Question 20

The magnetic field of earth at the equator is approximately $$4 \times 10^{-5}$$ T. The radius of earth is $$6.4 \times 10^6$$ m. Then the dipole moment of the earth will be nearly of the order of:

The magnetic field ($$B_{\text{eq}}$$) on the equatorial line of a dipole is given by:

$$B_{\text{eq}} = \frac{\mu_0}{4\pi} \frac{M}{R^3}$$

$$M = \frac{B_{\text{eq}} \cdot R^3}{\frac{\mu_0}{4\pi}}$$

$$M = \frac{4 \times 10^{-5} \times (6.4 \times 10^6)^3}{10^{-7}}$$

$$M \approx 1.05 \times 10^{23}\text{ A m}^2$$

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