Which is true? An ideal emf device has internal resistance and a real emf device does not. A real emf device sets up a potential difference and an ideal emf device does not. An ideal emf device sets up a potential difference and a real emf device does not. A real emf device has internal resistance and an ideal emf device does not.

A real emf device has internal resistance and an ideal emf device does not

Explanation:

What is EMF?

The electromotive force or potential difference or voltage is the reason behind the flow of current in a circuit.

What is Ideal emf device?

The ideal emf device is one which doesn't have any internal resistance and it provides a fixed emf regardless of the load current.

What is Real emf device?

But nothing is ideal in real world, A real emf device would have some internal resistance in series with the emf device.

Conclusion:

The internal resistance causes voltage drop therefore, as the load current changes, the voltage drop changes and hence device emf changes.