Electrical Engineering All Engineering Career

The unit of relative permeability is dimensionless.

Relative permeability is a dimensionless quantity that represents the ratio of the permeability of a material to the permeability of a vacuum or free space. Since it's a ratio of two similar physical quantities, it does not have any units associated with it.

So, the correct answer is it is dimensionless.

Ebonite is expected to have the highest permeability among the options because brass, copper, and zinc are all non-magnetic metals with very low permeability and do not respond significantly to magnetic fields. Ebonite is also non-magnetic, but relative to the other listed materials, it can exhibit a slightly higher permeability, even though it remains very low when compared to strongly magnetic materials like iron or steel.

Paramagnetic materials have a relative permeability that is just above 1 because they are weakly attracted to magnetic fields and become only slightly magnetized when an external field is applied. Relative permeability compares a material’s permeability to that of free space, so a value just greater than unity means the material can slightly enhance the magnetic field inside it, but only to a very small extent compared to strongly magnetic materials.

Aluminum and platinum are classified as paramagnetic materials because they are weakly attracted to external magnetic fields and do not retain magnetization once the field is removed. Unlike ferromagnetic materials, which become strongly magnetized, or diamagnetic materials, which are weakly repelled, paramagnetic substances have a small positive magnetic susceptibility. This behavior is why materials like aluminum, platinum, and oxygen fall under the paramagnetic category.

One tesla (T) is equal to 1 Wb/m² (one weber per square meter).

Tesla is the SI unit of magnetic flux density, and it measures the strength of a magnetic field. One tesla is equivalent to one weber (Wb) of magnetic flux per square meter (m²).

So, the correct answer is 1 Wb/m².

Magnetic field intensity is a vector quantity because it has both magnitude and direction and is defined at every point in space to show how a magnetic field acts in a particular direction. Unlike relative permeability, which is scalar and only gives a ratio of material response, magnetic field intensity (H) describes the strength and orientation of the magnetic field. Although flux density (B) and magnetic vector potential (A) are also vector quantities, the key correct option here is magnetic field intensity.

Materials with low retentivity (also known as low remanence) are ideal for making temporary magnets because they lose their magnetism almost immediately once the external magnetizing force or electric current is removed.

Antiferromagnetic materials are those in which the magnetic moments (spins) of atoms align in opposite directions with equal strength, so they cancel each other out and the material shows no overall magnetism. This differs from ferromagnetic materials, where spins align in the same direction to produce strong magnetization, and ferrimagnetic materials, where spins are opposite but unequal, leaving a small net magnetism; ferrites are simply materials that can exhibit ferromagnetic or ferrimagnetic behavior depending on their structure.

To find the magnetic potential difference across the air gap, we can use the formula:

\[ \Delta \Phi = \mathbf{H} \times \ell \]

where:
- \( \Delta \Phi \) is the magnetic potential difference,
- \( \mathbf{H} \) is the magnetic field intensity,
- \( \ell \) is the length of the air gap.

Given that the magnetic field intensity (\( \mathbf{H} \)) is 200 A/m and the length of the air gap (\( \ell \)) is 0.02 m (2 cm), we can substitute these values into the formula:

\[ \Delta \Phi = 200 \, \text{A/m} \times 0.02 \, \text{m} = 4 \, \text{AT} \]

So, the magnetic potential difference across the air gap is \( \mathbf{4 \, AT} \). Therefore, the correct answer is 4 AT.

Magnetic field lines form a continuous loop around a magnet: outside the magnet, they move from the north pole to the south pole, while inside the magnet, they return from the south pole back to the north pole. This closed-loop pattern helps explain why magnetic fields don’t start or end at any point but instead flow continuously through and around the magnet.