The question provides a B-H curve, which shows the relationship between the magnetic flux density (B) and the magnetic field strength (H). The nature of this curve helps in identifying the material based on its magnetic properties.

The options given are:

• Glass
• Steel
• Iron
• Air

Explanation:

The B-H curve shown is a straight line passing through the origin. This indicates that there is no hysteresis (lag between H and B), as this would appear as a loop or curvature on the plot.

Materials can be classified based on their magnetic properties as follows:

• Ferromagnetic: Includes materials like iron and steel, which show a large hysteresis loop due to their high magnetic permeability and remanence.
• Paramagnetic: Such as air, which exhibit a small linear increase of B with H, and typically line up more closely with the origin.
• Diamagnetic: Materials like glass, which show very slight and negative susceptibility to magnetic fields.

Given that the curve is a straight line through the origin, it suggests low magnetic permeability and no hysteresis loss. This is characteristic of non-ferromagnetic materials, specifically paramagnetic materials.

Conclusion:

The material corresponding to the straight line B-H curve is air, as air is a paramagnetic material with a simple linear relationship between B and H and no hysteresis.

Thus, the correct answer is:

• Air