Magnetic Field Strength
Magnetic field strength at any point within a magnetic field is numerically equally to the force experienced by a N-pole of one weber placed at that point. Hence, unit of H is N/Wb. Suppose, it is required to find the field intensity at a point A distant r metres from a pole of m webers. Imagine a similar pole of one weber placed at point A. The force experienced by this pole is
Also, if a pole of m Wb is placed in a uniform field of strength H N/Wb, then force experienced by the pole is = mH newtons.
It should be noted that field strength is a vector quantity having both magnitude and direction
Magnetic Potential
The magnetic potential at any point within a magnetic field is measured by the work done in shifting a N-pole of one weber from infinity to that point against the force of the magnetic field. It is given by
It is a scalar quantity. (Refer article – Potential at a Point)
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Flux per Unit Pole
A unit N-pole is supposed to radiate out a flux of one weber. Its symbol is Φ. Therefore, the flux coming out of a N-pole of m weber is given by
Φ = m Wb
Flux Density
It is given by the flux passing per unit area through a plane at right angles to the flux. It is usually designated by the capital letter B and is measured in weber/meter2. It is a Vector Quantity.
It ΦWb is the total magnetic flux passing normally through an area of A m2, then
B = Φ/A Wb/m2 or tesla (T)
Intensity of Magnetisation
It may be defined as the induced pole strength developed per unit area of the bar. Also, it is the magnetic moment developed per unit volume of the bar.
Let m = pole strength induced in the bar in Wb
A = face or pole area of the bar in m2
Then I = m/A Wb/m2
Hence, it is seen that intensity of magnetisation of a substance may be defined as the flux density produced in it due to its own induced magnetism.
If l is the magnetic length of the bar, then the product (m × l) is known as its magnetic moment M.
Susceptibility (K)
Susceptibility is defined as the ratio of intensity of magnetisation I to the magnetising force H.
∴ K = I/H henry/metre.
Read article – Force Between Two Parallel Conductors
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