The Earth's magnetic field at some place on the magnetic equator of the Earth is 0.5×10⁻⁴ T. Taking the radius of the Earth at that place as 6400 km, the magnetic dipole moment of the Earth is A m². (μ₀=4π×10⁻⁷ T m A⁻¹)

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(2) 1.31×10²³. Given: equatorial field B_E=0.5×10⁻⁴ T at R=6400 km=6.4×10⁶ m. Idea: the Earth behaves as a short magnetic dipole at its centre. A point on the magnetic equator lies on that dipole's equatorial line, where B_E=(μ₀)/(4π)M/(R³). Rearranged: M=(4π)/(μ₀)B_E R³=(B_E R³)/(10⁻⁷), because (μ₀)/(4π)=10⁻⁷ T m A⁻¹. R³=(6.4×10⁶)³=2.62×10²⁰ m³. M=(0.5×10⁻⁴×2.62×10²⁰)/(10⁻⁷)=1.31×10²³ A m².

The Earth's magnetic field at some place on the magnetic equator of the Earth is 0.5×10⁻⁴ T. Taking the radius of the Earth at that place as 6400 km, the magnetic dipole moment of the Earth is _______ A m². (μ₀=4π×10⁻⁷ T m A⁻¹)

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