device is attached between the two terminals of the battery electricity starts flowing in one direction and causes the device to work. Through a wire than it receives electric current and functions. This phenomenon can be validated by connecting a small light bulb between the terminals of a battery. The light will start glowing as the electrons pass through the bulb filament.
Direct Current is used to power portable devices, such devices usually run on batteries. That electric wiring in houses is AC power and it is completely different than DC. Direct Current can also be obtained by using rectifier to convert Alternating Current to Direct Current.

Alternating Current (AC):

Alternating Current is a type of current whose direction of flow is periodically reversed. Alternating Current is produced by power plants to deliver electricity to business firms and residences. The Alternating Current is mostly a sinusoidal form of electricity but it can be triangular or square wave. The number of times in which the direction of AC Voltage is changed is known as frequency of AC Current. Commercially the frequency of AC is 50 Hz.

AC power is used all over the world for power generation and transmission. The devices required to produce AC are less expensive and are easier to make. For transmission of power it is essential to increase and decrease the current and for AC generation devices it is easier and cheaper. The power switches for AC power are also less expensive to manufacture. The major advantage of AC in transmission of power is that high voltages can be used with small currents to reduce losses. Power can be transmitted using DC but the losses would be huge.