Calculate the flux density at a distance of 5 cm from a long straight circular conductor carrying a current of 250 A and placed in air.

The magnetizing field strength due to long straight circular conductor is given by

\(H = \;\frac{I}{{2\pi r}}\;AT/m\)

Where, H = Magnetizing force (AT/m)

I = Current flowing in a conductor (A)

r = Distance between current carrying conductor and the point (m)

also B = μ₀ H

Where, B = Magnetic flux density (Wb/m²)

μ₀ = Absolute permeability = 4π × 10^-7 H/m

Calculation:

Given:

r = 5 cm = 5 × 10^-2 m

I = 250 A

\(B = {\mu _0}H = {\mu _0}\frac{I}{{2\pi r}} = 4\pi \times {10^{ - 7}} \times \;\frac{{250}}{{2\pi\times 5 \times {{10}^{ - 2}}}} = {10^{ - 3}}\)

∴ B = 10^-3 Wb/m²

^{Important Points}

 Magnetic flux density of coil is given by ^{\(B = \;\frac{{{\mu _o}NI}}{{2R}}\)}  T

Magnetic flux density of solenoid is given by \(B = \;\frac{{{\mu _0}\;NI}}{l}\)  T

Magnetic flux density of long straight wire \(B = \;\frac{{{\mu _0}I}}{{2\pi r}}\) T