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)?

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:

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