Inductance of a coil ___________ when we place an iron bar inside it.

Explanation:

Inductance of a Coil

Definition: Inductance is a property of a coil or inductor that determines how effectively it can store energy in the form of a magnetic field when an electric current flows through it. It is denoted by the symbol ‘L’ and measured in henries (H). The inductance of a coil depends on various factors, including the number of turns in the coil, its geometry, and the material inside or surrounding the coil.

Impact of Placing an Iron Bar Inside the Coil:

When an iron bar is placed inside a coil, the inductance of the coil increases. This phenomenon occurs due to the high magnetic permeability of iron. Magnetic permeability is a measure of how easily a material can support the formation of a magnetic field within itself. Iron has a much higher magnetic permeability compared to air or vacuum, which means it can concentrate magnetic field lines more effectively.

Explanation:

The inductance of a coil is given by the formula:

L = μ × N² × A / l

• μ: Magnetic permeability of the core material (iron, air, etc.)
• N: Number of turns in the coil
• A: Cross-sectional area of the coil
• l: Length of the coil

From the above formula, it is evident that the inductance is directly proportional to the magnetic permeability (μ) of the core material inside the coil. When an iron bar is inserted into the coil, the magnetic permeability of the core increases significantly compared to air, resulting in a larger inductance value.

Iron, being ferromagnetic, enhances the magnetic field within the coil. This increased magnetic field leads to a higher inductance because the coil can now store more magnetic energy for the same amount of current flowing through it. This principle is widely utilized in the design of inductors and transformers where iron cores are used to achieve high inductance values.

Practical Applications:

• Transformers: Iron cores are used in transformers to increase inductance and efficiency.
• Electromagnets: Iron cores enhance the magnetic field strength of electromagnets.
• Inductors: Iron cores are used in inductors to store magnetic energy effectively.

Correct Option Analysis:

The correct option is:

Option 2: Increases

When an iron bar is placed inside a coil, the inductance of the coil increases due to the higher magnetic permeability of iron. This allows the coil to store more magnetic energy, making this option the correct answer.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: Reduces to zero

This option is incorrect because placing an iron bar inside a coil does not reduce the inductance to zero. Iron, being a material with high magnetic permeability, increases the inductance rather than reducing it. Reducing inductance to zero would require a material that completely eliminates the magnetic field, which is not the case with iron.

Option 3: Remains unchanged

This option is incorrect because the inductance of a coil changes when an iron bar is placed inside it. The high magnetic permeability of iron enhances the magnetic field, causing the inductance to increase. Therefore, the inductance does not remain unchanged.

Option 4: Decreases

This option is incorrect because placing an iron bar inside a coil does not decrease the inductance. Instead, the inductance increases due to the improved ability of the iron core to concentrate magnetic field lines. Materials with lower magnetic permeability than air would be required to decrease the inductance, but iron does not fit this criterion.

Conclusion:

Understanding the behavior of inductance in the presence of different core materials is essential for designing electrical components like inductors and transformers. When an iron bar is placed inside a coil, the inductance increases due to the high magnetic permeability of iron. This principle is widely utilized in engineering applications to enhance the efficiency and functionality of electromagnetic devices.