Question

explain non-conservative field EMF

Answer 1

By definition a conservative field is irrotational which means if you perform a path integral around a closed loop, the result is zero. This is also the condition for a potential function describing the field to exist.

In terms of the static electric field set up by stationary charges, it is conservative because if you start at point A in space and perform some complicated walkabout, then arrive back at A, the amount of work you did is zero. The integral around a closed loop of E dot dL is zero. This allows a scalar potential function to be found for E, called the voltage that can completely describe the E field at every point.

The non-conservative E field is generated by something that violates the property that integral around a closed path of E dot dL = 0. A changing magnetic field can create an emf around a closed loop, as described by Faraday's Law or mathematically with one of Maxwell's equations: curl E = - dB/dt. Stokes's theorem says this is equivalent to integral around a closed path of E dot dL = -d phi/dt where phi is the flux passing through a surface connected to that closed loop. That is by definition a non-conservative E field.