Interpoles in a dc motor must be

1. series excited and should have polarity opposite to that of the next main pole in the direction of rotation of armature.
2. series excited had should have the same polarity as that of the next main pole in the direction of rotation of the armature.
3. shunt excited and should have polarity opposite to that of the next main pole in the direction of rotation of the armature.
4. shunt excited and should have t he same polarity as the next main pole in the direction of rotation of the armature.