A tightly wound 100-turn coil of radius 10 cm carries a current of 7 A. The magnitude of the magnetic field at the centre of the coil is (take the permeability of free space as 4π×10⁻⁷ SI units):

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(3) 4.4 mT. Given: N=100, r=0.10 m, I=7 A. Idea: at the centre of a tightly wound coil the N turns all contribute alike, so B=(μ₀NI)/(2r). Numerator: μ₀NI=4π×10⁻⁷×100×7=8.80×10⁻⁴. Denominator: 2r=0.20 m. B=(8.80×10⁻⁴)/(0.20). B=4.4×10⁻³ T. =4.4 mT.

A tightly wound 100-turn coil of radius 10 cm carries a current of 7 A. The magnitude of the magnetic field at the centre of the coil is (take the permeability of free space as 4π×10⁻⁷ SI units):

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