Introduction:
When a conductor rotates in a bipolar magnetic field, an electromotive force (emf) is induced in the conductor. The emf induced in the conductor can be either DC (direct current) or AC (alternating current) depending on certain factors.

Explanation:
The emf induced in a conductor rotating in a bipolar field can be understood by Faraday's law of electromagnetic induction. According to Faraday's law, the emf induced in a conductor is directly proportional to the rate of change of magnetic flux through the conductor. The magnetic flux can be defined as the product of the magnetic field strength and the area enclosed by the conductor.

DC Induced Emf:
When a conductor rotates in a bipolar field at a constant speed, the rate of change of magnetic flux through the conductor remains constant. In this case, the emf induced in the conductor is a DC emf. This is because the rate of change of magnetic flux is constant, resulting in a constant magnitude and direction of the induced emf.

AC Induced Emf:
If the rotational speed of the conductor changes or the strength of the magnetic field changes, the rate of change of magnetic flux through the conductor varies. In this case, the emf induced in the conductor is an AC emf. The magnitude and direction of the emf change periodically, resulting in an alternating current.

Conclusion:
In summary, the emf induced in a conductor rotating in a bipolar field can be either DC or AC. If the conductor rotates at a constant speed and the magnetic field strength remains constant, the induced emf is DC. However, if there is a variation in the rotational speed or the magnetic field strength, the induced emf is AC. Therefore, the correct answer to the question is option 'C' - AC only.