B field and H field are two slightly related terms but they are used for two different fields. In this post, we’ll look at the differences between B field vs H field.

**The actual magnetic field within a substance is represented by the magnetic flux density, which is the pattern of magnetic field lines, or flux, per unit cross-sectional area. On the other hand, the H field is magnetic field strength that is caused by an exogenous current and is not inherent in the substance. **

Vector B is used to depict the magnetic flux density. H is the vector that represents the magnetic field strength or magnetic field intensity. The SI unit of measurement is amperes per meter.** **

In** **simple words, one can understand magnetic field strength H, as a magnetic field that is generated due to the flow of current in a wire, while magnetic flux density B can be understood as a total magnetic field containing magnetization M that is created by magnetic properties of a substance in the field.

The magnetizing field H is fairly modest when a current runs in a wire wrapped around a soft-iron cylinder, yet the real mean magnetic field is rather strong.** **

**Magnetic field strength formula**

Magnetic field strength is calculated by the formula given below;** **

H=B/(μ-M)

Here H is magnetic field strength, B is magnetic flux density, μ is magnetic permeability and M is magnetization.

It is expressed in SI units as Amperes per meter.** **

**Magnetic flux density formula**

Magnetic flux density can be calculated by the formula given below; ** **

**B= Hμ**

Here B is magnetic flux density, μ is magnetic permeability and H is magnetic field strength.

It is expressed in Weber per square meter, which is the same as Tesla [T].

**The relation between B, H, and I **

As we know that magnetic strength, symbolized by H, is a number that characterizes magnetic phenomena from the perspective of their magnetic fields. **The magnetic field strength at a particular position can be expressed in terms of H.** The magnetic field and magnetic strength, as well as the permeability of space, is determined by the intensity of magnetization.** **

**So magnetic strength is a term used to describe magnetic phenomena concerning the magnetic field. The magnetic strength ‘H’ is calculated using the equation B=μ**_{0}**H …………………(1) **

Here H shows magnetic field strength and B is a magnetic field. ** **

Magnetic field B can be expressed as** B= μ_{0}(H+M_{Z}) ……………(2)**

**Here M_{Z} **is magnetization.

Mathematically magnetization and magnetic strength are related by this formula given below;

**M _{Z}**= χH …………..(3)

**Here _{χ}H **is magnetic susceptibility.

Magnetic susceptibility for paramagnetic materials is low and positive, while magnetic susceptibility for diamagnetic materials is low and negative. We may express equations 1,2 and 3 as given below;

**B= μ _{0}(1+χH)……………(4)**

That is how** B= μ_{0} μ**

_{r}

**H**

As** μ= μ_{0} μ_{r} **

So,** B= μ H **

Where** μ_{r}=(1+χ)**

** μ_{r}** is a dimensionless quantity and also called relative magnetic permeability of the material.

**If I** is the magnetization intensity and B is the magnetic field within the material, then magnetic strength H in vector form may be represented as below;

** H= (B\ μ_{0}**)

**-I**

Again simplifying,

So the relation between B, H and I **is B=μ _{0}(H+I)**

**Hysteresis loop (B-H Graph) **

The Hysteresis curve is obtained by plotting Magnetization M or Magnetic Field B as a relation of Magnetic Field Strength H (i.e. M-H or B-H graph). A ferromagnetic material’s permeability can be negative or positive and can vary from zero to infinity. ** **

**Hysteresis is described as the delay in a variable attribute of a system concerning the effect that produces it when that effect changes. **In ferromagnetic materials, the magnetic flux density B falls behind the fluctuating exterior magnetizing field strength H. **The hysteresis curve is generated by displaying the graph of B-field versus H by putting the material through a full cycle of H values, as shown below **

Assume a ferromagnetic material sample that has not been magnetized. **At O, the magnetic field strength H is originally zero. When H is raised steadily over time, magnetic induction B rises nonlinearly along the magnetization curve (OACDE).** Nearly all of the magnetic domains are oriented parallel to the magnetic field at point E.** **

A further rise in H does not result in a boost in B. The magnetic saturation point of a substance is designated by E. Permeability values produced from the equation** μ**=

**B\H**along the curve is usually positive and span a large range. At the “knee” (point D) of the curve, the greatest permeability that is

**10**occurs.

^{5}**μ**_{0}**After that H is reduced to zero and B decreases from its saturation point E to that point F. **Some magnetic domains fail to keep alignment but some magnetic domains keep their alignment and. This indicates that the material still has some magnetic flux density B.** **

The curve for decreasing H values (demagnetization curve EF) is displaced by a quantity FO from the curve for rising H values (that is magnetization curve OE). **The quantity of FO shift is referred to as retentivity.**

At point “I,” B achieves saturation in the opposite direction as H increases to high negative values. Almost all magnetic domains are aligned in opposite directions to point E of positive saturation. **H is switched from its most negative to its most positive value. Then B arrives at point “J.” This point demonstrates residual magnetism of the same order as for positive H values (OF=OJ). **

H is grown in a positive way from zero to maximum. Then, at point “K,” B reaches zero. It does not, therefore, travel through the graph’s origin. The quantity of field H necessary to cancel out the residual magnetism OJ maintained in the reverse way is shown by OK.

**H is raised from location k in a positive direction, then B approaches saturation at point “E” and the loop is closed. **

**Frequently asked questions FAQs **

**Q. What is retentivity? **

A measurement of the remaining flux density related to a magnetic material’s saturation.

**Whenever a substance’s magnetization is removed following saturation, it can still preserve a little quantity of magnetic field (The value of B at point E on the hysteresis curve). **

**Q. What is residual magnetism or residual flux?**

The remnant magnetism and retentivity are the identical when the material is magnetized to saturation.

**The** **magnetic flux density B remains in the substance when the magnetizing field strength H is zero. It might be lower than the retentivity value. **

**Q. What is Coercivity? **

**It refers to the amount of reversed magnetizing field strength that must be given to a magnetic substance for the magnetic flux density of ferromagnetic material to revert to zero after saturation. (On the hysteresis curve, the value** **of H at point G.)**

**Q. What is Reluctance?**

**It refers to a ferromagnetic material’s resistance to the formation of a magnetic field. The impedance in an electrical circuit is equivalent to reluctance. **

## **Q. What is Permeability**?

**The flexibility with which a magnetic flux may be created in a material is measured by its permeability. In the B-H graph, X is negative in the II and IV quadrants and positive in the I and III quadrants (i.e. the Hysteresis curve).**