Final answer:
The primary difference between a permanent magnet and an electromagnet is that a permanent magnet has a persistent magnetic force, while an electromagnet's magnetic force can be switched on and off. Both types of magnets have poles that interact in the same way: like poles repel and opposite poles attract. Option b is the correct answer.
Step-by-step explanation:
The difference between a permanent magnet and an electromagnet lies in their magnetization and the flexibility of controlling their magnetic fields. A permanent magnet is made from a material that generates its own persistent magnetic field. The magnetism in a permanent magnet arises from the alignment of microscopic magnetic domains within the material. Such a magnet, as its name suggests, has a permanent magnetic force and cannot be easily turned off.
On the other hand, an electromagnet is created by passing an electric current through a coil of wire around a core material that is typically made of iron or another ferromagnetic material. The magnetic field in an electromagnet can be controlled: when the current flows, the electromagnet is 'on' and produces a magnetic field; when the current stops, the magnetic field 'turns off'. Therefore, the magnetic force of an electromagnet can be switched on and off at will.
The interaction between the poles of magnets—whether they are permanent magnets or electromagnets—is consistent: like poles repel and unlike poles attract. This fundamental characteristic of magnetism indicates that the correct answer to the student's question is (b) a permanent magnet always has a magnetic force, but an electromagnet can be switched on and off.