Why is the primary winding wire of a voltage step-up transformer usually a larger size than that of the secondary winding?
The correct answer is B: To accommodate the higher current of the primary. Why the primary winding wire of a voltage step-up transformer is usually larger than that of the secondary is to accommodate the higher current of the primary. In a step-up transformer, primary voltage is lower but current is higher, requiring larger wire. For amateur radio operators, this explains transformer wire sizing. Understanding this helps when designing transformers.
Exam Tip
Step-up transformer primary wire larger = accommodate higher current. Think 'S'tep-up 'P'rimary = 'S'maller 'P'ower (voltage) but 'H'igher 'C'urrent. Primary has lower voltage but higher current, requiring larger wire. Not coupling, not oscillations, not volume - just current capacity.
Memory Aid
"Step-up transformer primary wire larger = accommodate higher current. Think 'S'tep-up 'P'rimary = 'H'igher 'C'urrent. Primary has lower voltage but higher current, requiring larger wire. Wire size determined by current."
Real-World Application
A step-up transformer: 120V primary, 480V secondary (4:1 step-up). Primary current is 4× secondary current (power is same). The primary wire must be larger to handle the higher current, even though voltage is lower. Wire size is determined by current, not voltage.
Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. Larger wire doesn't improve coupling - coupling depends on core design and winding technique, not wire size. Coupling isn't the reason.
Option C: Incorrect. Larger wire doesn't prevent parasitic oscillations - oscillations come from circuit design, not wire size. Oscillations aren't the reason.
Option D: Incorrect. Wire volume equality isn't the reason - wire size is determined by current, not volume. Volume isn't the consideration.
题目解析
The correct answer is B: To accommodate the higher current of the primary. Why the primary winding wire of a voltage step-up transformer is usually larger than that of the secondary is to accommodate the higher current of the primary. In a step-up transformer, primary voltage is lower but current is higher, requiring larger wire. For amateur radio operators, this explains transformer wire sizing. Understanding this helps when designing transformers.
考试技巧
Step-up transformer primary wire larger = accommodate higher current. Think 'S'tep-up 'P'rimary = 'S'maller 'P'ower (voltage) but 'H'igher 'C'urrent. Primary has lower voltage but higher current, requiring larger wire. Not coupling, not oscillations, not volume - just current capacity.
记忆口诀
Step-up transformer primary wire larger = accommodate higher current. Think 'S'tep-up 'P'rimary = 'H'igher 'C'urrent. Primary has lower voltage but higher current, requiring larger wire. Wire size determined by current.
实际应用示例
A step-up transformer: 120V primary, 480V secondary (4:1 step-up). Primary current is 4× secondary current (power is same). The primary wire must be larger to handle the higher current, even though voltage is lower. Wire size is determined by current, not voltage.
错误选项分析
Option A: Incorrect. Larger wire doesn't improve coupling - coupling depends on core design and winding technique, not wire size. Coupling isn't the reason. Option C: Incorrect. Larger wire doesn't prevent parasitic oscillations - oscillations come from circuit design, not wire size. Oscillations aren't the reason. Option D: Incorrect. Wire volume equality isn't the reason - wire size is determined by current, not volume. Volume isn't the consideration.
知识点
Step-up transformer, Primary winding, Larger wire, Higher current
Verified Content
Question from official FCC General Class question pool. Explanation reviewed by licensed amateur radio operators.