. Both AC (Alternating Current) and DC(Direct Current) describe types of current flow in a circuit.
 . DC: Charge flows only in one direction.
 . AC: Changes direction of flow periodically.

How is electric current produced?

 . By moving a metal wire through magnetic field.
 . Electric generator rotates a coil of wire through magnetic field.
 . The produced current is AC.
 Slip rings transfer power across rotating structure.
 . Carbon brush conducts current between stationary wires and rotatory wires.
 . It produces sinusoidal, triangular or square wave. Mostly sine wave is prefered for easy calculations.
 . Can easily convert into different voltages using transformer.
 . To produce DC current there are many methods: 
    - Chemical reactions in Batteries
    - Using Rectifiers to convert AC current into DC current
    - Using ring commutators in the circuit to automatically change rotation of current produced.

Usage of AC and DC:

 . AC current is mostly preferred to supply electricity over longer distances.
 . AC is easily stepped up and down with the help of transformers.
 . While sending to longer distances, voltage is stepped up and sent.Power loss will be minimum.
 . If DC is used instead, transformers won't work.
 . DC-DC voltage converters can be used but they are very complex.
 . So, it is not suitable for longer distance transmissions because power is lost.
 . DC is used in most of electronic appliances which run on IC's and other elements which require constant voltage.
 . In this case, AC is not suitable because voltage goes on varying.

Differences between AC and DC:

Transferring EnergySafer to transfer over longer distances and provide more power.Cannot travel over longer distances. Loses power.
DirectionEnergy constantly changes directionFlows in one direction
CurrentMagnitude varies with timeMagnitude is constant
Cause of current flowRotating magnets along wireSteady magnetism
Obtained from:AC Generators, mainsBatteries, cells
Frequency50Hz or 60Hz0
TypesSine, triangular, squarePure and Pulsating
Power FactorLies between 0-1Always 1
UsageHome, Office supplyMost of electronic devices
ConversionUse Rectifiers to convert AC to DCUse Inverters to convert DC to AC
SafetyAC is safer since voltage comes to equilibrium at timesVoltage is constant, not much safer.