What are the units of electrical resistance?
The correct answer is C: Ohms. The units of electrical resistance are ohms (symbol: Ω). Resistance is the opposition to current flow in a circuit, and the ohm is the standard unit for measuring this opposition.
One ohm is defined as the resistance that allows one ampere of current to flow when one volt is applied. Resistance is a fundamental property of materials - conductors have low resistance (allow current to flow easily), while insulators have very high resistance (oppose current flow). Understanding resistance is crucial for amateur radio, as it affects power delivery, signal loss in feedlines, and antenna matching.
Exam Tip
Resistance = Ohms. Remember: Electrical resistance is measured in ohms (Ω). Resistance opposes current flow.
Memory Aid
"**R**esistance = **O**hms (think 'R = O' = Resistance = Ohms, symbol Ω)"
Real-World Application
Your antenna feedline has a resistance of 0.1 ohms. This low resistance means the feedline doesn't significantly oppose current flow, so most of your transmitter's power reaches the antenna. If the feedline had high resistance (many ohms), it would waste power as heat and reduce the power delivered to your antenna.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. Siemens is the unit of conductance (the inverse of resistance), not resistance itself.
Option B: Incorrect. Mhos is an older term for Siemens (conductance), not the unit of resistance.
Option D: Incorrect. Coulombs measure electric charge, not resistance.
题目解析
The correct answer is C: Ohms. The units of electrical resistance are ohms (symbol: Ω). Resistance is the opposition to current flow in a circuit, and the ohm is the standard unit for measuring this opposition. One ohm is defined as the resistance that allows one ampere of current to flow when one volt is applied. Resistance is a fundamental property of materials - conductors have low resistance (allow current to flow easily), while insulators have very high resistance (oppose current flow). Understanding resistance is crucial for amateur radio, as it affects power delivery, signal loss in feedlines, and antenna matching.
考试技巧
Resistance = Ohms. Remember: Electrical resistance is measured in ohms (Ω). Resistance opposes current flow.
记忆口诀
**R**esistance = **O**hms (think 'R = O' = Resistance = Ohms, symbol Ω)
实际应用示例
Your antenna feedline has a resistance of 0.1 ohms. This low resistance means the feedline doesn't significantly oppose current flow, so most of your transmitter's power reaches the antenna. If the feedline had high resistance (many ohms), it would waste power as heat and reduce the power delivered to your antenna.
错误选项分析
Option A: Incorrect. Siemens is the unit of conductance (the inverse of resistance), not resistance itself. Option B: Incorrect. Mhos is an older term for Siemens (conductance), not the unit of resistance. Option D: Incorrect. Coulombs measure electric charge, not resistance.
知识点
Resistance, Ohms, Electrical units, Opposition to current
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.