Faraday’s law in words: What occurs when expanding magnetic lines of force sweep across (cut) a conductor?

Introduction / Context:
Electromagnetic induction explains the fundamental operation of generators, transformers, and many sensors. The qualitative description ”moving/expanding lines of force cut a conductor” is a classic way of stating the condition for inducing an electromotive force (EMF).

Given Data / Assumptions:

• There is relative motion between magnetic flux and a conductor, or the flux changes with time.
• We focus on the immediate electrical effect in the conductor.
• Resistive load or closed path determines whether current subsequently flows.

Concept / Approach:
Faraday’s law states that the induced EMF around a loop equals the negative time rate of change of the magnetic flux linking that loop: e = −dΦ/dt. When expanding lines of force cross a conductor, flux linkage changes, so an EMF (voltage) is induced. Whether current flows depends on circuit closure and impedance; the primary, universal effect is induced voltage.

Step-by-Step Solution:

Verification / Alternative check:
Generators rotate coils in magnetic fields, creating continuous change in Φ and thus a sinusoidal EMF. Transformers induce voltage in a stationary secondary via time-varying flux produced by the primary.

Why Other Options Are Wrong:

• Current increases: Not necessarily; it depends on circuit impedance and whether the circuit is closed.
• Resistance reduced / Power increased: Neither is a direct consequence of changing flux; they depend on materials and loads.

Common Pitfalls:
Equating induced voltage with guaranteed current flow; an open-circuited loop will have voltage but no current.

Final Answer:
Voltage is induced.