Permeability is a property of magnetic materials that determines how easily a magnetic flux is set up within the material. It is denoted by the symbol μ and is a measure of the material's ability to concentrate magnetic lines of force. Permeability is an important factor in various magnetic applications, such as transformers, inductors, and magnetic cores.

Understanding Permeability:
To understand the concept of permeability, it is essential to first understand magnetic flux. Magnetic flux is a measure of the total magnetic field passing through a given area. It is represented by the symbol Φ and is measured in Weber (Wb). The magnetic flux is directly proportional to the magnetic field strength and the area it passes through.

Key Points:
- Permeability determines how easily a magnetic flux is set up in a material.
- It is denoted by the symbol μ and is measured in Henry per meter (H/m).
- Permeability can be classified into two types: absolute permeability (μ) and relative permeability (μr).

Absolute Permeability (μ):
Absolute permeability is a fundamental property of a material and is independent of external factors. It is a measure of how easily a material can establish a magnetic field. In other words, it quantifies the material's ability to conduct magnetic flux. Absolute permeability is measured in Henry per meter (H/m).

Relative Permeability (μr):
Relative permeability, also known as magnetic permeability, is the ratio of the absolute permeability of a material to the permeability of free space (μ0). It is a dimensionless quantity that provides a comparison of a material's permeability to that of free space. Relative permeability is often represented by the symbol μr.

Explanation of the Correct Answer:
In the given options (a) how easily the magnetic flux is broken/cleared, (c) how long the magnetic flux takes to form, and (d) how long the magnetic flux takes to clear are all incorrect interpretations of permeability.

The correct answer, option (b) how easily the magnetic flux is set up, accurately describes the property of permeability. It signifies that a higher permeability material allows for the easy establishment of a magnetic flux, while a lower permeability material resists the establishment of a magnetic field. This property is crucial for various magnetic applications, as it determines the efficiency and effectiveness of devices such as transformers and inductors.