The question asks to identify a good conductor of electricity among the given options. To answer this, we need to understand the basic properties of electrical conductors and insulators.
Correct Option: B) Copper is a metal and possesses a large number of free electrons, which are essential for conducting electricity. This makes it an excellent conductor, commonly used in electrical wiring and components.
The fundamental difference between conductors and insulators lies in their ability to conduct electricity. This ability is directly related to the presence or absence of free charge carriers, primarily electrons, within their atomic structure.
A) Conductors have free electrons; insulators do not. This statement accurately describes the main difference. Conductors possess a significant number of free electrons that can move and carry electric current, whereas insulators have very few or no free electrons, making them poor conductors.
The question asks about the energy gap between the conduction band and the valence band in a good conductor. This concept is fundamental to understanding the electrical properties of materials, specifically how they conduct electricity.
D) Zero. In good conductors, the valence band and conduction band either overlap or are contiguous, meaning there is no energy gap. Electrons can move freely into the conduction band, enabling high electrical conductivity.
The question asks to identify an insulator from the given options. An insulator is a material that does not allow electricity or heat to pass through it easily. This property is due to the absence of free electrons that can move and carry charge or thermal energy.
Correct Option: C) Rubber
The question asks how the resistivity of a conductor changes with temperature and pressure. We need to recall the fundamental principles of electrical conductivity in materials, specifically how temperature affects the movement of charge carriers (electrons) and their collisions within the conductor.
B) Increase in temperature — As explained above, higher temperatures lead to increased atomic vibrations, causing more frequent collisions with free electrons, thereby increasing the resistivity of the conductor.
The question asks about the fundamental property of a semiconductor, specifically concerning its energy band structure. To answer this, we need to recall the definitions of valence band and conduction band and how they are populated in semiconductors compared to conductors and insulators.
Correct Option: A) It has an almost empty conduction band and an almost filled valence band.
This statement accurately describes the state of a semiconductor at temperatures above absolute zero (e.g., room temperature), where it exhibits its characteristic semiconducting properties. At absolute zero, the conduction band would be completely empty and the valence band completely filled. However, the term "almost" accounts for the thermal excitation of electrons at practical temperatures, which is what gives semiconductors their utility.