Question

Fig. shows the current flowing in the coil of wire wound around the soft iron horse shoe core. State the polarities developed at the ends A and B.

• A. At A west and at B east
• B. At A east and at B west
• C. At A north and at B south
• D. At A south and at B north

Answer 1

Answer: (D)

At A south and at B north

Consider a coil of wire wound around an iron core that is in the shape of a horse shoe. When connected to a current source, the coil becomes energized, creating a magnetic field just like a permanent magnet. The magnetic flux density is proportional to the magnitude of the current flowing in the wire of the electromagnet.
The polarity of the electromagnet is determined by the direction the current. The north pole of the electromagnet is determined by using our right hand. If we wrap our fingers around the coil in the same direction as the current is flowing (conventional current flows from + to -). The direction our thumb is pointing is the direction of the magnetic field, so north would come out of the electromagnet in the direction of our thumb. Hence, in the polarity at A would be south pole and the polarity at B would be north pole.
Below is the diagram of an electromagnet with the polarities marked.