Faraday’s law application: if the number of turns in a coil placed in a changing magnetic field is decreased, how does the induced voltage change?

Introduction / Context:
Induced voltage in a coil is the foundation of transformer design, sensors, and generators. Faraday’s law explicitly shows how coil geometry (number of turns) and the time rate of change of magnetic flux determine the induced electromotive force (emf). This question checks whether you understand the direct proportionality to turns.

Given Data / Assumptions:

• The coil sits in a time-varying magnetic field.
• Only the number of turns N is changed; the magnetic flux change dΦ/dt remains the same.
• Winding resistance and core effects are ignored for the proportional reasoning.

Concept / Approach:
Faraday’s law states: induced emf E = -N * dΦ/dt. If dΦ/dt is fixed by the external field and motion, E scales linearly with the number of turns N. Therefore, fewer turns yield a smaller induced emf.

Step-by-Step Solution:

Verification / Alternative check:
In a transformer, halving the secondary turns halves the secondary voltage for the same primary flux. Laboratory tests with a signal source driving a core and swapping secondaries of different turns immediately confirm proportionality.

Why Other Options Are Wrong:

• Increase / be excessive: Opposite to the proportional relationship with N.
• Remain constant: Would require N to remain constant or dΦ/dt to change inversely, which is not the case here.
• Become zero: Only true if turns go to zero (no coil) or the field change ceases.

Common Pitfalls:

• Confusing turns with flux; turns scale voltage, not the external field change.
• Ignoring polarity sign; the question asks about magnitude, not direction.

Final Answer:
decrease