Nature of induced emf in Faraday's law When there is a battery in a simple circuit loop, for instance, there is a real low potential terminal and a high potential terminal , the battery does work on charges and delivers them at high potential on another end from where the charges lose potential as they come back to the other terminal , however I cannot see such 'terminals' so to speak or rather points across which there is a potential difference in a closed loop having a bulb through which magnetic field is being changed, where is the potential difference being applied then, wherever I see the loop I cannot see a difference, same current, same resistance of dl length of loop, still current is cycling through it.
Or is it that the source of movement is no electrostatic in nature, what exactly is the nature of mechanism which produces this current?
 A: You are right: the source of movement is not electrostatic in nature. Around the changing magnetic field there curls an electric field. This electric field does not arise from quasi-static charges, is not computable from Coulomb's law and cannot have the concept of potential difference applied to it. 
But the electric field around a changing magnetic field is a proper electric field nonetheless, because it exerts a force on charges, even if these are stationary. So if you have a loop of wire through which the magnetic flux is changing, the free electrons in the wire will be urged around the loop. The emf is the work done per unit charge on any charge going once round the loop. [We cam still talk about the emf round a closed path, even if there is no conducting material around that path.]
You might now be tempted to ask, "What causes an electric field to curl around a changing magnetic field?" It's not really a case of cause and effect: it's better to think of the electric field and the changing magnetic field as parts of one electromagnetic field, inseparably associated at each point by the Maxwell equation 
$$\vec{\text{curl}} \vec E=-\frac{d \vec B}{dt}.$$
