Transformer basics — turns ratio check: A transformer has 700 turns on the primary winding and 35 turns on the secondary winding. Determine whether the stated turns ratio of 20:1 (primary:secondary) is correct, based on the definition turns ratio = Np:Ns.

Introduction / Context:
Transformers are characterized by their turns ratio, defined as the number of primary turns to the number of secondary turns. This ratio directly sets the ideal voltage ratio and relates to the current ratio inversely. The question asks you to verify whether a primary of 700 turns and a secondary of 35 turns corresponds to a 20:1 turns ratio.

Given Data / Assumptions:

• Primary turns Np = 700.
• Secondary turns Ns = 35.
• Standard definition of turns ratio: a = Np:Ns.
• Assume conventional winding definitions; no need for frequency or load to compute the ratio.

Concept / Approach:
The turns ratio is purely a geometric/winding count relationship. For ideal transformers, Vp/Vs = Np/Ns and Is/Ip = Np/Ns. Determining the turns ratio requires only the turn counts, not operating conditions.

Step-by-Step Solution:

Verification / Alternative check:
If the transformer is ideal, a = Vp/Vs. A 20:1 turns ratio would step 120 V to 6 V, or 240 V to 12 V, which are common secondary voltages, supporting the plausibility of the computed ratio.

Why Other Options Are Wrong:
Incorrect: The arithmetic clearly shows 700:35 reduces to 20:1.

Correct only for ideal transformers: The turns ratio itself is independent of ideality; ideality affects voltage regulation and losses, not the count ratio.

Indeterminate without frequency: Frequency does not change the turns ratio calculation.

Common Pitfalls:
Confusing turns ratio with impedance ratio (which is the square of the turns ratio). Mixing up primary and secondary order when expressing the ratio.

Final Answer:
Correct