An ideal transformer has a turns ratio of 5 (primary to secondary). If 120 V AC is applied to the primary, what is the expected secondary voltage, assuming the usual ratio definition?

Introduction / Context:
Transformers scale voltage and current according to their turns ratio. Correctly interpreting a stated turns ratio is essential for predicting secondary voltage in power and signal applications.

Given Data / Assumptions:

• Turns ratio = 5, interpreted as N_primary : N_secondary = 5 : 1, the common convention unless otherwise specified.
• Applied primary voltage Vp = 120 V AC.
• Ideal transformer with negligible losses and no load effects.

Concept / Approach:
For an ideal transformer, Vp / Vs = Np / Ns. With Np / Ns = 5, Vs = Vp / 5. Therefore, Vs = 120 / 5 = 24 V. This corresponds to a step-down transformer by a factor of 5.

Step-by-Step Solution:
Step 1: Use Vp / Vs = Np / Ns.Step 2: Substitute Np / Ns = 5 and Vp = 120 V.Step 3: Compute Vs = 120 / 5 = 24 V.

Verification / Alternative check:
If the ratio were given as secondary to primary instead, the result would be 600 V; however, the industry default is primary to secondary unless stated otherwise. The option 24 V matches the usual interpretation.

Why Other Options Are Wrong:

• 4.73 and 0.4 V: Not consistent with any reasonable interpretation of a turns ratio of 5 with 120 V primary.
• 600 V: Would require a 1:5 step-up ratio, not the standard reading of 5 as primary to secondary.
• None of the above: Incorrect because 24 V is correct.

Common Pitfalls:
Confusing the order of the ratio. Always verify whether the ratio is primary to secondary or secondary to primary before calculating voltages.

Final Answer:
24 V.