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PGCIL DT Electrical 13 Aug 2021 Official Paper (NR I)

Option 3 : working flux density

Magnetic Field Strength(H): the amount of magnetizing force required to create a certain field density in certain magnetic **material per unit length.**

Intensity of Magnetization(I): It is induced pole strength developed per unit area inside the magnetic material.

The net Magnetic Field Density (Bnet) inside the magnetic material is due to:

- Internal factor (I)
- External factor (H)

∴ Bnet ∝ (H + I)

Bnet = μ0(H + I) …. (1)

Where μ0 is absolute permeability.

Note: More external factor(H) cause more internal factor(I).

∴ I ∝ H

I = KH …. (2)

And K is the susceptibility of magnetic material.

From equation (1) and equation (2):

Bnet = μ0(H + KH)

Bnet = μ0H(1 + K) …. (3)

Dividing equation (3) by H on both side

\(\frac{{{B_{net}}}}{H} = \frac{{{μ _0}H\left( {1 + K} \right)}}{H} \)

(1 + K = μ_{r})

B_{net} = μ0μrH

∴ \(H=\frac{B_{net}}{μ_oμ_r}\) A/m

**Hence, Magnetic Field Strength or Ampere per turns per unit length depends on:**

1. Working flux density (B_{net})

2. Nature of magnetic material that is permeability (μ_{r})

3. Internal factor of magnetization or Intensity of Magnetization(I)