State the difference between generator and alternator?

Generator and alternator are two devices, which converts mechanical energy into electrical energy.
Both have the same principle of electromagnetic induction, the only difference is that their construction.
Generator persists stationary magnetic field and rotating conductor which rolls on the armature with slip rings and brushes riding against each other, hence it converts the induced emf into dc current for external load whereas an alternator has a stationary armature and rotating magnetic field for high voltages but for low voltage output rotating armature and stationary magnetic field is used

In Generator Filed is stationary(Permanent Magentic Poles) & Armature is rotating.So at synchronous rpm, according to Pole Frequency is set & Alternating Voltage is produced in Rotating Armature. By the use og Commutator brushes/ Rotating Diode we convert ac in dc.

But in case of Alternator it is just opposite i.e DC field is rotating & Armature is stationary.At synchoronous rpm Rotor( roting field) emf will cut the statot(armature) conductor & emf is produced.

Interestingly Both will convert mechanical rotation in Electrical Energy. 

Generator, The name itself indicates that it generates something. But here the generator generates electricity by conerting the mechanical energy into electrical energy. The generated energy may be Direct Current(DC) or Alternating Current(AC).

 

But Alternator is the device which generates only Alternating Current(AC).

 

The construction of DC generator and Alternator varies only at the receiving end. i.e the DC generator consists of commutator(rotary converter) at the end, which converts the alternating voltage into direct voltage(uni directional). But the Alternator consists of slip rings at the end which just receives the generated voltage(Bi-Directional).

 

 

Generator May Produce DC or AC Power.

 

Alternator, Produces only AC Power.

 

Further, Intially it used to be Enginator (Engine + Alternator); which with the time passage becomes Generator.

simply generator contain dc voltage and alternator contain Ac voltage.
that is the basic difference in both devices

Generator is having Permanent magnet while alternator is having Dc field. 

Alternator  is the one  which produces alternating frequency   .Generator  is  (Alternator+ Engine) .