Which of the following is a good electrical insulator?
The correct answer is B: Glass. Glass is a good electrical insulator because it has very few free electrons and very high resistance, preventing current flow. Insulators are materials that oppose electrical current flow.
Glass is made of silicon dioxide and other compounds that have tightly bound electrons. These electrons are not free to move, so glass has very high electrical resistance. This makes glass an excellent insulator - it prevents electrical current from flowing through it. Glass is commonly used as an insulator in electrical equipment, such as insulating supports, insulators on power lines, and insulating materials in electronic components. Good insulators have high resistance and few free electrons, opposite of good conductors.
Exam Tip
Good insulator = Glass. Remember: Glass is a good electrical insulator because it has very high resistance and few free electrons, preventing current flow.
Memory Aid
"**G**ood **I**nsulator = **G**lass (think 'GI = G' = Good Insulator = Glass)"
Real-World Application
Power line insulators are made of glass or ceramic because these materials are excellent insulators. They prevent electrical current from flowing from the high-voltage power line to the support structure. Glass's high resistance and lack of free electrons make it safe to use as an insulator, preventing dangerous electrical current flow.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. Copper is an excellent conductor, not an insulator. It has many free electrons and low resistance.
Option C: Incorrect. Aluminum is a good conductor, not an insulator. It's commonly used for electrical wiring.
Option D: Incorrect. Mercury is a liquid metal and a good conductor, not an insulator.
题目解析
The correct answer is B: Glass. Glass is a good electrical insulator because it has very few free electrons and very high resistance, preventing current flow. Insulators are materials that oppose electrical current flow. Glass is made of silicon dioxide and other compounds that have tightly bound electrons. These electrons are not free to move, so glass has very high electrical resistance. This makes glass an excellent insulator - it prevents electrical current from flowing through it. Glass is commonly used as an insulator in electrical equipment, such as insulating supports, insulators on power lines, and insulating materials in electronic components. Good insulators have high resistance and few free electrons, opposite of good conductors.
考试技巧
Good insulator = Glass. Remember: Glass is a good electrical insulator because it has very high resistance and few free electrons, preventing current flow.
记忆口诀
**G**ood **I**nsulator = **G**lass (think 'GI = G' = Good Insulator = Glass)
实际应用示例
Power line insulators are made of glass or ceramic because these materials are excellent insulators. They prevent electrical current from flowing from the high-voltage power line to the support structure. Glass's high resistance and lack of free electrons make it safe to use as an insulator, preventing dangerous electrical current flow.
错误选项分析
Option A: Incorrect. Copper is an excellent conductor, not an insulator. It has many free electrons and low resistance. Option C: Incorrect. Aluminum is a good conductor, not an insulator. It's commonly used for electrical wiring. Option D: Incorrect. Mercury is a liquid metal and a good conductor, not an insulator.
知识点
Insulators, Glass, Electrical resistance, Electrical safety
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.