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Difficulty: MediumFundamentals of Electromagnetism and Induction

An automotive technician modifies an electromagnetic solenoid by inserting a soft iron core into its center while keeping the applied direct current (DC) and the number of wire turns constant. What effect does inserting the iron core have on the strength of the magnetic field produced by the solenoid?

  1. A
    The magnetic field strength decreases because the iron core absorbs voltage from the coil windings.
  2. The magnetic field strength increases because iron has high permeability and concentrates magnetic flux lines.Answer
  3. C
    The magnetic field collapses because iron blocks magnetic field generation under direct current conditions.
  4. D
    The magnetic field polarity reverses because the core forces electron flow in the opposite direction through the wire.

Answer

The magnetic field strength increases because iron has high permeability and concentrates magnetic flux lines.
Inserting a ferromagnetic core such as soft iron into a coil increases the magnetic field strength because iron has a much higher magnetic permeability than air. This allows the magnetic lines of force (flux) to flow with far less reluctance, greatly concentrating the magnetic field.

Step-by-Step Solution

1
Identify the factors determining magnetic flux density inside a solenoid
The magnetic field strength is directly proportional to the core material's magnetic permeability (μ\mu), the number of turns (NN), and the current (II).
The formula B=μNILB = \mu \frac{N I}{L} defines the magnetic field strength inside a solenoid of length LL.
2
Compare the magnetic properties of soft iron versus air
Soft iron is a ferromagnetic substance with a magnetic permeability hundreds to thousands of times higher than air.
Permeability measures a material's ability to support the formation of a magnetic field within itself.
3
Determine the resulting change in the solenoid's magnetic field
The soft iron core provides a path of low reluctance, channeling and concentrating the magnetic lines of force (flux).
Since the applied current and number of turns remain constant, replacing air with high-permeability iron significantly increases overall magnetic field intensity.

Key Concept

Magnetic permeability and core material effects on solenoid magnetic field strength
Estimated Time:45s
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Topics

Fundamentals of Electromagnetism and Induction

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