Question

The Earth's magnetic field approximately ranges between:

• A. 250 and 650 microteslas
• B. 25 and 65 microteslas
• C. 2.5 and 6.5 microteslas
• D. 0.25 and 0.65 microteslas

Hint:

Typical surface magnetic field = 25–65 μT. Poles stronger, equator weaker.

Answer 1

The Correct Option is B

To determine the correct range of Earth's magnetic field strength, we need to examine measurements from geomagnetic observatories and scientific studies.

1. Measurement Units and Scale:
Earth's magnetic field is measured in microteslas (μT), where:

• 1 μT = 10^-6 tesla
• This is equivalent to 1 nanotesla (nT) = 0.001 μT

2. Global Field Strength Measurements:
Scientific observations show:

• At the surface, field strength varies from 25 to 65 μT
• Equatorial regions: ~30-35 μT
• Polar regions: ~60-65 μT
• The field weakens with altitude (~0.3 μT at 1000 km)

3. Why This Range is Correct:
The 25-65 μT range accounts for:

• Latitudinal variations (stronger near poles)
• Local magnetic anomalies
• Temporal variations (daily and secular changes)

4. Ruling Out Other Options:

• 250-650 μT: Too strong (10× actual values)
• 2.5-6.5 μT: Too weak (10× smaller)
• 0.25-0.65 μT: Extremely weak (100× smaller)

5. Practical Examples:
For comparison:

• Typical fridge magnet: ~5000 μT
• MRI scanner: ~1,000,000 μT
• Earth's field is relatively weak but globally significant

Final Answer:
The Earth's magnetic field ranges between $\boxed{\text{25 and 65 microteslas}}$.