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Earth’s magnetic field can be approximated by that of a dipole located at its center. If this dipole has a magnetic moment of about 8 × 10²² A m², then the magnetic field strength near the Earth’s equator (take Earth’s radius as 6.4 × 10⁶ m) is approximately

1. 0.6 Gauss
2. 1.2 Gauss
3. 1.8 Gauss
4. 0.32 Gauss

Correct answer: 0.32 Gauss

Solution

B = 1e-7 * 8e22 / (6.4e6)^3 = 1e-7 * 8e22 / 2.62e20 = 3.05e-5 T = 0.305 Gauss, i.e. about 0.32 Gauss.

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