Question

Find the magnetizing field H and the magnetic flux density point of B at (a) a 105 mm from a long straight wire carrying a current of 15 A and (b) the center a 2000-turn solenoid which is 0.24m long and bears a current of 1.6A

Answer 1

Distance of the point P from long wire = d = 105 mm = 0.105 m
i = 15 Amp

Magnetic Flux density (field) B due to a long straight wire carrying current i

    B = μ i / (2πd)
        = 4 π * 10⁻⁷ * 15 /(2 π 0.105)  T
        = 2.857 * 10⁻⁵ T

    H = Magnetizing field = B /μ = 22.72 Amp/meter

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Solenoid:

Length L = 0.24 m
N = 2000 turns
n = turns/unit length = 2, 000/0.24 = 25, 000/3  per meter 
i = current = 1.6 Amp

Magnetic field B (Flux density) due to a solenoid , inside the solenoid near the axis
     B = μ  n i = μ (N/L) i
     B = 4 π * 10⁻⁷ * 25,000/3 * 1.6 A
        = 1.675 * 10⁻² Tesla

 H = Magnetizing field = B/μ = 40000/3 = 13, 333.3 Amp/meter