Introduction:
An air gap is a non-magnetic material placed within a magnetic circuit. It interrupts the flow of magnetic flux, causing several effects on the magnetic circuit. One of the significant effects of an air gap is an increase in reluctance.

Explanation:
To understand why an air gap increases the reluctance, it is essential to understand the concept of reluctance and how it affects magnetic circuits.

Reluctance:
Reluctance is the opposition offered by a magnetic circuit to the flow of magnetic flux. It is analogous to resistance in an electric circuit. Reluctance is determined by the physical properties of the magnetic material, such as its length, cross-sectional area, and permeability.

Magnetic Circuit:
A magnetic circuit is a closed path through which magnetic flux can flow. It consists of a magnetic material, such as iron, with a defined cross-sectional area and length. The magnetic flux flows through this material, and the magnetic circuit is completed.

Effect of Air Gap:
When an air gap is introduced in a magnetic circuit, it disrupts the flow of magnetic flux. This interruption causes several effects:

1. Increased Reluctance: The air gap introduces a non-magnetic material, which has a high reluctance compared to the magnetic material. Reluctance is inversely proportional to the cross-sectional area and directly proportional to the length of the magnetic path. As the air gap increases the length of the magnetic path, it results in an increase in reluctance.

2. Reduced Flux Density: Flux density is the amount of magnetic flux per unit area perpendicular to the direction of flux. When an air gap is introduced, it causes a reduction in the flux density. This reduction is due to the increased reluctance, which hinders the flow of magnetic flux.

3. Divided Flux: The air gap causes the magnetic flux to divide between the magnetic material and the air gap. Some portion of the flux flows through the magnetic material, while the remaining portion passes through the air gap. This division of flux reduces the overall magnetic flux in the circuit.

4. Reduced Magneto Motive Force (MMF): The MMF is the driving force that establishes the magnetic field in the circuit. When an air gap is introduced, it increases the reluctance, which in turn reduces the MMF required to establish the desired magnetic field.

Conclusion:
In summary, the introduction of an air gap in a magnetic circuit increases the reluctance, reduces the flux density, divides the flux between the magnetic material and the air gap, and reduces the magneto motive force. This understanding is crucial in designing magnetic circuits and optimizing their performance.