Induced Magnetism in Ferromagnetic Materials

Steps:

• Identify induced magnetism as temporary magnetization of a ferromagnetic material in an external magnetic field.
• Examine each diagram for presence of an external magnetic field near the nail without permanent magnetization.
• Rule out situations with no field, permanent magnets, or self-generated fields.
• Select the diagram showing the nail solely in an external field from a nearby permanent magnet.

Why A is correct:

• Diagram A places the nail near a bar magnet, inducing temporary north and south poles per the law of magnetic induction in ferromagnets.

Why the others are wrong:

• B: No external magnetic field; nail is unmagnetized.
• C: Nail is a permanent magnet itself, not induced.
• D: Nail forms an electromagnet via current, self-magnetizing rather than induced by external field.

Final answer: A