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Difficulty: EasyElectromagnetism and Induction

Which of the following occurs when a direct current flows through an insulated wire coiled around a soft-iron core?

  1. The iron core becomes temporarily magnetized and creates an external magnetic fieldAnswer
  2. B
    The iron core stores electrostatic potential energy between the wire turns like a capacitor dielectric
  3. C
    The direct current is automatically converted into an alternating voltage inside the core
  4. D
    The electric current replaces the voltage in the circuit because they represent the same electrical quantity

Answer

The iron core becomes temporarily magnetized and creates an external magnetic field.
When direct current passes through a coil wrapped around a soft-iron core, the magnetic field generated by the current aligns the magnetic domains in the iron. This creates a temporary magnet (an electromagnet) that produces an external magnetic field as long as current flows.

Step-by-Step Solution

1
Identify the physical effect of electric current passing through a coiled conductor
Current moving through the loops produces a concentrated magnetic field along the axis of the coil
All electric currents generate an associated magnetic field according to the principles of electromagnetism
2
Analyze how placing a soft-iron core inside the coil affects this field
The ferromagnetic iron core aligns its magnetic domains with the coil field, greatly strengthening it and acting as a temporary magnet
Soft iron has high magnetic permeability, allowing it to easily magnetize when exposed to a magnetic field and demagnetize when the current stops

Key Concept

Electromagnetism in Coils with Ferromagnetic Cores
Estimated Time:45s
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Topics

Electromagnetism and Induction

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