G5C01: Transformer: What causes a voltage to appear across

Q: What causes a voltage to appear across the secondary winding of a transformer when an AC voltage source is connected across its primary winding?

The correct answer is C: Mutual inductance. The correct answer is C: Mutual inductance. What causes a voltage to appear across the secondary winding of a transformer when an AC voltage source is connected across its primary winding is mutual inductance. The changing magnetic field from the primary induces voltage in the secondary through mutual inductance. For amateur radio operators, this is how transformers work. Understanding this helps when using transformers.

Updated: Dec 9, 2025 | Source: 2023-2027 Question Pool | Topic: G5C

G5C01G5C

What causes a voltage to appear across the secondary winding of a transformer when an AC voltage source is connected across its primary winding?

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Deep Dive: G5C01

The correct answer is C: Mutual inductance. What causes a voltage to appear across the secondary winding of a transformer when an AC voltage source is connected across its primary winding is mutual inductance. The changing magnetic field from the primary induces voltage in the secondary through mutual inductance. For amateur radio operators, this is how transformers work. Understanding this helps when using transformers.

Why Other Answers Are Wrong

Option A (Capacitive coupling): Incorrect. Transformers don't work through capacitive coupling - they work through magnetic coupling (mutual inductance). Capacitive coupling is different. Option B (Displacement current coupling): Incorrect. Transformers don't work through displacement current - they work through mutual inductance. Displacement current is a different concept. Option D (Mutual capacitance): Incorrect. Transformers don't work through mutual capacitance - they work through mutual inductance. Mutual capacitance is different.

Exam Tip

Transformer voltage transfer = mutual inductance. Think 'T'ransformer = 'T'ransfers through 'M'utual 'I'nductance. Changing magnetic field from primary induces voltage in secondary through mutual inductance. Not capacitive coupling, not displacement current, not mutual capacitance - just mutual inductance.

Memory Aid

Real-World Example

You connect AC voltage to a transformer's primary winding. The changing current creates a changing magnetic field. This magnetic field links to the secondary winding through mutual inductance, inducing voltage in the secondary. This is how transformers transfer energy - through mutual inductance, not through direct electrical connection.

Source & Coverage

Question Pool: 2023-2027 Question Pool

Subelement: G5C

Reference: 2023-2027 Question Pool · G5 - Electrical Principles

Key Concepts

Transformer Mutual inductance Primary and secondary Magnetic coupling

Verified Content

Question from the official FCC General Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the G5C topic.