Turn counting: A transformer has 400 primary turns and 2,000 secondary turns. What is the turns ratio Np:Ns (expressed as a number Np/Ns)?
Electronics
Transformers
Difficulty: Easy
Choose an option
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A0.4
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B0.2
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C5
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D25
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E2
Answer
Correct Answer: 0.2
Explanation
Introduction / Context:Accurately computing the turns ratio is foundational for predicting output voltage and reflected impedances. This problem reinforces the simple division that defines Np/Ns in a transformer.
Given Data / Assumptions:
- Np = 400 turns.
- Ns = 2,000 turns.
- Ideal transformer conventions.
Concept / Approach:The turns ratio expressed as a single number is Np/Ns. Use direct division of the primary turns by the secondary turns.
Step-by-Step Solution:
Compute r = Np/Ns = 400 / 2000.400 / 2000 = 0.2.Therefore, the turns ratio (as a number) is 0.2.Verification / Alternative check:As a colon ratio, this is 1:5 (since 0.2 = 1/5). That means the transformer is step-up by 5 in voltage when driven on the primary.
Why Other Options Are Wrong:
- 0.4: Would correspond to 400/1000, not the given turns.
- 5 or 25: Those are Ns/Np magnitudes or unrelated; the question asks Np/Ns.
- 2: Not supported by the given turn counts.
Common Pitfalls:
- Accidentally computing Ns/Np instead of Np/Ns.
- Forgetting to simplify the fraction correctly.
Final Answer:0.2