Q. Which of the following have a significant influence on a material’s electrical resistivity?
1. Shape of the conductor
2. Size of the conductor
3. Nature and temperature of the conductor
4. All of the above
Answer: 3 (Nature and temperature of the conductor).
Explanation: The material’s electrical resistivity is highly dependent on its nature and temperature, but not on its size and shape. The materials or substances that show less resistivity are called good conductors, while the substances that have higher resistivity are called bad conductors or insulators. The resistivity of semi-conductors falls between the resistivity of good conductors and nonconductors (insulators).
Examples: The metals are the best examples of good conductors. Crystalline solids are the most common semiconducting materials. While the materials made by ceramics are insulators.
Metals example: Aluminium, Copper, Gold, Iron, Mercury, Silver, etc.
Crystalline solids example: Amethyst, Agate, Citrine, Diamond, Quartz, Rose quartz, etc.
Insulators example: Glass, Plastic, Paper, Rubber, Styrofoam, Wood, etc.
Note: The resistivity of semiconductors falls as their temperature increases. So, more conductivity of semiconductors can be noticed at their highest temperature. Moreover, the metals (good conductors) behave oppositely (if their temperature increases then the conductivity decreases).
Key point: Electrical conductivity of the earth is influenced by its metal content especially the sulfides in the rock material.
Other important questions:
Q. The alpha-helix and beta-sheet are found at which level of protein organization?
Q. Which cytoskeletal proteins provide the structural support for microvilli?
Q. Which of these does not contain a structural protein?
Q. What level of protein structure is associated with the sequence of amino acids?
Q. Which of the following pertains to typhoid fever?
Q. Which of the following tests is an agglutination test for the bacterium causing typhoid fever?
Q. This is a compound made from a group of covalently bonded atoms?
Q. If two covalently bonded atoms are identical the bond is ?
Q. Which of the following are characteristics of G protein-coupled receptors (GPCR)?
Q. What are the second messengers in the GPCR-phospholipase c signal transduction system?
