A long straight circular conductor placed in air is carrying a current of 250 A. Find the magnetising force at a distance of 5 cm from the conductor.

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

\(H = \frac{I}{{2\pi r}} = \frac{{250}}{{2\pi\times 5 \times {{10}^{ - 2}}}} = \frac{2500}{\pi}\)

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