Question 36

The Correct Answer is B **Explanation for B (electromagnet):** An electromagnet is a temporary magnet created when electric current flows through a wire. Specifically, a device consisting of a wire coiled around a soft iron core (or other ferromagnetic material) becomes magnetic when a direct current (DC) passes through the coil. This process concentrates the magnetic field produced by the current, making the iron core highly magnetic. This description perfectly matches the definition and construction of an electromagnet. **Explanation for Incorrect Options:** * **A) piezoelectric device:** A piezoelectric device uses materials that generate an electric charge when mechanically stressed, or conversely, undergo a mechanical change when an electric field is applied. This principle is entirely different from using current to magnetize an iron core. * **C) electromagnetic domain:** An electromagnetic domain (or simply magnetic domain) refers to small regions within ferromagnetic materials (like the soft iron core itself) where the magnetic moments of the atoms are aligned. It describes a microscopic internal structure of the material, not the entire constructed device powered by electricity. * **D) magnetic shield:** A magnetic shield is a device or enclosure made of a high-permeability material used to block or redirect external static or low-frequency magnetic fields away from sensitive equipment. It is designed to *prevent* magnetism from affecting an area, not to *create* a controllable magnet.