Question:
If magnetic field at equator is 0.4 G, earth's magnetic dipole moment is of order: (R = 6400 km)
If magnetic field at equator is 0.4 G, earth's magnetic dipole moment is of order: (R = 6400 km)
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Earth behaves like a giant bar magnet in dipole approximation.
Updated On: Jun 17, 2026
- $10^{18}$
- $10^{17}$
- $10^{26}$
- $10^{23}$
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Verified By Collegedunia
The Correct Option is B
Solution and Explanation
Step 1: Convert units: \[ B = 0.4G = 0.4 \times 10^{-4}T = 4\times10^{-5}T \]
Step 2: Magnetic field at equator: \[ B = \frac{\mu_0}{4\pi} \frac{M}{R^3} \]
Step 3: Rearranging: \[ M = \frac{4\pi}{\mu_0} B R^3 \]
Step 4: \[ \frac{4\pi}{\mu_0} = 10^7 \]
Step 5: \[ R = 6.4\times10^6 \Rightarrow R^3 \approx 2.6\times10^{20} \]
Step 6: \[ M = 10^7 \times 4\times10^{-5} \times 2.6\times10^{20} \]
Step 7: \[ M \approx 10^{17} \]
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